摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 892 FIRST REPORT TO THE ATMOSPHERIC APPENDIX TO PART I. A. INFLUENCE OF DIMENSIONS OF TEST-PLATE UPON EXPERIMENTAL RESULTS. (a) Influence ufArea.-It may be observed that evidence has been ob- tained, under both indoor and open-air conditions of exposure, indicating that wetght imrement per unit areu increases slightly as the total area of the specimen decreases. This, of course, is quite intelligible in the light of the visual results which have been recorded in respect to the apparently greater amount of action on or near the edges of the specimen, and it emphasises the necessity of uniformity in the size of test-plate if comparable results are to be obtained. (b) Iiz$uence of Thickness.-In the case of copper, the influence of thick- ness of specimen has also been investigated, with, however, negative results ; i.e.plates of different thickness, but otherwise similar, have given practically identical weight-increments. Moreover, from the form of the weight-incre- ment curves obtained with this metal, it would be expected that the thick- ness of the specimen would be a factor of relatively small importance, even in the case of very prolonged exposure, and, indeed, there does not appear to be any evidence of abnormality in this respect under conditions of actual service. On the other hand, it is a matter of frequent observation that the longer life of iron articles of thick, as compared with those of thin section, is in appreciably greater proportion than the relative thickness of the materials.It is of interest to note that while other causes may also contribute, an explanation of this phenomenon is available in the shape of the weight- increment curve for iron (Fig. z j B), the significance of which, in relation to the function of the corrosion-product, was discussed in Section V.CORROSION RESEARCH COMMITTEE 893 B. OPTICAL RESULTS : EXAMPLE OF EXPERIMENTAL DATA. RESULTS OBTAINED UPON PLATES OF g o / ~ o BRASS, AT 14 DAYS’ EXPOSURE ONLY, IN ATMOSPHERE TYPE 2 (“ TANK-ROOM ”). -- After 14 Days’ Exposure. Mark. Hard or Annealed. Hard 19 Annealed i 1 Hard 1 9 Annealed 9 9 Surface Condition. (‘ Dull ” 9 9 3 9 1 9 Bright” 11 3 9 9 9 How Polished. Works L L A ” By hand Works L L A ” By hand Works (‘ A ” :rant or Back of Plate. Initial Retlec- tivity. Ro. 57 64 70 69 64‘5 63’5 52 49 80‘5 80.5 81 81‘5 85 83’5 78.5 86.0 Actual Xeflec- tivity. R f . 42-8 49’0 52’5 55‘2 48’5 49 ‘2 36.8 40.0 57‘5 62.0 59‘5 64’5 61.0 66.0 59’5 67-2 Per Cent Loss. to- Rt) 100 Ro 25-0 23’5 25.0 20’0 25 22 29 19 28-5 23 24 28 21 2 1 24 22 Mean of falues of 3ack and Front . 124.2 122‘5 +3’5 1 24’0 f.26-0 122-5 } 24’5 } 23 ‘0

ISSN:0014-7672    

DOI:10.1039/TF9241900892

出版商:RSC    

年代:1924

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. CORROSION RESEARCH COMMITTEE 893 PART 11. LABORATORY EXPERIMENTS. Introductory Note.-At the time the work of the present research was commenced, the only available information relating to the mechanism of (atmospheric) oxidation of the non-ferrous metals was that due respectively to Jordis and Rosenhaupt in 1908, and to Berger in 1914. Each of these investigators had conducted experiments of a high order of accuracy with the primary object of determining whether or not the common non- ferrous metals combine with oxygen at the ordinary temperatures.The earlier workers (employing both air and oxygen as the gaseous agent) came to the conclusion that for any action to take place, with or without the pre- sence of water vapour, temperatures higher than atmospheric were necessary. Berger, on the other hand (experimenting with the metal in contact with the gas, and measuring the pressure of the latter), concluded that copper unites with dry oxygen at ordinary temperatures, although the process is not visible to the eye.Berger, however, although he dried his oxygen by the aid of potassium, and strong sulphuric acid, suggested that ‘‘ ultimate traces ” of water might be indispensable to the reaction. This worker also LOC. cit. (vide p. 849).894 FIRST REPORT TO THE ATMOSPHERIC studied the increase in the rate of oxidation with increasing temperature, and made the interesting observation that the very rapid increase observed beyond a certain temperature appeared to be directly related to the con- centration of the film of gas condensed upon the surface of the metal. Although the foregoing results are of great theoretical interest, one very important respect in which the conditions under which they were obtained, differ from those envisaged by the present research, remains to be noted.Thus, in both the investigations which have just been considered, combina- tion of the metal with oxygen was exclusively involved. Under ordinary conditions, however, and more especially, of course, in towns, the air of every-day life contains other chemically reactive constituents besides oxygen, and it is obvious that the (‘ tarnish ” which is ordinarily observed upon a metal surface may not have been produced by union with oxygen at all. Accordingly, in the present work the plan, in the first place, has con- sisted in the employment of air as occurring locally, the characteristic effects of which upon metal surfaces have already been noted in Part I.of this re- port. This has been drawn, either directly or after treatment for the removal of certain constituents, through tubes containing suitably prepared metal specimens. (The size of these specimens has been not more than I inch square so that they have readily lent themselves, where necessary, to ex- amination under the microscope.) Such a method is evidently not so academic as those just indicated, where a definite reaction was made the subject of intensive study. In the present instance, however, where not even the nature of the reactions was definitely known, some exploratory qualitative work was clearly necessary. For this purpose the above (“analytic ’7 method appeared to be more suitable, especially in view of the facility with which such experiments could be conducted concurrently with the “ field tests ” of Part I., and the obvious advantage of employing the same air in the two types of test.Nevertheless the importance of conduct- ing experiments of the purely (‘ synthetic ” type has been kept in view from the outset, and already certain tests have been made upon these lines. A description will now be given of the experimental results obtained, for which purpose it will be convenient to retain the distinction between the type of experiment which has just been indicated. A. EXPERIMENTS EMPLOYING AIR: ENTIRE, OR WITH CERTAIN CONSTITUENTS REMOVED. (I) Influence of Temperature qf MetaZ. - Two polished copper tubes were each fitted inside an ordinary Leibig’s condenser so as to take the place of the inner glass tube.Warm water (average temperature, 25OC.) was circulated through one tube, and cold water (average temperature, 15’ C.) through the other. Air (from outside the building) was in each case drawn through the annular space outside the tube at, as nearly as possible, an equal rate. The experiment was continued for a little over a month, during which time the mean temperature of the cold tube was about 10’ and that of the warm tube about zoo (C.) above the dew-point of the air passing over them. In each case the tarnishing was most severe (nearly black) at the point where the air first impinged upon the metal surface, diminishing rapidly in intensity away from this point, the exit end of the tube being apparently qui:e unaltered.7h generad degree of tarnish was much greater on fhe warm than on the coZd tube. ConcZusions.-(a) Evidently the “ tarnishing constituents ’’ are present in the air in very small proportion, and are of such a character that they areCORROSION RESEARCH COMMITTEE 895 greedily taken up by the first metal surface upon which they impinge. (b) The characteristic tarnishing phenomena upon the surface of the metal are clearly dissociated from any dew-point effect (thus confirming the conclusion reached in Part I., in respect to plates exposed in the ‘‘ base- ment ”) ; indeed they increase in intensity when the temperature is raised still further above the dew-point. I t would be interesting to trace the behaviour of the metal as the temperature is progressivZy increased to higher limits, but this has not yet been done.(2) Efect of Washing th Air through Water.-The arrangement of this experiment resembled that of the one just described, except that the air, instead of passing directly over the metal tubes, was first led through three wash-bottles containing distilled water in order to saturate it with water vapour (average temperature of saturated air = I 7’ C.). This experiment was continued for over five weeks, at the end of which time no alteration whatever was visible on the warm tube, and only a faint trace of tarnish (bluish tinge) on the cold tube. ConcZusi.ns.-(a) The ‘‘ tarnishing constituents ” are evidently very effectively removed by washing through water. (b) Air from which soluble impurities have been removed by washing, but containing water vapour almost to the point of saturation is without visible effect upon copper, even when in constant (slow) motion over the metal for considerable periods.(c) The visible effects produced by oxygen and a thin film of liquid water only are extremely small, indeed quite negligible in comparison with the effects produced by ordinary (polluted) air in the absence of liquid water. (3) E f e c t of Passing Air over Specimens Contained in a Tube.--In subsequent experiments, the specimen has been contained in a glass tube through which air has been drawn. I t is of interest to note that the general effect of drawing air over a row of‘ specimens so contained is that the first specimen receives the brunt of the attack, to the virtual exclusion of those which follow.Not only this, but the effect is very largely con- centrated upon that edge of the first specimen which is nearest the inlet end of the tube. Conchion.-This result evidently confirms that of (I) (above) as to the rapidity with which the tarnishing constituents are removed by the first (suitable) metal surface with which they come into contact. (4) Efect of Fi’dtering t h Air through Cotton- Wool.-Parallel experi- ments have been conducted by placing comparable specimens in glass tubes and drawing air over them at a similar rate (I) directly, ( 2 ) after filtering through an efficient filter of cotton wool. In the case of copper, no difference whatever was discernible up to a period of two months, the air passing through continuously at a slow rate (approximately 4 cubic foot per hour). The air was above the dew-point for the whole time, and the characteristic tarnishing effects were observed in each case.With 60/40 brass, however, the effect of #hered air at the end of a similar period had been directed almost entirely upon the alpha (copper-rich) constituent, whereas in similar experiments with unfiltered air the action had been con- centrated upon the beta constituent. Conclusions.-This latter result is of interest in connection with the “ fogging ” of the high-zinc brasses observed in the “ field tests ” (Section z of Part I.), and points to the fact that the “fogging ” is brought about by solid or liquid particles1 present in the atmosphere as distinct from en- tirely gaseous constituents.On the other hand such particles apparently This would evidently include sulphuric acid.896 FIRST REPORT TO THE ATMOSPHERIC have no effect upon copper under similar conditions ; and the experiment shows that the characteristic tarnishing effects observed upon copper above the dew-point, are brought about entirely by gaseous agents. ( 5 ) Efect of ‘ I Filtering” the Air through Granulated Silver.-Two exactly similar pieces of copper were placed each in a similar glass tube through which air could be drawn at an approximately equal rate. I n each instance the air was filtered through cotton wool before passing over the copper, but in one it was also led through a tube packed with granulated silver. The very striking result then obtained that whereas the usual pro- gression of colours developed upon the specimen over which the untreated air was passed, the other specimen (preceded by the I L silver filter ”) re- mained apparently unaltered for quite a considerable period. At the end of six weeks (when the experiment was dismantled) this specimen showed only the merest trace of discoloration, whilst the other had tarnished very severely, being, in fact, nearly black on the extreme edge.Conclusions. - Clearly the constituents of (polluted) air which bring about the characteristic colour changes on the surface of copper are just those to which the tarnishing of silver is due, the behaviour of the two metals, above the dew-point, apparently being regulated by similar causes. (It should, however, be noted that simultaneous exposure of the two metals to the same atmosphere, above the dew-point, shows that the characteristic colours develop much more quickly upon copper than upon silver.) From the known properties of silver, it is therefore evident that the visible tarnish- ing of copper under such conditions is due, not to combination with oxygen, but to reaction with sulphur compounds.( 6 ) Efect of Removal (and Additiun) of Water Yapour.-(a) Two similar pieces of copper were arranged, as before, for the drawing of air over them at approximately equal rates. In one case only a glass-wool filter preceded the copper, whilst in the other a train of drying tubes was included, consisting of several calcium chloride bulbs, and finally two tubes containing phosphorus pentoxide. On the sixth day the copper over which the normal air had passed was very appreciably tarnished, whilst that exposed to the dry air was still perfectly bright, the volume of air which had then passed over the two specimens being 49 and 5 1 cubic feet respectively.The experiment was continued for several more days until approximately 7 0 cubic feet of air had been drawn through each tube, at which time the copper in the ‘ I dry ” tube was still perfectly free from any sign of tarnish. ConcZusions.-This experiment, per se, would appear to leave no room for doubt that the presence of water vapour is definitely necessary for tarnishing to occur. Nevertheless, considering the available evidence as a whole, it was felt expedient to carry out the following additional experi- ments. (b) The arrangement here was similar to that of the previous experiment, with the addition of the following piece of apparatus between the drying train and the tube carrying the specimen ; a glass wash-bottle with stoppered funnel so that water could be admitted without the admission of air, except such as had passed over the drying materials.The experiment was carried out as before, except that from time to time a small quantity of distilled water was run into the bottle, each portion being allowed to evaporate com- pletely before a fresh addition was made. The somewhat striking result then obtained that whereas tarnishing of the blank ” proceeded in the usual manner, apparently no change was produced upon the specimen over which the treated air was passing.At the end of nine days, when 64 cubicCORROSION RESEARCH COMMITTEE 897 feet of air had passed through each tube, the one specimen displayed the usual progression of colours (from steely gray to deep orange), whilst the other showed no change beyond a mere dulling of the surface. (The total quantity of water evaporated was approximately 2 0 c.c.) Cu?tE/usions.-If the inhibition of tarnishing in (a) had been genuinely due to the removal of water vapour, it was somewhat difficult to see why the uddift'on of water vapour to the desiccated air should not have restored its capacity for tarnishing. There appeared to be only two directions in which the explanation could lie; either (I) the drying materials having actually removed whatever was responsible for tarnishing, or ( 2 ) the artificial addition of water vapour having itself in some way inhibited the process.No direct evidence relating to the former alternative has yet been obtained ; with regard to the latter, however, the following experiment was carried out. (c) Two similar copper specimens were again arranged '' in parallel," over each of which room air was drawn at the same rate. In one case only a small filter of cotton wool preceded the copper whilst in the other, a wash-bottle similar to that described above was interposed between the filter and the specimen. Water was again admitted in small quantities to the wash-bottle, whilst air was passing through. (The rate of evapora- tion was naturally considerably slower than obtained in the previous instance ; as before, however, each small edition was allowed to evaporate completely before a fresh portion was admitted.) The action apparently proceeded in a similar manner to that observed in the previous experiment, a considerable degree of tarnish having been reached upon the " blank " specimen before any appreciable change had been produced upon the other.At the end of nine days (when the blank had reached a similarly ad- vanced stage of tarnish to that described above) the specimen over which the " humidified " air had passed was seen to be in a verly early stage of colour change, this being practically confined to a narrow orange band at the extreme edge. ConcZusions.-The presence of excess of water vapour considerably reduces the rate of tarnishing of copper (in so far as this is produced by exposure to the atmosphere employed in the experiment 2).This result, surprising though it appears according to prevailing views, certainly agrees with results which have been obtained in connection with Part I. of the present report. Reverting to Experiment (6) it will now be apparent that the action of water vapour is itself quite sufficient to account for the result observed. Nevertheless, it should be pointed out that this does not necessarily ex- clude the possibility of the tarnishing constituents being removed in some way by passage over the drying agents. The results of Experiment (c) would indeed appear to throw very considerable doubt upon the necessity for the presence of water vapour, so that, in spite of the apparent con- clusiveness of Experiment (a) the question cannot be regarded as having been definitely settled.(7) Influence of" Period."-In view of the results of Part I., relating to the constancy of the form of the '' surrosion curve " for copper in an un- saturated atmosphere, it is rather remarkable that the initial rate of tarnish- ing, as judged by the eye, varies very much according to the period during which the metal is first exposed. The following figures will illustrate this point. On Friday, 6th April, an experiment was started, air being drawn The delivery tube, however, reaching only one-third of the way down the bottle. I.e. that of the '' basement." (Vi& Part I. of report.)898 FIRST REPORT TO THE ATMOSPHERIC (from outside the building) over an emeried copper specimen.On Tuesday, 10th April, this specimen was distinctly tarnished, and the total volume of air which had passed over was 15 cubic feet. I t so happened that this period coincided with a particularly cold spell of weather, the neighbouring Meteorological Office records indicating a mean temperature for the period of 43.6” F. The weather then changing quite suddenly, the specimen was repolished and replaced. For the next three days a com- paratively warm spell prevailed (the mean temperature being 56” F.) and on the Friday, when 2 2 cubic feet of air had passed over the specimen, there was no sirn of tcrmish. ConcZusions.--The above figures are given because they happen to be the only ones available which give numerical expression to a state of affairs about which no doubt is felt from the results of general observation, i.e.that a greater rate of tarnishing is associated with colder weather, the cause presumably being that more coal is then burnt, with consequent greater pollution of the atmosphere. B. EXPERIMENTS EMPLOYING CERTAIN GASES AND VAPOURS : ALONE, OR ADMIXED WITH AIR. The most obvious sulphur compound which could be held responsible for the characteristic tarnishing effects is, of course, hydrogen sulphide, and indeed such effects are frequently assumed to be caused by this compound. Whilst there can be no question of the activity of hydrogen sulphide in this respect in so far as it is actually present in the atmosphere, instances of very rapid tarnishing (as described in Part I.) have been observed under conditions where the concentration of the gas has been negligibly minute, indicating that other causes must be sought.The only other obvious constituent of polluted air which might function in this manner is, clearly, sulphur dioxide (this being the gaseous sulphur compound present in by far the largest proportion), although it is not obvious how it could, and experiment showed, indeed, that it does not bring about the familiar changes. What actually happened was that a “creamy” film was first produced upon the copper surface which subsequently passed into a permanent reddish-brown appearance. The suggestion then arose as to whether there might be among the products of combustion of coal some compound which, in conjunction with su&hur dioxide, might give rise to the characteristic tarnishing effects, and a first experiment was accordingly conducted with benzene, this being a substance known to be present in very small quantities in air polluted with such products of combustion.Two copper specimens were arranged in parallel tubes, sulphur dioxide being passed over one, and sulphur dioxide admixed with benzene vapour over the other, the rate of flow being maintained as equally as possible in the two instances. It is significant that whereas in the course of a day the sulphur dioxide alone had only given rise to the reddish-brown appear- ance already noted, the mixture had produced upon the other copper specimen a very dark-brown appearance, approaching black at the edge on which it had first impinged. The experiments had reached this stage when, very recently, a paper was published by U.R. Evans 1 describing a number of qualitative experi- 6 L The Mechanism of the So-called ‘ Dry Corrosion ’ of Metals,” Trans. Favaday SOC., 19 (1923), 201.CORROSION RESEARCH COMMITTEE 899 ments of the type now described as “ synthetic,” curiously anticipating a number of the tests with which it was proposed to proceed in the course of the present research. One of these experiments, in particular, has a very important bearing upon the present work, and is therefore quoted. Two strips of copper were suspended respectively in stoppered test- tubes, the first containing a small quantity of sulphuric acid and the second a small quantity of water, the specimen being suspended in the upper part of the vessel in each case.After leaving overnight, a slow stream of hydrogen sulphide was passed into each vessel. “ The specimen over water had become first a fine rose, then purple, then steely grey, before the specimen placed over sulphuric acid showed any change at all. After an hour, the specimen over water was dark grey, whilst the specimen held over sulphuric acid had arrived at the stage reached by the specimen over water in about a minute.” Evans concluded from this, and similar results, that the film of liquid, which he assumes to be present (adsorbed) upon the metal surface even for extremely low concentrations of water vapour, acts, together with the gas which dissolves in it, as an electrolyte, and that the tarnishing of the metal is brought about by electrochemical action between anodic and cathodic areas in the metal surface.With this view the present author has already had the opportunity of expressing his disagree- ment.l He has recently, moreover, carried out a modification of Evan’s experiment described above, the results of which appear to be of general interest. Three similar strips of copper were suspended in siniilar stoppered ‘‘ wash-bottles,” as follows : (I) over phosphorus pentoxide ; ( 2 ) over phosphorus pentoxide, the bottle containing in addition a small glass vessel placed underneath the delivery tube; (3) over a small quantity of water. In each case the delivery tube passed only two-thirds of the way down the bottle, and in ( I ) and ( 2 ) the two tubes leading into the bottle were closed with guard tubes filled with calcium chloride.After standing for a day, a little pure benzene (dried over sodium) was introduced through the delivery tube into the small vessel in ( 2 ) , the guard tube being quickly replaced. The whole were then allowed to stand for a further day. A slow stream of hydrogen sulphide was then passed into each vessel for the space of two minutes. During the passage of the gas no change at all was visible upon the specimen over phosphorus pentoxide, whilst characteristic colour changes made their appearance upon the specimen over the dry benzene. The specimen over water behaved in a very striking manner ; for an appreciable time (approximately thirty seconds) no change was visible ; the colour changes then commenced quite suddenly and proceeded with extreme rapidity ; within two minutes after discontinuing the passage of gas it had passed through a deep blue stage and had assumed a steely appearance.At three minutes, on the other hand, the “ dry ” specimen was still practically unaltered, whilst that over the benzene displayed almost the whole series of colour changes previously noted, e.g., “ steely ”-purple-deep orange-light orange. Apart from the fact that the “dry” specimen lagged very considerably behind the specimen over benzene in the development of tarnish, a true comparison of their behaviour was rendered difficult by the circumstance that the sequence of colours did not exactly correspond in the two instances. Thus, after three hours exposure, the appearance of the “dry ” specimen, whilst much the same as that shown within two minutes by the specimen Trans.Faraday Soc., 19 (rgq), 215.goo FIRST REPORT TO CORROSION RESEARCH COMMITTEE over water, could not be exactly correlated with the appearance exhibited at any stage by the specimen over benzene. On the other hand, it is worthy of note that the behaviour of the latter presented a much closer resemblance to the behaviour of the large plates in the field test (Atmos- phere Type I ) than did that of either of the other specimens. Further- more, whilst the observation of Evans as to the accelerating influence of water vapour is amply confirmed by the results of these experiments, the fact that benzene, a typical non-electrolyte, is capable of functioning in a similar manner appears to be fatal to the electrolytic explanation quoted above.With regard to the influence of water vapour it will be observed that the results of these experiments with hydrogen sulphide lead to a conclusion exactly the reverse of that previously reached in the experiments with air, where the rate of tarnishing was considerably reduced by the addition of water vapour. Clearly, therefore, the action of hydrogen sulphide does not provide an analogue of the tarnishing effects actually observed in the atmospheres under investigation. I t is evident, moreover, that much more work remains to be done in the field represented by the present experiments.’ ACKNOWLEDGMENTS. The author wishes to express his great appreciation of the advice and encouragement accorded to him by Professor H. C. H. Carpenter, F.R.S., under whose supervision the research has been conducted, and by whom many facilities have been granted. In the cordial co-operation of the staff of the Metallurgical Department of the Royal School of Mines, he has had an asset whose value he grate- fully acknowledges; he is indebted, moreover, to the staffs of the Applied Optics and Physics Departments of the Royal College of Science for their courtesy in providing facilities for carrying out the optical tests recorded in the Report. The author desires gratefully to record how very much the research owes to the sustained interest and valuable suggestions of Dr. R. S. Hutton, Director of the British Non-Ferrous Metals Research Association. With regard to the supply of materials, the research is particularly in- debted, both to the personal interest of the gentlemen indicated below, and to the generosity of the respective firms, uiz. : Mr. Thos. Bolton (Messrs. Thos. Bolton & Sons, Ltd.) ; Mr. A. Spittle (Messrs. Allen Everitt & Sons, Ltd.); Mr. H. Lancaster (Messrs. Locke, Lancaster, & W. W. & R. Johnson & Sons, Ltd.). Thanks are also due to Mr. J. C. Williams (Messrs. John Haddon & Co.), for help received in connection with the preparation of test-plates. Finally, the author gladly places on record the valuable part taken in the experimental work by Mr. L. Whitby, Research Assistant. ’A resume of the conclusions reached from these experiments will be found in the general summary of the report under the heading of ( I Copper . . . Mechanism of Tarnishing ” (p. 3).

ISSN:0014-7672    

DOI:10.1039/TF9241900893

出版商:RSC    

年代:1924

数据来源: RSC

摘要:

DISCUSSION. Mr. Alan E. Munby, Chairman of the Atmospheric Corrosion Com- mittee of the British Non-Ferrous Metals Research Association: I do not rise to open this discussion because that is a technical matter and not within my province. My real object is the modest one of giving you a short historical account of how this work came to be carried out. The Royal Institute of British Architects some ten years ago was greatly interested, through its Science Standing Committee, in the question of the corrosion and tarnishing of the metals used in building. We have to specify in our work a great many metals, such as different kinds of brass and zinc, which decay with some rapidity, and we were anxious to get some information as to how to reduce the labour necessitated in cleaning these metals, and also how to increase their life.Mr. Crompton first suggested the matter as Chairman of the Science Standing Committee. Some spade work was done and eventually we got into touch with the Department of Scientific and Industrial Research who encouraged us to go forward with the idea. It took some time, and later we were introduced to the Institute of Metals, and Mr. Shaw Scott, the Secretary, did a great deal of valuable work for us, getting all sorts of information and gathering funds from different sources, which latter were necessary before we could get the Department of Scientific and Industrial Research to make an actual financial move. However, we got together sufficient funds in order to launch a scheme and we were about to launch it when a bombshell fell into our midst in the form of a svggestion-or rather something more than a suggestion-from the Research Department, that a larger Committee was being formed to consider corrosion.We got into touch with this Committee, and thanks to the Chairman, Mr. Bolton, we had a very favourable reception and we now form part of that main Committee and we are very well treated by them. They leave us very much to ourselves and allow us to follow our own ideas, but we report to them and through them to the Department of Scientific and Industrial Research. That brings the matter up to date except to say that we are very fortunate in possessing the services of Mr. Vernon and also of Professor Carpenter. We have a difficult problem. The lines on which such a research should go forward are, I suppose, debatable, and I take it that they always will be because there are so many people interested in corrosion from different standpoints. There are many fundamental things to be examined, and it can only be hoped that as the result of the work that has been done already and of the discussion to-night, there will be some tangible outcome.Personally, I know sufficient of science to appreciate the fundamental aspect and I think we should endeavour to get fundamental knowledge as far as possible. The practical issue and fundamental know- ledge, of course, go side by side and it is sincerely to be hoped that as the result of the discussion to-night, the practical work and the acquisition of fundamental knowledge will be carried on together.901902 ATMOSPHERIC CORROSION Professor H. C. H. Carpenter: I should like to begin by saying that I have been in touch with Mr. Vernon’s work from the beginning and to bear my testimony to the great care that he has exercised in planning and carrying out his experiments. As he points out, the greater part of his work was carried out on what he calls field tests, but there is a section of the Report dealing with laboratory experiments. I was very glad to hear Mr. Munby say that fundamental research is necessary in this problem because although I fully agree that the data obtained from the field tests are of great value, I think the six or seven pages at the end of the Report constitute its most valuable section. In saying that I have in mind what has been our experience on another Committee dealing with corrosion.We set out to attack a specific problem in a practical way and we are still at it after ten years and we have found, as we have gone along, that we require to broaden the investigation more and more. I. think all of US who have had experience of it, realise that we should have been wiser to have started on a broader basis, and there- fore I hope that those who are interested in this investigation will be willing to assist in attacking this problem in a fundamental way, because I think that if Mr. Vernon, or anybody who investigates this problem, can tell us what tarnishing and filming and fogging are-and they represent the early stages of corrosion-then they will have solved the problem. I would just like to deal with a few points which seem to me to be of significance in reference to the facts given in the paper.First of all, with regard to the three types of curve, the two parabolas and the straight line. The first parabola has an axis coinciding with the time axis. That is the case of copper where, according to the author, the scale forms a continuous envelope. I should like to ask the author what exactly is his evidence when he says that it is a continuous envelope. In what way has he examined the envelope? Can he tell us anything about its physical character and its thickness? I think this is of the very greatest importance because it appears in this case that the film does constitute a protective surface on the metal and undoubtedly, from the point of view of the problem being attacked, this is the most favourable case of all.Then there is the straight line curve, in which case he says the film is completely permeable. No. 3 case is where the scale is discontinuous and No. I where it is continuous. Is the straight line curve an intermediate case? Does it differ from No. I and if so, in what respect if it is continuous? If it is discontinuous, in what respect does it differ from No. 3 ? Any information on this point will be of the utmost value because it will enable us, I think, to form an opinion as to what it is that happens in the early stages of corrosion. Then, coming to the influence of surface conditions, I think we should note Mr. Vernon’s view that they are “ comparatively unimportant ”. I t appears that he has not observed any striking differences, and that view may comfort those who are attacking this problem from the practical side.Passing on to tarnishing, I gather that Mr. Vernon’s view is that tarnishing is definitely produced by gaseous reagents above the dew point and that water has, on the whole, an inhibiting effect. He is, of course, quite right in saying that sulphur compounds-those produced by the combustion of coal and other carbonaceous materials-are the most important but as far as I can gather, he has only considered hydrogen sulphide and sulphur dioxide. I should like to ask him if he has taken into account organic compounds of sulphur which are undoubtedly produced by the combustion of coal and although present in smaller quantities, may be He does not say whether that scale is also continuous.DISCUSSION 903 very deleterious from the point of view of corrosion. Further information on that point would therefore be useful.I take it that Mr. Vernon’s point is that tarnishing is essentially due to the effects of vapour. In addition, there appear to be two phenomena which are not the same but are closely allied. There is the smoky film liable to be produced on the high zinc- brasses, and the fogging of nickel, and both of these actions appear to be connected with the presence of liquids. In the early stages of the filming of 60/40 brass, the alpha constituent is the first to be attacked, but later on the beta constituent is preferentially attacked. Here the author suggests that probably SO, is producing the attack.That is therefore quite a different phenomenon from “tarnishing” and it also appears to be different from the filming or fogging of nickel. 1 am not quite clear on this, but I should like to ask the author whether the latter is produced by a certain impurity. The fogging of nickel is a temporary condition, up to a certain point, but after a time according to the author it is a permanent effect and therefore the surface of the metal must be altered. I do not think Mr. Vernon has given us any information on the point in the report, but if he can tell us sorriething about it I think it would add to its value. Alternatively, if he has not investigated that, I think that the further investigation of the smoky film in the zinc brasses and the fogging of nickel and its alloys will produce results of great importance to the theory of the subject.I frankly lay greater stress upon laboratory experiments in the early stages of an investigation of this kind because it is possible there to isolate and carry out the experiments under strictly defined and simple conditions. These can be gradually rendered more complex and in that way a definite factor can be picked out which produces a particular result. On the other hand, field tests, valuable though they are, are not under the same control and it is largely a matter of guessing as to what factor produces a particular result. Therefore, while I fully agree that field tests should go hand in hand with laboratory tests I hope that Mr. Vernon will be allowed to devote more time in his work to the laboratory tests, at any rate for a time. I think field tests have had their innings in this paper and as far as I have anything to do with the work, laboratory tests will have a better innings in the next one.Professor C. H. Desch (communicated) : The principal result of the interesting series of observations recorded in the paper is the recognition of three ways in which superficiai corrosion of metals may occur, as shown by the three types of curve connecting change of weight with time. Naturally all transitions between these types may be expected to be possible. The actual resistance of a metal to atmospheric corrosion must depend mainly on whether the tarnish film or rust which is formed is continuous, in which case further action proceeds more slowly, or discontinuous, when action is accelerated.I t is a matter of great scientific interest to determine the reasons for these differences. They are not to be attributed merely to differences of density among the corrosion products, the peculiarly dis- continuous character of iron rust being quite inconsistent with such a simple explanation. The same metal may form either type of corrosion product according to the physical conditions, as when aluminium, which normally forms an adherent and protective film, in the tropics forms a porous coating. The action must be electrochemical and a detailed study by means of the microscope wilI probably throw much light on its mechanism. Mr. U. R. Evans has called attention to the necessity of firmly adherent films, mainly of water vapour, on the surface of metals which are in process Now, what is the alteration?904 ATMOSPHERIC CORROSION of tarnishing, and this factor seems to have great importance.Much re- search work has been done recently, and is now in progress, as to these condensed gas films, which are extraordinarily persistent, even at high temperatures. I t remains to be proved that a dry gas would act on a dry metal, once the surface films have been removed. There is good reason to suppose that there would be no action. The experiment is a difficult one to make; the work of Professor Baker has shown the difficulty of obtaining any substance in a really dry condition. The author’s benzene was not dried under such special conditions, and certainly would not prevent the presence of a film of water which would provide the necessary electrolytic solution.Continuation of the experiments should lead to further interesting results. I t is to be hoped that the ugly word “ surrosion ” will not come into general use. I t does not appear that there is any peculiarity in the process which cannot be described by using such familiar English words as “ rust ” and (‘ tarnish,” and it is undesirable to multiply new coinages. Dr. G . D. Bengough: The paper bristles with a large number of points which one would like to discuss with Mr. Vernon and on which one would like further information. I will, however, only raise one or two that seem of special interest. Can the author give us any information as to any correlation between the impurities present in the metal and the amount of corrosion? H e has used, I understand, zinc of several grades of purity.Has he found that the impurities have had any noticeable influence on the rate of corrosion, or is the latter independent of them? One would rather expect that in the case of zinc, where we are said to have a discontinuous scale, that the impurities would have a noticeable effect on the rate of corrosion if that corrosion is strictly electrochemical in origin. On the other hand, it is possible that in the case of copper the impurities might not have a very great effect on corrosion because apparently there is a continuous scale over the whole surface, which might be supposed to blanket down, to some extent, any action of that kind.The view that the scale on zinc is porous and non-protective is, I think, a new and remark- able one, which I certainly should not have predicted. I imagined- although I know nothing about atmospheric corrosion-that zinc had on it a fairly protective scale and I always thought that galvanising steel had the effect of slowing down the rate of corrosion because of its presence. I t would appear from Mr. Vernon’s work, however, that that is not the case at all. Apparently, the reason why zinc damps down the corrosion is because its oxide coat is neutral, whereas in the case of iron the scale formed is an actual accelerator of corrosion. That appears to be suggested as the real reason why zinc acts so excellently as a protective coating. It is quite clear, I think, that you cannot explain the protective value of zinc as a purely electrochemical action between the two metals, because if you consider an area of iron which has been locally stripped of zinc, that area of the iron will corrode faster than the zinc areas, except those close to the metallic junction.The specific effect of carbon dioxide on zinc, observed by Mr. Vernon, is very interesting because we get a very similar effect in wet corrosion. If you eliminate carbon dioxide from your corroding medium in wet corrosion, you can get an extremely slow rate of corrosion of zinc even in such an active corroding medium as sea-water. If you put zinc into sea-water, first eliminating carbon dioxide, you get a uniform layer of zinc hydroxide on it which increases at a very slow rate for long periods of time. If you admit C02, the hydroxide breaks down locally and you get local pitting.DISCUSSION 905 I should like to ask Mr.Vernon if he can give us any more information about the uniformity of the scales on zinc and copper. That is really only putting a somewhat similar question to that put by Professor Carpenter. Has he seen any signs of local breakdown of the scale, particularly on copper? If you try to carry out experiments in distilled water with copper, and if you carefully polish the copper and get it very smooth and uniform, you can form a tarnish on the copper which seems, in the early stages of corrosion, extremely uniform. In this period you get no pitting, but in the course of time there is some chemical or physical change which has the effect of altering and finally breaking the scale, and then you get pitting occurring at that spot. Has the author noticed anything similar to that in atmospheric corrosion? I t is the local breaking down of the scale which seems to determine the locality of the pitting in copper in conductivity or distilled water.There is one more point; as far as I can gather, the whole of the author’s experiments are Concerned with the tarnishes that form on the thin surface layer that exists on his metals which have all, I think, been polished or (‘worked ” in some way or another. In carrying out wet corrosion experiments, we find a great difference between the behaviour of the actual surface layer-the “ worked ” surface layer-and the underlying material.If the analogy holds for atmospheric corrosion, Mr. Vernon will find sooner or later a great increase in the rate of corrosion. To take an extreme case: suppose we leave a specimen of drawn brass tube in sea- water (stagnant) for a considerable time, and then observe the surface with a microscope-5 o or 60 diameters ; under certain conditions the surface will appear to be unchanged. You can see every minute detail of the drawn surface of the tube and every scratch on the original surface. You might be tempted to say that it is a very good tube because it does not seem to have corroded. But if you touch the surface with a glass point, you are very much disillusioned. This surface layer is shown to be lying on quite heavily corroded metal underneath, and if, instead of carrying out the experiments in stagnant sea-water, you use rapidly moving water you see at once the heavily attacked metal beneath the surface layer.This surface layer, as far as wet corrosion is concerned and leaving out of the question mechanical effects, is very much more resistant than the underlying material. I t is a striking fact which is, I think, explainable, although it requires a great deal of going into. The “worked ” surface layer appears to be structureless, whereas the metal underneath is crystalline ; sooner or later Mr. Vernon will possibly get something of the kind described as he is using “ worked ” metal. He is more likely to get something of that kind in his field experiments and in the kitchen, and especially where he exposes the specimens to rain water.Mr. LJ. R. Evans : I should like to congratulate Mr. Vernon on the monumental work embodied in this report, which has features of very great practical importance and theoretical interest ; over a large part of the subject, I am in general agreement with him, but intend to refer mainly to a few points on which we do not hold the same views. Mr. Vernon has done certain experiments on the action of hydrogen sulphide on copper and he claims to have shown that the presence of benzene vapour is capable of stimulating the tarnishing action of dry hydrogen sulphide on copper. Like Professor Desch, I have a certain amount of doubt as to whether the benzene was quite as dry as it should be, and I would refer particularly to the work of Groschuffl on the question of the drying of organic liquids.E. Groschuff, Zeit. Elektrochem., 17 (I~II), 348.906 ATMOSPHERIC CORROSION Even if we assume that the experiment was carried out with the benzene as dry as can be obtained with sodium, there still seems to be a little doubt as to the conclusion which should be drawn from it. Air dried over phos- phorus pentoxide is not, of course, entirely dry : there is already a small pressure of aqueous vapour, and the question arises as to whether, by introducing benzene dried over sodium, one increases or decreases the pressure of aqueous vapour. Even supposing the tension is not increased, the matter is not conclusive. Mr. Vernon states that the demonstration that inert substances increase the rate of tarnishing, would be '' fatal " to the electrochemical view.If Mr. Vernon will refer to the paper1 which I presented at Manchester, and which he was good enough to criticise, he will find a very large number of examples of the stimulation of corrosion by contact with inert substances. To give merely a single example, let us consider the corrosion of lenticular-shaped pieces of lead at the bottom of a porcelain dish immersed in potassium chloride solution. Along the line where the lead comes close to the porcelain there is a deeply pitted ring; over the rest of the specimen there is only a general tarnishing. The explanation is that the part which is inaccessible to oxygen becomes anodic, and the parts to which oxygen has access become cathodic. At the anodic parts, there is very deep pitting ; at the cathodic parts alkali is produced ; where the lead salt and the alkali meet a rim of lead hydroxide appears.I pointed out in that paper that the electrochemical view alone seems to be capable of explaining these numerous cases of specially marked corrosion at places to which oxygen has not access, and asked the upholders of rival views to suggest alternative explanations. Only one other explana- tion, based on differential adsorption, was forthcoming and I understand that the gentleman who put it forward has subsequently withdrawn it. I take it, therefore, that the electrochemical theory holds the field in explaining the action of inert substances in stimulating corrosion at certain points. I am not saying that benzene has the same action in Mr.Vernon's experi- ment. I am rather inclined to agree with Professor Desch in attributing the phenomenon to the introduction of extra water. Of all the very interesting points brought out by Mr. Vernon, I think there is none more interesting than the fact that he has shown that in many cases the curve connecting weight-increment and time is a parabola, and that the equation governing tarnishing is the same. equation as was arrived at by Pilling and Bedworth for metals oxidising in dry air at high temperatures. That, after all, is what would be expected if the controlling factor is the increasingly slow diffusion of the reactants through the corro- sion product. I am glad to see that Mr. Vernon has omitted to draw the conclusion that the mechanism in Zow-temperature tarnishing in damp atmospheres is the same as h&h-temperature oxidation in a dry atmosphere. One of the interesting features of Pilling and Bedworth's work was that they showed definitely that the oxidation of copper at high temperatures goes on at a rate which is independent of the presence of moisture.I t has been shown by various workers that the rate of direct chemical oxidation becomes very much smaller as we reduce the temperature. I t is well known that at about 220" C. you can produce the first (yellow) interference colour on iron within a minute, whilst the purple arrives within an hour. If you reduce the temperature to about I 70' C. you require several hours to produce the purple interference colour. Tammann 2 has calculated the U .R.Evans, 3'. Inst. Met., 30 ( r g q ) , 239. * G. Tammann, Rec. TYUV. Chim., 42 (~gq), 547.DISCUSSION 907 time which would be needed for the production of the first interference colour at ordinary temperatures in the case of iron exposed to dry oxygen, and he has come to the conclusion that it is 2 5 x 1017 years. He has also calculated similar numbers in the case of other metals. In the case of lead it is shortest (90 years) whilst nickel would require, according to Tammann, 475 x 1017 years. I think, therefore, we may disregard direct chemical oxidation by dry air for ordinary purposes; at any rate this form of attack will not interest the architects very much. The fact that tarnish- ing in a moist atmosphere goes on considerably faster shows that here a very different mechanism is at work.I n a previous communication1 Mr. Vernon suggested that the water might act as a catalyst ; but this would be quite inconsistent with Pilling and Bedworth’s view which Mr. Vernon also seems to accept, that the falling off in the rate of tarnishing is due to the increase in thickness of the obstructive film. If the controlling factor is the rate of diffusion through the film, the velocity cannot be increased by the action of a catalyst; you do not, for instance, increase the rate of diffusion of water through a porous partition by covering it with platinum black. I think, therefore, we have to look for some other cause of the influence of water vapour, and if we can find the cause without introducing any new assumption it will be highly satisfactory.I t is known that metals exposed to air that is not absolutely dry become covered with a sensible film of moisture. Mr. Vernon rather hints in his paper that I have “invented” this film for my own evil purposes. But he himself tacitly admits its existence every time he uses a dessicator in which to allow his platinum vessels to cool. Now we know that when a metal is de@Zy immersedin a liquid, electric currents flow (or at any rate start to flow), between different parts of the metal; if they continue to flow they give rise to corrosion. If the metal is merely covered with a very thin film of moisture, you may expect to find something of the same sort going on, but the controlling factor will normally be different. In the case of a deeply immersed metal, the controlling factor is generally the rate of diffusion of oxygen to the metallic surface.If, however, we start with a clean metal and only a very thin film of moisture on it, there will generally be plenty of oxygen there and the controlling factor may be the very small conductivity of the very thin film. We would expect, therefore, to find that the cor- rosion will be very small if the film consists of pure water, but will be increased if certain substances are present in the atmosphere which can dissolve in the liquid and increase its conductivity. I t is significant, there- fore, to find that certain types of atmospheric pollution do increase corrosion very much. Hydrogen chloride, ammonium chloride, sulphur dioxide, ammonium sulphate and sodium chloride, are all apt to get into the film under different conditions, and it is found that any of these substances do tend to have a very marked accelerating action on corrosion.If the atmospheric pollution is such as to produce a corrosion product which is deliquescent, so that the film, instead of being thin and invisible, becomes thick and visible, then the corrosion is stimulated to an astonishing extent, and it becomes very serious indeed. that in many cases (e.g. zinc exposed to a damp atmosphere containing hydrogen chloride) the metal does become extremely wet and liquid runs off it. The electrochemical theory does seem to give a reasonable explana- tion of the effects of tarnishing and corrosion ; and although there is reason I have shown in a previous paper 1 W.H. J. Vernon, Trans. Farad. SOC., 19 (1923), 215. 2 U. R. Evans, ;bid., 201.908 ATMOSPHERIC CORROSION to suppose that in some cases, where the film is porous to the reactants, pure chemical action may go on to some extent, yet I am inclined to think that electrochemical action is mainly responsible for the destruction of the metal in the majority of cases. Mr. J. Guild : I am afraid the actual subject matter of this report is very largely outside my own particular purview, and my remarks will be almost entirely confined to the methods of optical testing adopted by the author. As Mr. Vernon points out, the great advantage of the reflectivity test is its extreme sensitivity as compared with other methods when dealing with the initial stages of corrosion.On the other hand, the test, as used by the author, loses from the fact that where the product of corrosion becomes progressively coloured, confusion is introduced in attempting to give a quantitative interpretation to the results. Some of the results are peculiar : for instance, with copper the reflectivity falls to a minimum after a short exposure and then apparently rises again. As far as I can gather, the author explains this as due to a change in the measured component of the reflected light due to its colour, rather than to an increase in the total reflectivity. That may very easily be true : the total reflectivity may continue to fall; but there must be an increase in reflecting power for at least some wave-lengths, namely, those transmitted by the coloured glass used, otherwise the increase shown by the measurements could not have taken place.A mere increase in selectivity without an actual increase in the amount of any of the constituents present in the reflected beam could not produce such an effect. Thus there must be an increase in the actual reflecting power for some wave-lengths at least, and it may easily happen that there is, in fact, an increase in the total light reflected. I think this is quite probable if one considers what is likely to occur in the initial stages of corrosion. I take it for granted that in the first stages the surface is attacked at points and that the principal effect of the corrosion is simply to diminish the total area of unattacked reflecting surface avail- able, and the particles or minute crystals of the product of corrosion merely scatter such light as falls on them, and contribute little or nothing to the reflected light.On the other hand, when the corrosion reaches a certain stage, if the nature of the product is such that it should form, when there is sufficient of it, a more or less continuous skin over the surface, it is quite possible that the light reflected by the surface of this skin may be considerably greater than that reflected by the interrupted surface of unattacked metal which was available for reflecting at an earlier stage. This in itself, I think, produces some evidence-in reply to Professor Carpenter’s query-in favour of the theory that the corrosion on copper is a continuous film. Further, there is even clearer evidence in the nature and graduation of the colour in the case of copper.Mr. Vernon describes the appearance from the edge inwards on a copper plate, and he is merely describing the Newton series of interference colours for films of different thicknesses. I think it is undoubtedly the case that these colours are interference colours, and they can only be formed if there is a film continuous and coherent for areas large compared with the wave-length of light. I t would be advantageous, of course, if the measurement could be con- ducted in such a way as to measure, without ambiguity, the total reflectivity of the surface. At the time Mr. Vernon was good enough to ask my advice in connection with these measurements, flicker photometers for photometry involving colour differences were practically unused in this country.Experience with that type of photometric measurement had beenDISCUSSION 909 uniformly unhappy among photometric workers in this country, largely owing to the fact that the conditions which ought to govern such measure- ments had not been fully worked out. Having had occasion recently to make such measurements, I have been experimenting with a flicker photometer which apparently is almost as sensitive as an ordinary equality of brightness photometer, and I would suggest to Mr. Vernon that in his subsequent reflectivity measurements if he were to substitute for his Lummer-Brodhun photometer a properly designed flicker photometer he could dispense with the colour screen and obtain measurements which really give the total reflectivity of the surface.I have only one thing further to say in connection with that, and that is that in selecting a formula in which to express results it might have given a better measure of the degree of corrosion had the author used some function of the reflectivity of which the terminal values corresponded, as far as possible, to no corrosion and complete corrosion respectively. One terminal value of his present scale is zero reflectivity, which is not, of course, the reflectivity of a completely corroded surface. If Mr. Vernon can get over the colour difficulty and find a function of reflectivity which varies between zero corrosion and something corresponding to complete corrosion, he would then be in a position to see how far quanti- tative significance could be attached to the optical method as compared with the gravimetric method.Dr. J. Newton Friend: Several of the speakers have already men- tioned points to which I should have called attention and I shall be interested to hear how Mr. Vernon is able to answer the queries which these gentlemen have put to him. I would like to associate myself with the congratulations-of Mr. Evans to Mr. Vernon for the very large and patient research which he has carried out. Dr. Bengough has mentioned an interesting thing in his diagram on the board that really anticipates a question of mine; namely, whether Mr. Vernon had attempted to determine the rate of tarnishing on, say, copper after the surface had been prepared chemically. I understand from page 852 that both the polished and the rough specimens were obtained in that condition by purely mechanical means.Now taking copper, supposing that these mechanical means of cleaning were not used but that the surface was prepared by purely chemical methods, it would be interesting to know if comparable results would be obtained with them. I t would appear that if the polishing or mechanical treatment of the surface gives a layer similar to that which Dr. Bengough has found with wet corrosion, then the hiatus in the rate of corrosion which Dr. Bengough predicts in Mr. Vernon’s specimens would not occur if the surfaces were prepared chemically. On pages 859 and 861 there are two sets of curves and in one case- Fig. 7-we have two curves for the dull and polished metal, with the percentage of zinc plotted against the weight increment, and on the previ- ous page the percentage of zinc plotted against the reflectivity.Of course, one cannot strictly compare the two sets of curves because the units are entirely different, but if one were to take pure copper as the standard and call its reflectivity factor 100, and the increase in weight, or surrosion factor, 100, and express all the others relatively thereto, then one might get a direct comparison between the curves in Fig. 6 and the curves in Fig. 7. I have drawn these out, more particularly for series B, which, on page 861, correspond to the weight increment for thirty-six days’ expos- ure, and to twenty-two days’ exposure for series B on page z I, in connection with reflectivity.I t is clear from the accompanying figure that there is910 ATMOSPHERIC CORROSION really a very striking similarity between the two sets of curves, particularly when one remembers that in one case the corrosion has proceeded for more than half as long again as in the other case. That is very interesting and one would have liked to see a reference to Hinshelwood’s recent paper in the Proceedings of the Royal Society. I know that Mr. Vernon is thoroughly familiar with that paper, and it is very interesting to see how Hinshelwood in his experiments has obtained a similar or analogous colour series to those obtained by Mr. Vernon. That leads one to ask whether Mr. Vernon has ever thought of adopting Hinshelwood’s method of determining the rate of oxygen absorption of copper.This method was simply a volumetric one. The copper was placed in a vessel and the diminution of pressure was measured at intervals. The temperature was higher than atmospheric but one would think that, by using a wire of copper or some large surface of copper and a fairly large apparatus, it would be possible to determine the rate of oxygen absorption with a typical atmosphere such as obtains in the “basement.” On page 855 reference is made to the colour effects. 0 10 20 30 40 50 60 70 80 go IOO Zinc per cent. Dr. W. Rosenhain: I have not been able to read the paper as carefully as I should have liked and can therefore say very little about the actual details. The subject of tarnishing of metals, however, is one which every worker who has had to use a microscope for the examination of metals has had to deal with experimentally, although not on a very large scale.One comes into contact with tarnishing phenomena to a more or less painful extent and that has led to certain conclusions which are possibly of interest as bearing upon this work. I n the first place, all metals, with the exception of gold, platinum, etc., tarnish appreciably when in a polished and etched condition, even if kept in a well closed dessicator over such substances as soda, lime and calcium chloride. They do not do it quickly but they do it and they do it in a manner which is characteristic. They do not tarnish uniformly. For instance, a specimen which has been kept in that manner for a certain length of time when examined under a micro- scope, shows patches which are apparently untarnished, and other patches which are quite severely tarnished, and apparently the manner in whichDISCUSSION 911 this occurs depends upon the last substances with which the metal has been in contact.We have developed in metallography methods of washing and drying the surfaces of metals in order to preserve them from tarnishing as long as possible, and the most effective method appears to be to use as nearly as possible anhydrous alcohol, followed by some such substance as ether in which alcohol is freely soluble, but which has a very low solubility for water. The author does not seem to have made any attempt to dry his metals chemically. If the ether is omitted and the metal is allowed to dry from the alcohol, the tarnishing is distinctly more rapid than if the ether is applied before the last of the alcohol has disappeared.The mechanism I am not prepared to discuss but as an observation it is worth noting. An interesting point is the method of measuring the amount of tarnishing. The reflectivity method is a very beautiful one but there are objections to the gravimetric method. There are other possible methods and one is the measurement of electrical contact, i.e. the tarnishing of the surface must interfere with the quality of the electrical contact which occurs under standard conditions, for instance, when allowing a drop of mercury to rest on the surface. With some metals, that would not do at all because unless there was appreciable tarnishing amalgamation would occur. Some other method must be used, therefore, to detect the resistance which the surface offers.Another method is the measurement of the actual thickness of the film, which might be accomplished by interferometer methods. The question of the continuity of the film is interesting but the argument advanced by Mr. Guild is unsafe if we accept the fact that we can get good reflections from a number of discontinuous patches. There need be no uniform continuity throughout the film which, though disconnected in a number of places, would be optically reflective. I am afraid, therefore, that the argument put forward so far as chemical im- permeability is concerned is not conclusive from the optical evidence. The point raised by Professor Carpenter as to the necessity for attacking a problem of this kind from the purely fundamental aspect is a most important one.Exposure to practical conditions, which vary so widely even when they are carefully watched, in a certain location, does not necessarily mean that the behaviour of specimens would be the same in another location. For instance, take the question of the effect of copper in iron, which Dr. Friend will remember very well. I was tempted to test this by exposing plates in various atmospheres. I t was shown that A was better than B in one locality and B was better than A in another, but it was not easy to tell why. There was no doubt that results of such exposure were very variable and although the domestic kitchen for instance might be a domestic kitchen anywhere, it might have quite a different atmosphere say in Portugal or Italy than it would in Scotland.One might be very corroding and the other non-corrosive. The real point I want to emphasise is the one raised by Professor Carpenter, that I. would like to see this matter attacked from the standpoint of scientific fundamental study of oxidation, dry or wet. As for Tammann’s figure of 10l7 years, all 1 can say is, (‘ Where is the experimental proof?” Until he furnishes it I am not prepared to accept these extrapolations because they are very dangerous. That I mean seriously. My final point relates to the condition of the surface. Dr. Friend has called attention to the desirability of test surfaces which have been ckaned chemically. I would feel inclined to suggest the use of etched surfaces in which the polished layer has been removed by etching.WhenATMOSPHERIC CORROSION that is done the results are different from those on a polished surface. There is the well-known fact that stainless steel will not rust readily. The first piece of stainless steel I ever saw was in such a state that we had first of all to file away the rusted surface. The reason was not that the steel was not stainless but that it had been sent in a very rough condition and it rusted. Therefore, roughness is one factor. The question of a cold-worked layer on the surface is another, and in a roughly-filed surface you have both. I hope the work will be continued and that the skill and the patience which has been displayed in this paper will be devoted to the laying of scientific foundations of knowledge on the subject.Dr. G . C. Simpson : I shall only be able to speak from the meteoro- logical and not from the chemical point of view. The meteorological factors which come in I put down as five. There is the chemical composition of the air, temperature, humidity, ventilation and finally there is light. Dealing with the chemical composition of the air, of course there is pollu- tion everywhere, even in the polar regions, and the mist which you see between yourselves and the distant hills is an indication that there is some foreign substance in the atmosphere. I t is certain that sea salt is practi- cally never absent from the air in any part of the world or in any part of the atmosphere in which observations have yet been made.Then we come to temperature. Besides the general effect of temperature, rapid changes must help to break up surfaces and tend to set up corrosive action. There is no method of depositing small particles from the air so good as to have a difference of temperature between the air containing those substances and the surface on which they are to be deposited, therefore changes of temperature in which the air changes at a different rate from the test pieces will have large effects. I can imagine that this may account for a very large part of the difference between the kitchen and the basement. I n a base- ment you have practically no rapid changes of temperature, whilst in the kitchen you have very large ones. Several speakers have mentioned humidity, but they have all spoken about the chemical effect of the film over the test piece, they have not spoken of the mechanical effect of humidity.One mechanical effect is due to the fact that the pollution of the atmosphere is always very hygro- scopic. At all events, there are very large amounts of hygroscopic matter and this attaches itself to all kinds of particles, and therefore the size of the particles varies very greatly with the humidity, even at temperatures a very long way from the dew point. If you have particles or molecules loaded with water they are very much more likely to stick against anything than if they are perfectly dry. That is a way in which humidity may have a large effect. Next I come to ventilation, by which I mean the bringing of more and more air to the samples ; but the effect of this is so very obvious that I do not think I need go into it any further.Then comes light. Lenard in Germany has worked on this subject and found that light-chiefly ultra- violet light-produces in the atmosphere very hygroscopic compounds of nitrogen which are likely to affect these experiments. That is all I really have to say as I am interested only from the point of view of atmospheric pollution. Mr. W. A. Forsyth : I am not a chemist but only an architect, and I thank you for inviting me to say a few words on this subject. I have a great deal to do with medizval structures and in several buildings I know there is some wrought iron which is 700 years old and it will not rust. When it is polished it does not rust.DISCUSSION 913 On the other hand, the unexposed metal which Wren used in St.Paul’s has been rusting very hard and what I fear is that the mild steel which is being used to-day will have disastrous results in a few years time. I am one of those who regard ferroconcrete as a temporary material and I believe, from the nature of mild steel and the composition of concrete, that we shall have failures in the near future. Coming back to the subject of the paper, I am rather mystified at one or two things. Amongst the buildings I have to do with is Salisbury Cathedral and there in the nave are some Purbeck marble columns 60 ft. high, and on the face of these columns are some small attached shafts 10 ft. in length. These are all held to the main shafts with brass rings.They have been there since I 250 and they have not corroded. They have discoloured, but there is no loss apparently by corrosion. They are mostly inside the building. But there are one or two places where these brass rings of the same age are exposed to the atmosphere and these also do not corrode. They are similar but they are substantially the same, after 7 0 0 years, in thickness, as those inside the building. That brings me to this general point concerning copper. If you look at any old church that has window guards of copper, you will see that the wash runs down the wall and although it puts a green colour on the masonry, it preserves the lime- stone better than anything I know. If you look at the Charles I. statue at Charing Cross, the wash from the copper base has so preserved the stone as to keep it in a very fine condition.The same applies to other statues in London and elsewhere and it all mystifies me, I have heard to-night a great deal about corrosion of copper under other conditions, but the cases I have mentioned are matters of interest to architects and I hope you will excuse my raising them. Nothing has been said about the expansion of metals in relation to corrosion. We know what it does in iron but I should like the author of the paper to give information on corrosion in relation to expansion in non-ferrous metals. Mr. C. C. Paterson : It has occurred to me, in listening to the dis- cussion, that this problem lends itself, par exceZeme, to the application of vacuum methods in the testing and examination of specimens. I t has not been mentioned in the discussion, and looking at it as a general research problem, one cannot see how it will ever be possible to get to the bottom of the question unless a fully developed vacuum technique is used in these investigations.‘The whole of such technique is now thoroughly worked out, the pitfalls known and the measuring methods developed. Samples can be suspended one after another in a vacuum and everything controlled in connection with the experiment, i.e. control the temperature of the specimens by using eddy currents from outside, preparing the surface, admitting gases and drawing them off, and generally introducing whatever reagents are desired either in constant streams or otherwise and testing for impurities. When one realises the difficulty of eliminating adhering surface films even at high temperatures in a vacuum, it seems hopeless to know what is happening by working in the presence of atmospheric air, and I would like to know whether any investigators have made a serious effort to attack the problem in the way suggested.I should put it even more strongly than he did and suggest that if real knowledge of the subject is to be advanced, it is the only method. Dr. J. J. Fox (part0 communicated) : The information supplied by Mr. Vernon’s investigation is of fundamental importance, but there are some types of corrosion which have not, so far as I am aware, been Professor Carpenter urged the laboratory method of attack. VOL. XIX-T33914 ATMOSPHERIC CORROSION recorded.Many peculiar cases of corrosion of copper and copper alloys have come under notice and it may be of interest to place on record some of the results obtained in the examination of corroded portions of the metal. I t was found that the copper tape used as lightning conductors on buildings near the sea sometimes became corroded. At the Cathedral of St. Andrews the copper tape had disintegrated at certain spots where the tape touched the stones. The copper conductor was quite normal; it contained 99-73 per cent. copper and the impurities were of the usual character associated with this kind of copper. On examination, the corroded portion was found to contain 4.7 per cent. of constituents soluble in water. This consisted of 3-3 per cent. sodium sulphate and I -4 per cent.sodium chloride. The remaining insoluble part of the incrustation was made up as follows :- Cuprous chloride 40.4 per cent. ; Basic copper carbonate, 53.8 per cent. The basic copper carbonate consisted of 34.8 per cent. copper oxide and 19.0 per cent. combined water and carbon dioxide and the composition did not agree with any simple stoichiometrical proportions of copper oxide, water and carbon dioxide. Obviously the corrosion in this case is due to the combined action of sea water spray and atmospheric carbon dioxide. The peculiar feature was that the corrosion occurred only where the tape was in contact with hard stone, for the part touching mortar was sound. This is perhaps not so surprising as might appear at first for the hard stone was not porous, while the mortar was.In fact, the mortar was found to contain 6.4 per cent. of soluble salts, mostly common salt, with a little calcium and magnesium chloride. The hard stone yielded only 1-4 per cent. of chlorides, mostly sodium chlorides. I t seems reasonable to suppose that the comparative immunity of the copper in contact with the mortar was due to the circumstance that the salt solution was absorbed by the mortar while it would remain on the surface of the stone in contact with the metal. A remarkable case of corrosion was observed when a conductor was held on to a wall by means of gunmetal holdfasts. These corroded at a great rate and within three weeks of being placed in position marked corrosion had taken place at the junction of the holdfast and the conductor.The gunmetal was found to be a leaded bronze and the incrustation con- tained both tin and lead as the examination showed. Composition of Gunmetal Holdfast. I Composition of the Incrustation. Per Cent. Copper . . . 84-81 Tin . . . . 6-06 Lead . . . . 3'45 Iron . . . . 0'14 Nickel . . . . 0.09 Arsenic. . . . 0-40 Zinc . . . . 5-19 Per Cent. Copper oxide . . . . . 44.2 Tin oxide . . . . . 8.6 Chlorine. . . . . . 6.9 Carbon dioxide and combined water 26'1 Lead monoxide . . . ' 3'4 The incrustation also contained some silica and alumina, probably derived from the stones. While it is clear from the nature of this incrustation that the holdfast has been attacked, the peculiar feature of this case is that when strips of the conductor and the holdfast were placed in sea-water and joined up by an external conductor, the copper began to corrode quickly.Little attackDISCUSSION 91 5 of the gunmetal was noticed until later, when a white deposit was seen to form. Some of this peculiarity was due to the condition of the surface, for on cleaning the copper by polishing, followed by acetic acid and ammonia and thorough washing with water, the rate of corrosion of the conductor was slowed down enormously. One other case of the lightning conductor corrosion is worthy of notice. This was found to arise from embedding the earth plate in a bed of coke. The incrustation consisted mainly of basic copper carbonate, but it also contained copper sulphide, and some sulphate was also observed. If coke must be used for this purpose it is desirable to select it as free from sulphide sulphur as possible. As illustrating a little known risk a warning on the use of sulphur to secure metal dowels in position on stonework seems desirable.Some hollow stone pillars were held in position by copper dowels passing down the centre, the hollow being filled in with a mixture af molten sulphur and clay. In a comparatively short time some of the pillars developed large cracks and on examination it was found that the dowels were badly corroded, The incrustation consisted of basic copper sulphate and in this case the origin of the corrosion is clear enough. The incrustations due to corrosion of bronze on public monuments are generally found to consist of basic copper salts, frequently with a large pro- portion of carbonate.This suggests that when the corrosion has sta!ted, its progress will be materially hastened by atmospheric carbon dioxide. Of the impurities present in town air likely to initiate corrosion, it would be interesting to ascertain whether the traces of ammonia and the ever- present minute proportion of oxides of nitrogen are to blame. I t is also quite likely that the small proportion of oxides of sulphur in the atmosphere plays a part in attacking the zinc of brass monuments in exposed situations. The unsightly appearance of so many of our stone monuments which bear bronze figures or inscription tablets is witness to the destructive effect of the town atmosphere. I t is rather surprising to learn that the incrustation of basic copper salts which disfigure the stones is considered to possess some value in preserving the stone. I t has been stated that the supposed excellent state of preservation of the stonework of King Charles I.’s statue at Whitehall is due to the copper salts derived from the bronze.While there is no doubt as to the greenish appearance of much of this stonework there is little evidence of preservative action. The carved stone is full of the black incrustation which in similar cases in London we have found to consist largely of hydrated calcium sulphate, and it is a typical example of destruction of stone by sulphur compounds in the air. As a matter of fact it is preferable, especially with the newer work, to prevent the drippings from bronze discolouring the stone. This may be secured by coating the bronze with two coats of a thin matt copal varnish or tung oil varnish and renewing the coatings every few years as required.Mention may be made of the liability to corrosion of copper alloys in contact with halogen compounds such as carbon tetrachloride, especially when these are impure. Traces of ammonia are sufficient to induce ex- tensive corrosion, as shown by H. W. D0ughty.l Carbon disulphide is also under suspicion in these compounds, a matter of considerable importance, having regard to the widespread use of carbon tetrachloride in fire extin- guishers which are constructed of brass. Dr. W. C. Reynolds said he was interested in two phases of the 17. Amer. Chem. Soc., I g I 7 , 3 , 2685.916 ATMOSPHERIC CORROSION atmospheric corrosion question.As regards metals his experience was con- fined to mercury, which presented interesting features. He had traced the great difference that existed between published determinations of its sur- face tension, to the presence of a film of mercurous-hydrate on its surface, which formed with almost incredible speed on exposure of a fresh surface to air. Mercury (purified by agitation with dilute nitric acid, and distillation in vacua, and subsequently treated by the Harries process) was found to be hygroscopic, as can be demonstrated by allowing it to fall in a stream of fine globules from a separator, terminating in a capillary, down a wide tube, closed by a narrow siphon delivery, through which a stream of moist carbon dioxide is passed. The coalescing droplets are soon surrounded by a collar of liquid water, in the restricted delivery.If the carbon dioxide is replaced by air, the water collar is associated with a film of mercurous hydrate. When purified water, mercury and oxygen are agitated together in a bottle mercurous hydrate is formed, the amount increasing until the satura- tion point of the water is reached, as can be followed by examining portions of the water colorimetrically with sulphuretted hydrogen in a tintometer. After saturation occurs oxidation proceeds very slowly, unless the quantity of water is relatively small, the air space very large, and the mercury is very violently agitated for some time when appreciable quantities of the hydrate accumulate. I n the presence of a chloride, calomel is formed as a secondary product as it is less soluble than the hydrate.The reaction occurs, although ex- tremely slowly, in the presence of dilute alkali, which appears to indicate that carbon dioxide does not play any part in the phenomena, which seems to be represented by the equation 2Hg i H,O + 0 = 2HgOH. The phenomena of the dropping electrode investigated by Paschen and others, proves that oxidation occurs in a minute fraction of a second. Possibly some other metals are first attached in this manner, and the re- action product, by interaction with the oxides of sulphur, nitrogen and car- bon present in the air, is subsequently transformed into more complex substances. The peculiarities of mercury surface phenomena had led him to investi- gate some of the variable gaseous constituents of the air quantitatively, both in London and in the country.He found that London air, apart from ex- ceptional conditions such as very severe fogs, or wind of storm velocity, contained I volume of sulphur dioxide in from 2 to 16 million volumes of air, the proportion naturally being least in summer. At the village of Up- minster, 1 7 miles from Charing Cross, it was generally about a quarter of this. In contact with liquid water the sulphur dioxide is instantly oxidised to sulphuric acid, by the ozone, which in London appeared to rarely exceed the proportion of I volume in from 18 to 28 million volumes of air, and which in winter curiously seems to exceed the proportion in the surround- ing country, possibly due to the strong convection current of warm air causing greater intermingling with richer upper air layers over the Metro- politan area.Nitric acid and oxides of nitrogen are generally assumed to be formed in the upper air, but his measurements indicated coal combustion as the source of a large proportion of it, because he generally found quite three times as much in London as in country air, and the proportion in both in- creased in winter. He had not found as large a proportion present as Dr. Fox, his measurements hardly exceeding I volume of nitric acid vapourDISCUSSION 917 in 5 0 million of air in London. There are, however, admittedly special difficulties attached to the rapid complete absorption of the oxides of nitro- gen. He agreed with the previous speakers in thinking that these impurities must play at least an important secondary part in atmospheric corrosion.Dr. R. Lessing: There is one point I should like to mention, although not bearing directly on atmospheric corrosion, and I mention it because of Professor Carpenter's plea that the inquiry should be broadened. I am referring to corrosion in gas mains and service pipes. The conditions there, being of a reducing character, are quite different from an atmospheric corrosion, although it is not unlikely that the very small amount of oxygen in town gas, which amounts to something like Q per cent. by volume, plays an important function. This corrosion is becoming of late years of eriormous importance to gas undertakings and the causes of it have not at all been recognised. We have here practically all the impurities that have been mentioned in the paper to deal with and in addition hydrocyanic acid, carbon disulphide and other sulphur compounds, carbon dioxide, etc., and over and above all these there is the influence of hydrocarbons.I t has been claimed that the leaner gas made of late pears is responsible for this corrosion inasmuch as it does not protect the iron pipes as efficiently as the heavier hydrocarbons, which formerly used to be there in greater quantity. One point appears to be established, however, with absolute certainty, and it is that steel mains are rather more liable to corrosion than are cast iron or wrought iron mains. The whole question is very much wrapt in mystery and little really useful research has so far been carried out.I thought it would be well for those who have to deal with purely atmos- pheric corrosion to bear these facts in mind because after all they may give some clue as to what happens in the other case. Mr. Edward H. Hall: With regard to Mr. Vernon's experiments on the tarnishing of silver, the following observations may not be without significance. I t has been noticed that when ordinary silver plate is cleaned with a powder, e.g. chalk applied wet, the silver is easily wetted : on repolishing, the process can be repeated, but after a few such treatments the wetting fails. On allowing the specimen to stand overnight, however, it once more becomes capable of being wetted by the powder and water. Similarly, a surface deliberately greased and the grease then rubbed off as completely as possible with a clean rag, although not capable of im- mediate wetting, becomes so on standing overnight.Moreover, of the two surfaces, the relatively non-greasy one, after being cleaned and polished as described, tarnishes at a more rapid rate than the other, and withstands six or seven consecutive repolishings before it refuses to be wetted, as contrasted with two or three in the case of the presumably more greasy surface. I t is obvious that a change in the silver surface has taken place in both cases, intimately connected with surface tension, possibly by the adsorption of a film of moisture. In considering Mr. Vernon's results for silver, the relationship between initial reflectivity and percentage reflectivity losses are suggestive. Thus considering the polished surfaces of fine silver, special standard, and standard silver respectively, we have (Table IX.) :- and similarly for the corresponding reflectivity losses 93'5 > 84.0 > 81'5 75'0 > 53 > 46-ATMOSPHERIC CORROSION If it can be admitted that the initial reflectivity is a measure of the completeness of the “Beilby film,” the formation of which is intimately connected with the surface tension of the metal, it may be that the above figures indicate the bearing of surface tension on tarnishing, in so far as the condensation of aqueous or greasy vapours on to the silver is connected with the surface tension of the particular surface exposed. In this regard it is not without significance that those surfaces which have been dulled by emery, and which do not therefore possess the “Beilby film,” have been practically reduced to the same level by the emery both as regards the rate and nature of the tarnishing : in such cases surface tension per se would be outbalanced by the tendency of the capillary channels and edges formed by the emery, to promote condensation of vapours .The anomalous behaviour of the copper specimens in the kitchen ex- periments suggests to Mr. Vernon that greasy vapours are present. If this be so, there will probably be a balance between the condensation of greasy vapours and aqueous ones, the final equilibrium depending, at least to a certain degree, on the surface condition of the silver. I t is not unreason- able to suppose that the greasy vapours have a protective action and the aqueous a tarnishing one and it is possible that the “fogging ” effects are also connected with grease, the more intimate contact necessary for true tarnishing being prevented by it.I t would be interesting to know whether any indication of a systematic difference in, say, contact angles between the various silver surfaces and suitable liquids could be detected. As regards the slight differences in reflectivity and weight increments between dull polished and bright polished coppers and brasses, has the increase in intrinsic surfice, brought about by the abrasion of the emery, any bearing on the point ? I t has often been observed that signs gilded with “gold leaf” and ex- posed to the outside air, display a marking which renders it easy to trace the application of the “gold,” leaf by leaf, the centres of which are com- paratively untarnished whilst the edges are somewhat discoloured, the transition being gradual. Is there any relationship between this effect and the more rapid rate of corrosion at the edges of brass plates observed by Mr.Vernon? Dr. B. S. Evans (communtated): It is well known that sulphur dioxide solutions will react with metallic copper causing a film of copper sulphide, but the conditions under which this happens do not appear to be so well known. If a slip of bright copper is placed in a solution of sulphur dioxide it will remain bright indefinitely. If, however, a relatively small amount of a chloride is added the copper turns black in a very few minutes: the case appears to be exactly parallel with that of arsenic, antimony and bismuth investigated in my paper on the Reinsch test.1 Some experiments were carried out to test the possible bearing of this on atmospheric tarnishing.A solution of sulphur dioxide was placed in each of two flasks and strong hydrochloric acid was added to one of them, a slip of bright copper was suspended in each by being passed into slits in the corks which closed the mouths, the copper slips being out of contact with either the liquid or the glass; the slip in the flask containing hydrochloric acid darkened promptly and at the end of half an hour was coated with a dark brown film, strongly resembling that obtained Analyst, Sept., 1923, p. 4x7.DXSCUSSXON 9’9 after long exposure to the air; the slip in the other flask remained bright. In another case where wet slips were used the action was more rapid and violent but the result was the same.Into three similar flasks strong sulphuric acid was placed. Sodium sulphite crystals were added to one, sodium chloride to another and a mixture of both to the third, and copper slips were suspended as before. In this case the results were somewhat similar to those of the first experiment. The L‘ sulphite ” copper remained bright. ,, “ chloride ” ,, tarnished slightly. ,, ‘‘ mixed ” ,, tarnished somewhat more. The action was, however, many times slower than that in a moist atmos- phere, taking hours, instead of minutes, to reach the same stage, and after a time ceased entirely. This seems to show that moisture is necessary to this particular reaction.It is noteworthy that the film produced by sulphur dioxide is of the same type as that which the author found to be formed under “kitchen ” conditions-red initially and passing gradually to a dull brown without showing any of the interference colours displayed, for example, by the films formed by the action of sulphuretted hydrogen. The fact that two reagents are necessary to this type of tarnishing, i.e. sulphur dioxide and chlorides, would tend to explain the fact that puzzling and perhaps somewhat contra- dictory results were sometimes obtained. I t is necessary to be guarded in drawing conclusions from the velocity of film formation on the surface of copper; in the Reinsch investigation two samples of copper foil were found which gave identical velocity curves in the case of antimony and distinctly different, though parallel, ones for arsenic; the degree of purity of these samples seemed to be the same and no other difference could be detected in them.Mr. E. A. Bolton wrote that he had read the paper presented by the author with very great interest as it opened up a very important and com- paratively new line of research. The author was to be congratulated upon the methods of attack chosen and upon the conclusions reached. The similarity between some of the results obtained by the author and those of Pilling and Bedworth was very striking and the discovery of a third type of curve, as in the case of iron, was of much interest. He would like to ask whether, in this instance, any connection could be traced between the areas of initial attack and the microstructure of the sheet.He would point out that at higher temperatures iron tarnished in the same way as the non-ferrous metals by forming continuous films. Of particular interest were some of the experiments described in Part 11. in which it was observed that specimens placed in a stream of air (treated in various ways) became tarnished very quickly at the end nearest to the air inlet. I n some experiments carried out at about 650’ C., where specimens of brass were heated in a stream of purified and dried carbon monoxide, a similar phenomena was observed. In some cases the specimen became dull and tarnished at the edge nearest to the gas inlet, while the rest of the area remained bright. He had recently observed a case of ‘‘ fogging ” of nickel similar to that described in page 881.A nickel plated article which had remained practi- cally bright for a considerable period developed fogging very rapidly upon the advent of a spell of cold weather. He would suggest that some interesting results might be obtained by the extension of the ‘( field ” tests to include some other types of atmosphere920 ATMOSPHERIC CORROSION such as that of an analytical laboratory and that of the casting department of a brass works. He would be interested to know, though that was probably outside the scope of the work, if the author had any experience as to the retarding or accelerating influence upon tarnishing of previous pickling or dipping treatments. Mr. Harry C. Lancaster (communicated) : The author’s report covers a good deal of ground on an exceedingly complex subject and one which is of great commercial and national importance.Bearing in mind that although much attention is being focussed in the endeavour by various means to prevent corrosion, the study of means to increase it may also be regarded as of considerable importance. It may be recalled that the consumption of white lead, a product whose manufacture depends essen- tially upon a corrosion process, is 50,000 tons per annum in the United Kingdom alone. The author only deals, it is true, with the early stages of tarnishing and corrosion, but probably the initial stages are the most important, and one would naturally like to see these tests greatly extended, especially on the laboratory side, for it is conceivable that with an extension of time, results and conclusions might be greatly altered.The question of impurities (Table lIL, p. 864), is of great interest but one would have liked to have had a complete analysis of these three zincs. Is the difference in corrosion due to the question of purity? And if so, is the electrolytic zinc the purest of the three? At one time it was generally thought that the purest zinc was the most difficult to dissolve in acids, but Mr. W. G. Rigg, late of the New Jersey Zinc Company, states that the purest zinc1 they have produced for the United States Bureau of Standards was almost explosive under acid treat- ment, or in other words the rate of solution was exceedingly rapid. If then this electrolytic zinc was the purest in the test, there would seem to be some connection between atmospheric corrosion of the zinc and the rate of solu- tion in acid.There may, however, be no connection between the rate of solution of zinc in acid, and atmospheric corrosion, but this most certainly is the case with lead. The greater tarnishing of emeried and dull surfaces (pp. 840, 841, 843 and 883), conforms with expectations and emphasises the advisability of keeping all rolls highly polished and surfaces perfect for rolling all sheet metals. The reference to hardness (pp. 878 to 880) indicates my objection to hammering the test plates ; the setting up of strains which bring about surface alterations. It might be of interest to state that rolled zinc angles when used in economiser tubes gradually corroded but maintained shape and form until the last portion, whereas extruded angles of like quality under similar con- ditions broke up and disintegrated entirely.The President : I will not take up much time myself, but I should not like to appear to be wanting in appreciation of the large amount of work which has been done in getting this report together, and of the in- genuity displayed. At the same time the note that Professor Carpenter struck at the beginning of the discussion appeals to me very strongly. It comes to this, that the chemical side has not received such weight as it is Why should the test plates have been hammered? Prepared by redistillation, and selection of the distillation fractions. Analysis : Iron, 0~004 per cent.: Lead, less than 0.003 per cent.; Arsenic, less than 0-0001 per cent. ; Cadmium, not determinable.DISC USSXON hoped will be the case in the future. The chemist would like to know more about the composition of the films. There has been for example little attempt to differentiate between sulphide and oxide, nor among the pro- ducts of interaction with other impurities in the atmosphere. The number of variants that are present make it necessary to carry on laboratory work with known simple constituents. Further information is required as to what the substances in the atmosphere are that may induce corrosion. We know, of course, of the frequent presence of sulphuric acid, because of its effect on limestone. We have just heard that the determination of NO in the air is going on evidently in two directions, but I do not think the presence of that NO is entirely due to electrical causes.We have evidence that it arises to a considerable extent from burning flames. The proportion is considerably more, I think, than has been recognised before simply because our methods of determination have become more refined. As it is now so late, I will call upon the author to deal with the points that have been put to him. Mr. W. H. J. Vernon (in rep@ to the discussion) : The author desired to express his gratification that the paper had elicited so many interesting and valuable contributions, especially in view of the circumstance that practically all possible viewpoints had been authoritatively represented. He believed he was correct in suggesting that the only serious criticism to be met (apart from one instance involving purely theoretical considerations) was that which had reference to the position of the “laboratory experi- ments ” in relation to the (‘field tests,” and inasmuch as this question was common to the remarks of several speakers he would deal with it at once.Whilst it would no doubt be appreciated that the present report was more or less in the nature of an interim communication, he would like to point out that this was more especially true in the case of the section devoted to ‘‘ laboratory experiments.’’ At the time that the bulk of the “ field tests ” were launched the amount of time and attention that would be involved was certainly not anticipated, with the result that it had not been possible to develop the purely laboratory side to the relative extent that had been intended. Since, however, certain definite results had emerged from the work as a whole, it had been thought opportune to recommend its publi- cation at the present stage.He was glad that several speakers had endorsed Professor Carpenter’s advocacy of greater attention being devoted to labora- tory methods in subsequent work, and he could assure them that experi- ments of that type would be at least as congenial-and probably more fruitful of immediate results-than the so-called c c field tests.” Nevertheless he was bound to add a word in justification of those tests. In the first place he felt that to some extent they laboured under the disadvantage of a mis- leading title.Actually the term had been used as a convenient substitute for the more awkward title “Tests carried out with specimens exposed in situ to the atmosphere concerned ” ; in view of the close observation under which the tests had been conducted-in some instances indeed in the ‘‘ laboratory ” itself-they might well claim to be true laboratory experiments. The term normal tests would probably have been more appropriate to the case. (Incidentally it might be pointed out that both the gravimetric and optical results, upon which several speakers had been good enough to comment in favourable terms, had been obtained entirely in connection with these “field tests.”) On the other hand, the term ‘( Laboratory Ex- periments” in contradistinction to the above, could be interpreted as meaning “Tests carried out wholly or in part under artificial atmospheric conditions.” He suggested therefore that in so far as he had used or was922 ATMOSPHERIC CORROSION about to use these terms, the above distinctive meanings might be attached to them.He desired next to emphasise that in atmospheric corrosion one had to deal with a medium of extraordinary complexity, so that it became eminently desirable, even before starting any purely laboratory work at all, to observe systematically the effects actually produced upon metal surfaces exposed to the atmosphere as one found it. Without the information so obtained one might work for a considerable time with synthetic atmos- pheres, and obtain results which-while probably of great theoretical interest -could not be correlated subsequently with results actually obtained in practice.The difficulty of obtaining results capable of practical interpre- tation in, say, synthetic seawater was notorious; he ventured to suggest that the difficulty in the case now involved was even greater. He sub- mitted therefore that the results recorded in Part I. of the present report would be of value as a guiding, and to some extent as a restraining principle, in pursuing the work upon the lines which had been advocated, and with which he personally entirely agreed. Turning now to individual contributions, the remarks which Mr. Munby had been good enough to make were opportune in that they provided an historical introduction which was lacking in the report itself.Professor Carpenter had not only given a most valuable lead to the discussion on the scientific side but he had raised several specific questions of a very searching character. With regard to the tarnish film upon copper, evidence as to its con- tinuous character appeared to lie in two directions. On the one hand there was the indirect evidence of the parabolic shape of the weight-incre- ment curve; i.e. it wag somewhat difficult to see how the initial film could affect the subsequent action in the way it did unless it were assumed to take the form of a continuous envelope. More direct evidence was obtained by the use of the microscope, in this case, however, with obvious limitations. A surer indication appeared to be afforded by the progressive display of spectrum colours, which evidently could only be due to inter- ference or diffraction phenomena.Hinshelwoodl in his work upon the study of copper films formed by alternate oxidation and reduction, stated that the colour films produced on oxidation were diffraction effects con- nected with a minutely granular structure. In this case clearly, the degree of discreteness must be of an order comparable with the wave-length of light. In the author’s results, however, it appeared more reasonable to suppose that the colours were true interference colours (as advanced in the present discussion by Mr. Guild, who had, indeed, supplied a most interest- ing reply to Professor Carpenter’s query) a view which postulated a trans- parent film of an even greater degree of continuity. With reference to the straight line curve given by zinc (in the unsaturated atmosphere) the shape of the curve would doubtless sufficiently testify to the permeability of the scale, whilst if negative evidence could be accepted, the absence of interference colours would indicate that the film was not continuous.Direct evidence was difficult on account of the similarity in colour between the scale and the metal. The question of the relationship existing among the different types of curves, raised an interesting point. The shape of curve “No. 3 ” (iron) appeared to be capable of a two-fold explanation. According to Friend’s theory, acceleration in the rate of corrosion was due to the chemical activity of the scale (intimately connected with the dual valency of iron).In the light, however, of the electro- Proc. Roy. SOL, A, Vol. 102, 1922, pp. 318-28.DISCUSSXON 923 chemical view first advanced by J. Aston,’ the hindrance imposed upon access of oxygen to the underlying metal, caused areas covered by rust to become anodic to the surrounding uncorroded metal. Applying these views to curve “No. 2,” either the scale was merely chemically neutral (on which explanation no information was afforded as to its degree of dis- continuity) or conditions were such that electrochemical action did not take place. In the latter connection it was significant that the straight line curve was invariably associated with conditions of unsaturation with respect to water vapour. Incidently, support for the electrochemical view appeared to be afforded by the fact that under conditions of greater relative humidity (iniermittently reaching saturation) the curve for zinc followed partially in the direction of the iron curve.Conversely, if this explanation were correct, one was led to the conclusion that the scale which formed upon zinc (in a humid atmosphere) whilst not quite continuous, was relatively compact, in contradistinction to the case of iron where one had discon- tinuity upon a gross scale. Concerning the question of sulphur compounds, whilst he had men- tioned H,S and SO, as the obvious constituents, he had at the same time appreciated the possible influence of less obvious products of pollution, which, as Professor Carpenter had pointed out, might well include organic sulphur compounds.So far, however, he had only experimented with thiophene (to the study of which he had been led quite indirectly) and although under certain circumstances this substance yielded very striking results,2 from the present point of view it appeared to be without influence. With regard to the “fogging” of nickel and the production of the “smoky film ” upon the brasses, he regretted that he had no further in- formation to add to the observations recorded in the report. He agreed, however, that the further investigation of these phenomena was highly de- sirable, and he hoped to be in a position to undertake more intensive tests in the near future. The emphasis which Professor Desch had laid upon the three main types of superficial attack was of special interest in view of the many valuable observations which had been made by that authority on the subject of the influence of the corrosion product.Professor Desch also called attention most usefully to the important part which might be played by climatic conditions in determining the physical characteristics of the corrosion product. With reference to the vexed question of mechanism, the author ventured to suggest that in the well-defined cases of electro- chemical action under atmospheric conditions the evidence led to the con- clusion that electrochemical phenomena came into operation subsequent to the formation of a certain amount of scale by ordinary chemical processes. With regard to the term ‘( surrosion ” the author had to confess that he entirely failed to see in what respect the word was ugly; at the same time he felt no doubt as to its utility.Presumably (since justification could be adduced from the dictionary) no exception would be taken to the use of the word “erosion” to denote “such corrosion as that induced by acids, a more or less soluble product resulting, exposing the underlying metal to further attack.”3 I t would appear somewhat illogical, however, to admit a special case where the corrosion product was continually removed from the metal surface, and to deny it where the corrosion product remained in sifu, which was the state of affairs envisaged by the word “surrosion.” Inter- Trans. Amer. Electrochetn. SOC., 29 (1916), 449. Vide W. H. J. Vernon, in discussion on paper by U. R. Evans, J. Inst. Met., 30 (tg7hewton Friend, “ Carnegie Scholarship Memoirs,” IX (1g22), 2.924 ATMOSPHERIC CORROSION mediate cases would doubtless be found, but that could hardly detract from the value of the expressions of which there were so many well-defined examples.Curiously enough, the atmospheric rusting of iron, in connection with which the term surrosion had originated, appeared to approach very closely to such an intermediate case. On the other hand, phenomena such as the tarnishing of copper at ordinary temperatures and the oxidation of many metals at more elevated temperatures, whilst bound ultimately to be in- cluded under the general heading of corrosion, presented features which very clearly distinguished them from corrosion in the more popular sense of the word-i.e. that sense in which the term ‘‘ erosion ” was synonymous. The author could not agree that there was any familiar existing word which adequately described the former process.Apart from any question of euphony the word ‘( rusting ” appeared to be too intimately associated with iron to serve the general case, whilst “ tarnishing,” involving as it did the idea of colour changes, was difficult of application to metals like zinc and aluminium where a considerable amount of oxidation could take place with very little alteration in appearance. Whilst the author would continue to use these terms in the same way as heretofore, his own experience with the phenomena involved had convinced him that the word surrosion (in the sense in which it had been used in the text) did actually serve a most useful purpose.He desired therefore to make a special plea for its inclusion in scientific terminology. With regard to the question of any correlation between impurities in the metal and amount of corrosion, so far as the work at the present stage was con- cerned the answer was largely in the negative. Certainly in the case of copper the effect of impurities had been extraordinarily inconspicuous. Zinc in the unsaturated atmosphere had also given no indication of any appreciable influence of impurities, and although under more humid conditions there was some slight indication of the most impure material yielding the greatest surrosion, the author would not like to commit himself to a definite state- ment at the present stage. I t appeared to be significant, however, that in the case both of zinc and of copper the type of weight increment curve obtained was not influenced at all by the degree of purity of the metal.In this connection Dr. Bengough might possibly care to note some of the author’s remarks in reply to Professor Carpenter. With reference to the scale on zinc functioning in a neutral instead of a protective capacity, this result was certainly contrary to the prevailing impression and had occasioned the author himself no little surprise. I t was significant that whilst the protective character of the copper scale had emerged so con- clusively from the present tests, no evidence whatever had been found for a like process in the case of zinc. At the same time it was important to note that this statement was based entirely upon observations in indoor atmospheres; (open air tests were in progress, but had not yet reached a stage when conclusions upon this point could be reached).I t was generally assumed that zinc exposed to the open air became covered with a layer of basic carbonate which largely protected the underlying metal from further attack. In the absence of excessive atmospheric pollution, that view appeared eminently reasonable, and might well be correct (although so far as the author was aware there had been no definite experimental proof). Nevertheless it might be pointed out that the behaviour of zinc in practice was usually observed relatively to that of iron, as a protective covering for which it was so largely employed. Considering the relationship existing between the behaviour of the two materials as illustrated in Fig.23 (B) it ‘ was easy to see how, from the mere failure to appreciate the enormously Dr. Bengough had raised a number of very interesting points.DISCUSSION 925 accelerating nature of the attack upon iron, the impression might be gained that the attack upon zinc slowed off with increasing time. With regard to the uniformity of the scale upon zinc and copper, the author had dealt with that point to some extent in his reply to Professor Carpenter. He desired to emphasise, however, that what he had said about the uniformity of the tarnish film upon copper referred to the early stages. Subsequently evidence of discontinuity made its appearance at points distributed irregularly over the surface.The effect was not very apparent to a casual observation ; under a low power of the microscope, however, the appearance at each of these points was remarkably similar, taking the form of a dark central nucleus with alternately light and dark concentric rings. I t was of great interest to note that this phenomenon was very similar to that which had been observed by Bengough and Hudson for copper and brass exposed to distilled water, as recorded in the Fourth Report to the Corrosion Committee of the Institute of Meta1s.l The present author had recently taken a photomicrograph of one of the small areas referred to above and on subsequently looking up the Fourth Report he had found illustrated therein 2 an almost exact replica of this photograph (at approximately the same magnification), representing 70/30 brass after 14 days’ exposure to distilled water.(Here again the effect had developed in a previously uniform scale.) In each case one had a central nucleus with four well-defined rings, recalling very strikingly the Liesegang ring phenomenon. I t should be stated, however, that in the author’s work the appearance of these L4spots ” in no way effected the disposition of the weight-increment curve (at all events for comparatively long periods) the rate of attack continuing to fall off in the same way with increasing time. This, of course, did not preclude the idea of the acceleration going on at these points, but it did indicate that if such a process went on at all it was insignificant compared with the protective influence that was still exerted by the tarnish film as a whole.Dr. Bengough’s concluding point was also of great general interest. To the author it appealed most strongly on account of the prediction which Dr. Bengough had made, which appeared actually to have achieved fulfilment in recent events. In connection with the tests which were being conducted upon the roof of the Royal School of Mines building, it had lately been observed that certain of the specimens were exfoliating; closer examination showed that the phenomenon was confined entirely to the plates of 70/30 brass, which presumably was also the composition of the drawn tubes to which Dr. Bengough had referred. Whilst it was too early to speak at all conclusively there would appear to be little doubt that the two phenomena were intimately connected.The author would certainly follow any subsequent developments with all the greater interest in view of Dr. Bengough’s most opportune contribution. Referring to the ‘( benzene experiment,” inasmuch as this had been the means of eliciting a contribution from Mr. Evans, the author certainly did not regret its inclusion in the report ; he frankly admittted, however, that his own conclusions from this experiment had probably been unduly empha- sised, and consequently he could not complain that they had received so large a share of the attention of Mr. Evans. Professor Desch and Mr. Evans had both questioned the dryness of the benzene; this criticism was obviously impossible to meet, and it would indeed appear futile to prosecute further inquiry along such lines.This was a matter for very little regret. It was to be expected, quite apart from any question of dielectric constant, J. Inst. Met., 21 (1919). 2 Ibid., Photo go, Plate 24 (facing p. 145).926 ATMOSPHERIC CORROSION that benzene vapour would be much less effective than water vapour in accelerating the action at the metal surface. Furthermore the views of the author were entirely independent of the results of this particular experi- ment. Whilst recognising that electrochemical principles were applicable over a wide range of corrosion phenomena, the author maintained that there were familiar cases-such for example as the tarnishing of copper at ordinary temperatures-where the mechanism consisted in simple chemical attack; it was this latter respect that Mr.Evans and himself did not “see eye to eye.” The figures due to Tammann which Mr. Evans had quoted would appear to be quite irrelevant to the point at issue (perhaps fortunately so in view of the difficulties in the way of experimental verification !) since they were concerned entirely with the relation between metals and oxygen. Otherwise the implication was that the removal of water vapour from the air of ordinary workaday life left oxygen as the only active constituent; this quite naturally was not the impression which Mr. Evans intended to convey, and certainly the architects would not be under any such mis- apprehension. The author had shown (p. 895) that air from which the soluble impurities had been removed by washing, but containing water vapour almost to the point of saturation, was without visible influence upon copper.Considering, however, the relationship between copper on the one hand and air highly charged with hydrogen sulphide on the other, he had demonstrated that drying the materials separately for several weeks over phosphorus pentoxide did not prevent action taking place compara- tively rapidly on bringing together in an enclosed space. The action moreover proceeded continuously whilst the system was still in this excessively dry condition, producing, after several months, considerable exfoliation of the scale. (The H2S received a preliminary drying over calcium chloride, and no visible change was produced upon the PzOB during the period of the experiment.) As to the acceleration of the process by the presence of water vapour (concerning which experimental fact Mr.Evans and the author were in agreement) the author had no intention of attempting to dispute the general view (to which Professor Desch had alluded) that perfect dessication would inhibit the action of any gaseous system upon a metal surface at ordinary temperatures, and he agreed there was good reason to suppose there would be no action. H e would point out, however, that this might well mean no more than did the inhibition of the action between NH, and HCl by desic- cation of the materials, which was among the best known of Professor Baker’s results. Apart from the conception of anodic and cathodic areas upon a sufficiently minute scale in the metal surface (a conception which Mr.Evans apparently did not think necessary to justify) Mr. Evans’ case depended upon the assumption that water must necessarily act as an electro- lyte. Such an assumption was not essential to the explanation of the process, and the author had suggested that water might act as a catalyst. He still thought that the suggestion was a reasonable one, and certainly could not agree that it was in any way inconsistent with the explanation of the falling off in the rate of attack with increasing time as indicated by the parabola connecting weight-increment with time. H e would remind Mr. Evans that whilst the shape of the curve was determined by the increasing thick- ness of the corrosion product, the rate constant was determined by quite other causes, and it was in this latter direction that a catalyst might be ex- pected to act.I t was well to bear in mind that Pilling and Bedworth’s results were obtained entirely with oxygen (or air) as the gaseous medium, in which instance they found that water vapour had no accelerating effect. On the other hand, with copper and hydrogen sulphide (in the presence ofDISCUSSION 92 7 air) one had a reaction which was accelerated by the presence of water vapour, so that it was difficult to draw an exact parallel. The author trusted that it was not necessary to affirm his faith in the reality of adsorbed films on metal surfaces, and he regretted if any fault of expression in the text had conveyed a contrary impression. He certainly could not agree, however, that at temperatures well above the dew-point one had to deal with films of such gross magnitude as Mr.Evans’ reference to the use of the desiccator would appear to suggest. (Water taken up by hygroscopic materials was obviously quite another matter.) The author would further point out that the view which attributed the functions of an electrolyte to the very thin film of adsorbed water molecules was not merely unnecessary as indicated above, but was actually contradictory to available evidence. Thus, in the case of copper and iron respectively exposed under identical conditions above the dew-point, one found that the copper tar- nished rapidly whilst the iron remained perfectly bright. Under conditions of saturation with respect to water vapour, however, the results were com- pletely reversed, the copper then being comparatively unaffected during such time as a considerable degree of rust was produced upon the iron. Considering the state of affairs above the dew-point, the question might well be asked, if it were the adsorbed film of moisture which brought about the tarnishing of the copper (electrochemically), why did it not function in a similar manner upon the iron surface? The converse was obvious.There would thus appear to be inconsistences in the service which these adsorbed films rendered to Mr. Evans’ “ evil purposes ! ’’ If, however, the view be accepted that the rusting of iron was an electrochemical (or electrol lytic) phenomenon, in which liquid water played a primary and essentia- part, whereas the tarnishing of copper was a simple chemical phenomenon brought about by a reaction between gas and metal, water playing a secondary part, then such inconsistences would immediately disappear.There was one remaining point in Mr. Evans’ remarks which called for reply. Referring to the parabolic curve which he had obtained for copper the author’ had advanced this as evidence that the mechanism was similar to that in the high temperature oxidation involved in Pilling and Bedworth’s curves. Whilst he had omitted to draw this conclusion in the present paper he gladly took the opportunity to rectify the omission. He still maintained that it constituted legitimate and quite valuable evidence as to the chemical nature of the process. I t was surely far easier to reconcile the shape of the curve (together with the other evidence as to the continuity of the film produced) with the purely chemical explanation than with the electrochemical view postulated by Mr.Evans. Indeed, on the former view that evidence was to be expected; the author ventured to suggest that the same could not be said of the latter. In conclusion, if the author might be permitted to dwell for a moment on the more general problem, he would suggest that Mr. Evans’ views would be capable of wider application if the stress were laid upon the “ electrolytic ” rather than the “ electrochemical ” aspect. The former heading would of course include all cases where the presence of an electrolyte, functioning as an electrolyte, was necessary for corrosion. The latter term, although in the past frequently employed synonymously with the former, appeared now to be definitely associated with the special case where one had, as an additional essential, spatial division of the metal surface into anodic and cathodic areas.Whilst there was a considerable amount of evidence which could be ranged against the hypothesis that corrosion as a whole was entirely electrolytic in character, the author could not see how the most Trans. Farad. Soc., 19 (1923)~ 215.ATMOSPHERIC CORROSION ardent electrochemist could maintain the purely “electrochemical” view. In the discussion on Mr. Evans’ Manchester paper (a contribution of acknow- ledged importance) the present author had asked Mr. Evans whether he considered that the production of sodium or potassium in a perfectly pure and homogeneous condition should render the metal incapable of dis- placing hydrogen, but the reply was not yet to hand.The author would like to call Mr. Evans’ attention to the contribution in the present discussion from Mr. H. C. Lancaster, wherein an authenticated case was quoted of excessively pure zinc dissolving in acids actually at a far greater rate than zinc of ordinarily high purity. Whilst undoubtedly L‘ electrolytic ” that process could hardly be called “ electrochemical” in the sense in which the word was employed by Mr. Evans. Mr. Guild’s contribution on the optical side was particularly welcome, especially in view of the use that had been made in the present work of his method of measuring reflectivity. (The arrangement of apparatus used by the author was essentially that devised by Mr.Guild for use in another sphere of work.) Considering the curves obtained by plotting loss of reflectivity against time, the author was pleased that Mr. Guild had inter- ested himself in the distinctive shape of the curve given by copper (under conditions such that it passed through the characteristic sequence of colour changes). The attempt to show that the measured increase in reflectivity beyond a certain point represented an actual increase in the total light reflected was extremely interesting, while the observation that there must be a true increase in reflectivity for particular wave-lengths was certainly suggestive. The author was afraid, however, that the reasoning did not accord with the experimental evidence, in the absence of which Mr.Guild was clearly at a disadvantage. Throughout all the colour changes involved, both before the deep purple (which gave the minimum reflectivity) and subsequently, there was no evidence of discontinuity such as was necessary for Mr. Guild’s argument. The author felt bound therefore to agree with Dr. Rosenhain that the argument was L‘ unsafe,” although of very great interest. Mr. Guild’s remarks concerning flicker photometers were exceedingly attractive. In carrying out reflectivity measurements on tarnished (ie. coloured) surfaces, the desirability in principle of employing some form of flicker photometer had many times suggested itself to the author. He confessed however that the difficulties and apparent disadvantages (more especially in the direction of sensitivity) had deterred him from taking any steps.Even with the present method there had been difficulties to over- come before a series of readings (extending over a period of time) could be conducted upon the same specimen in such a way as to ensure that the differences observed were actually due to changes taking place at the metal surface. I n the absence of Mr. Guild’s assurance, these difficulties would appear to be greatly intensified with a system of flicker photometry. In spite of its shortcomings the present method appeared to fulfil the require- ments imposed upon it in a surprisingly satisfactory manner. Comparison with gravimetric results upon a series of specimens at a stage when com- parison was possible had yielded such good agreement, that the author had been reassured as to the soundness of the optical results at stages too early for the gravimetric method to be applicable.Nevertheless he entirely agreed as to the desirability on general grounds of settling the question as to what did actually happen to the total reflectivity of coloured specimens, and he trusted he might be in a position before long to follow up Mr. Guild’s valuable suggestion. Inst. Met., 9, 1923.DISCUSSION 929 With reference to Mr. Guild’s concluding remarks, the question of the ‘‘ terminal value ” involved an inherent difficulty in the reflectivity method, which obviously militated against comparison with the gravimetric method in the later stages; the author suggested, however, that the difficulty was unaffected by Mr.Guild’s proposals. In the first place, since in the present instance it was quite impossible to say what was meant by “complete corrosion,’’ it was equally impossible to assign any reflectivity value to this hypothetical condition. By taking, as the author had done, zero reflectivity as the terminal value, one evidently tended ultimately to get an asymptotic curve. But usually before asymptotic conditions were reached, mechanical difficulties intervened in the shape of the limited length of the optical bench. And before even that stage was reached the results tended to become more or less vitiated on account of the increase in the experimental error (due to the low intrinsic value of the reflectivity). Yet another cause of trouble might be mentioned in the irregularity sometimes exhibited at a compara- tively early stage by the specimen itself, more particularly in the case of zinc-copper alloys as mentioned in the text.It was a fortunate circumstance, however, that whilst it was in the very earliest stages that the method could be conducted with the greatest freedom from objection, it was just in those stages that the need for the method was chiefly felt. The author was grateful to Dr. Friend for his useful contribution. With regard to the point raised both by Dr. Friend and Dr. Rosenhain as to the chemical cleaning of the metal surface (meaning thereby the removal of the surface layer) he had to say that no such work had yet been done. He would point out that as a general method of preparation any form of chemical attack upon the metal had been deliberately avoided on account of the difficulty of getting rid of all trace of the reagent and the danger thereby of vitiating results.He agreed, however, that from the funda- mental point of view it would be of great interest to examine the behaviour of materials from which the surface layer had been removed chemically and he would take the suggestion to heart. The author’s interest in the enhanced similarity between the optical and gravimetric curves brought out by Dr. Friend’s method of plotting would no doubt go without saying, and he was glad that Dr. Friend had replotted the curves. The author appreciated the valuable part which the principle of the “ corrosion factor ” had played in the presentation of the results of Dr.Friend’s numerous researches; the thought of applying a similar prin- ciple to ‘( surrosion ” was a happy one, and the result obtained in the example chosen certainly appeared most significant. With regard to the absence (in the advance proofs) of a reference to the recent important work of Hinshelwood, this had resulted from hesita- tion as to whether it could be included relevantly (involving as it did both abnormal temperatures and abnormal atmospheres) with the several references given in the Introduction. For the purpose of the final copy, however, the author proposed to modify the context so that the omission could be rectified without conveying any wrong impression as to the pur- view of that most valuable paper. Touching the question of the application of Hinshelwood’s methods to the work of the present research, it appeared doubtful whether this could conveniently or advantageously be done, bearing in mind the special nature of the reaction investigated in Hinshel- wood’s work and the excessively greater rate of reaction over that which obtained at ordinary temperatures.Dr. Rosenhain had raised a number of interesting points, some of which had already received the author’s attention (vide szlpa). The obser- vations with regard to the tarnishing effects upon metal specimens stored930 ATMOSPHERIC CORROSION in desiccators were very opportune ; the author, however, could have wished that they had included a reference to the behaviour of iron, if only because this would have avoided the anti-climax of his supplementing Dr.Rosenhain on matters connected with metallographic work ! The author’s experience had been that whilst non-ferrous specimens (i.6. particularly copper and copper alloys) tarnished in the way Dr. Rosenhain had mentioned, iron specimens under the same conditions kept beautifully, permitting of their microstructure being examined, from the original etching, after a lapse of time running (to his personal knowledge) into several years. The reagents mentioned by the author on page 853 had been employed more for the purpose of removing grease than traces of moisture, but they certainly had the effect of minimising the irregularities of which Dr. Rosenhain had spoken. With regard to methods of measuring the amount of tarnishing, the author appreciated the value of Dr.Rosenhain’s remarks. The electrical resistance method would appear to have no very great advantage over the optical method, and was likely to be more troublesome in execution. The use of interferometer methods, with the view to measurement of the actual thickness of the films appeared, however, to be much more hopeful. The author’s interest in Dr. Rosenhain’s opinion of Tammann’s figures would no doubt be appreciated, but he could have wished that Dr. Rosen- hain had given at greater length his views on the general mechanism of tarnishing. Dr. Rosenhain’s final point had already been referred to in the reply to Dr. Friend. The distinction between roughness and the cold worked layer had been most usefully emphasised by Dr.Rosenhain. Hitherto apparently it was only the former factor which had received investigation in atmospheric corrosion work, either ferrous or non-ferrous. In this connection whilst roughness was known to be a most important factor in iron corrosion the author thought that the results of the c c field tests” in the present report had shown that this factor was of far less importance on the non-ferrous side. Dr. Simpson had given a most useful summary of the meteorological factors involved and it was a matter for satisfaction that this very important aspect of the problem had been represented by so eminent an authority. Whilst from the special nature of this contribution any further comment would be superfluous the author wished to assure Dr. Simpson that his statements were fully appreciated. Mr.Forsyth’s interesting communication was welcomed as representing an important and essentially practical view-point. With regard to the parabolic curves recorded in the report for copper and brass the author had come to the meeting prepared to say that these had been followed ex- perimentally for a period of approximately 700 days. Mr. Forsyth, how- ever, had gone better than that and had cited an example where, presumably, the parabola had persisted for 700 years! Exposed to rain, the amount of metal removed from copper and its alloys was of course quite appreciable although insignificant in comparison with that similarly removed from iron ; incidentally it might be of interest to mention that the author was utilising the chemical examination of the c c wash ” for the purpose of following the course of corrosion in non-ferrous specimens.As to the influence of this ‘‘ wash ” upon masonry it should be noted that the opinion of Mr. Forsyth as an architect was contrary to that of Dr. Fox as a chemist, a circumstance which might leave the layman more mystified than either. Personally the author preferred to take a neutral view, since while it was difficult to see in what way the metallic compounds carried by the rain water could haveDISCUSSION 931 any intrinsic preservative action, it was reasonable to suppose that rain water which had largely expended its corrosive contents in attacking the metal structure would be less active in its attack upon underlying masonry than rain water which had not been similarly neutralised.At the same time there could scarcely be two opinions as to the disfigurement brought about by the intrusion of metallic salts into the stone work, and it was interesting to note the preventative treatment which had been mentioned by Dr. Fox. With regard to the question about expansion of metals in relation to corrosion the author was afraid he had no specific information to give, although a remark of Dr. Simpson in the present discussion might be quoted with advantage : Besides the general effect of temperature, rapid changes must help to break up surfaces and tend to set up corrosive action.” I t was not difficult to understand how successive expansions and contrac- tions could help to break up an otherwise protective scale, and so accelerate the transition from “ surrosion ” to ‘‘ erosion.” The author hardly thought that Mr.Paterson wished to be taken too literally in his sweeping advocacy of laboratory methods of attack, which, by implication, would reduce to a vanishing quantity his opinion as to the value of any form of field test. In this connection, however, the author would like to refer Mr. Paterson to the remarks with which he had opened his reply to the discussion. He ventured, moreover, to emphasise his conviction that in the present kind of work field tests would always be necessary-and indeed that such tests should if possible precede the purely laboratory method of investigation. He might appropriately refer to an investigation on the tar- nishing of silver the results of which had only just come to hand.l Here vacuum methods had been adopted to some extent and the results obtained were of the greatest interest.Referring, however, to the comparison between the behaviour of fine and standard silver, the surfaces of which were pre- pared, presumably, by ordinary laboratory methods, a conclusion had been reached exactly the reverse of that recorded in the present report in connection with the “ kitchen atmosphere.” The author’s specimens had been polished in a works, and he may have been guilty of offending susceptibilities by exposing them in a kitchen, but he ventured to suggest that results such as those which had been obtained would have to be taken into consideration practically-however many laboratory experiments should prove them to be wrong! Turning to the constructive side of Mr. Paterson’s contribution the author placed extreme value upon this, and as soon as opportunity permitted he would certainly endeavour to follow up the suggestions con- tained therein.In connection with Dr. Fox’s communication, whilst this appeared to call for no specific reply, it contained so many detailed observations representa- tive of actual corrosion in the field and was accompanied by so much analytical data, that it constituted an invaluable addition to the literature, which certainly was very deficient in data of the kind that Dr. Fox had provided. The interesting results which Dr. Reynolds had quoted from his re- searches upon mercury appeared to the author to be extremely suggestive from the more general view-point of atmospheric corrosion.He offered no further comment at the moment, but was glad to have the data included in the discussion for the purpose of future reference. He felt fortunate moreover in the inclusion of the results of Dr. Reynold’s investigation on ‘‘ The Tarnishing and Detarnishing of Silver,” Vinal and Schramm, rournal of the Washington Academy of Sciences, 13 (rgq), 139.932 ATMOSPHERIC CORROSION the composition of the atmosphere since the important part likely to be played in corrosion phenomena by those “ incidental ” constituents needed no emphasis. The author had carried out some very limited experiments in order to determine the relative proportions of SO, and SO3 and had been somewhat surprised at the preponderance exhibited by the latter.He was consequently interested in Dr. Reynold’s remarks as to the rapidity with which SO, was oxidised in the presence of water and ozone. Dr. Reynolds’ observations as to ozone were of particular interest and seemed likely to appeal to a wider audience than that immediately concerned. The author was pleased to have Dr. Lessing’s contribution since he was alive to the advisability of keeping in touch with all possible phases of atmospheric corrosion, and had indeed collected a number of references relating to the problem which Dr. Lessing had described. That Dr. Lessing’s plaint should be necessary after such a large amount of research had been expended in this direction appeared to be significant, and might per- haps serve as warning to those who were unduly optimistic as to the rapidity with which ultimate objects could be achieved by a system of research.I t could not be doubted that surface tension effects were responsible for the anomalous behaviour of the silver specimens, but the difficulties in the way of isolation and investigation of those effects were only too evident. The author believed that it was not only possible but very probable (( that the ‘ fogging ’ effects are connected with grease, the more intimate contact for true tarnishing being prevented by it.” The (( fogging ” of metal surfaces (which was pointed out in the text to be intimately associated with those surfaces showing freedom from (( tarnish ”) would appear most probably to be governed by similar causes to those which brought about a like pheno- menon upon the surface of glass.In this latter connection it had been pointed out by W. B. Hardy 1 that ‘‘ the air consists for our purposes of elementary gases, water vapour, and impurities, and a surface of glass seems to condense these last to a greater extent than either the gases or water vapour. The film, when formed, is an exceedingly thin one; it has the general properties of an oil, and therefore Lord Rayleigh speaks of it as a film of ‘ grease.’ ” Referring to the slight differences in behaviour between dull-polished and bright-polished copper and brasses, the author certainly attributed the difference chiefly to the greater intrinsic surface possessed by the dull- polished specimens. With regard to the query raised at the end of Mr.Hall’s remarks one would naturally like to be in possession of further evidence before ventur- ing an opinion. Nevertheless it was somewhat difficult to see how the more rapid attack observed at the edges of the author’s freely suspended plates could be altogether comparable with the phenomenon described by Mr. Hall where one had the ‘( leaves ” stuck down on to a common surface. I t appeared more reasonable to look for the cause in the medium used for applying the leaf, in which connection its oxygen-carrying properties and its degree of acidity would suggest themselves. Each of these factors would be expected to operate mainly at the edges of each individual leaf to an extent dependent upon the properties of the particular medium used, and also, of course, upon the particular alloy used in the making of the leaf.The author had read the communication of Dr. B. S. Evans with the utmost interest. He regretted that in the pressure of experimental work he had overlooked the recent paper to which Dr. Evans referred. lie was The author appreciated Mr. Hall’s interesting contribution. y. SOC. Chem. Ind., 38 (rgrg), 7T.DISCUSSION 933 Per cent. Per cent. Per cent. therefore the more grateful for the present contribution, in view of the intimate bearing it had upon the author’s laboratory experiments. As mentioned in the report, the author had anticipated the possibility of SO2 acting in conjunction with some other constituent, but the extent to which he had been involved in other directions had prevented his getting very far with the experiments. He had actually done some little work with the addition of small amounts of HC1 to air and had found that (either under conditions of low relative humidity or of very thorough desiccation) these gave rise to the characteristic interference effects.I t was curious, however, that he had not yet tried HC1 in conjunction with SOz. Dr. Evans’ ob- servations therefore constituted a most opportune and valuable addition to the report. I t was certainly interesting that the effects produced had coincided with those observed in the “kitchen ” atmosphere, and not with those in the “basement.” The author would look forward with great interest to any further work which Dr. Evans might publish. The author appreciated the remarks which Mr.Bolton had made and the examples he had quoted from his own cognate work. With regard to the behaviour of iron he had to say that. no attempt had been made to investigate whether any relationship existed between the areas of initial attack and the microstructure of the sheet. With regard to Mr. Bolton’s inquiry as to the influence upon tarnishing of previous pickling or dipping treatments, this certainly came within the purview of the present investigation and the question was a pertinent one; the author regretted, however, that it had not yet been possible to carry out any work in that direction. The author was greatly obliged to Mr. Lancaster for his important contribution, which was to be welcomed as coming from a manufacturer interested in the scientific side. The instance given of metallic corrosion being developed for industrial purposes represented a somewhat unfamiliar view-point, yet one of much interest and significance. With regard to the influence of impurities in the author’s experiments with zinc, since this same question had been raised in the discussion by Dr. Bengough the author would refer Mr. Lancaster to the reply (albeit very largely negative) which he had given in that connection. He was now, however, in a position to state the analyses of the zincs used :-l Lead . . . . . . , 0.06 Iron . . . . . . I 0.025 Tin . . . . . 1 1 nil Copper . . . . nil A. High Grade (Re-distilled). 0.05 1.18 0’01 0’04 trace 0‘005 nil trace Cadmium . . . . . ~ 0’02 I 0.08 0‘08934 ATMOSPHERIC CORROSION The rate of dissolution of zinc in acids involved questions of funda- mental importance, in which connection the statement of Mr. Rigg was of extraordinary interest. So far as the author knew there was no other instance on record where zinc of such (ascertained) excessive purity had been employed in experiments of that kind. I t was significant to note that the results obtained were actually the converse of those frequently assumed to be associated with such conditions, and indeed postulated by one school of thouqht represented in the present discussion. I t was perhaps suggestive to recall that in the case of iron the presence of arsenic had been found greatly to retard the dissolution of the metal in acids. The view of Watts and Whipple that this effect was due to the high overpotential of hydrogen on arsenic would no doubt be generally accepted. In the light of Mr. Rigg’s statement it would thus appear reasonable to suppose that the value usually ascribed to the overpotential of hydrogen on zinc was a fictitious one due to the presence of impurity (possibly arsenic) whose influence had hitherto been overlooked. The fall in overpotential con- sequent upon the virtual removal of such impurity would thus readily account for the increased rate of solution of the metal in acids. With regard to the question which Mr. Lancaster had raised concerning the hammering of the plates, the author had to say that in all cases where the influence of physical condition had been under investigation, plates representative of the soft condition had been annealed subsequent to the hammering process. In view, however, of the very small order of the differences actually observed in materials representing maximum hardness and softness respectively (vide Brine11 hardness figures, p. 85g), it would appear very doubtful whether any appreciable influence could have been introduced (from the present point of view) by the hammering operation. The author was grateful to the President for the remarks with which he had brought the discussion to a close. He was interested to note that the opinion expressed by Professor Carpenter at the outset had elicited the support of Sir Robert Robertson. Touching the particular question of the chemical examination of tarnish films, however, the author thought he might reasonably ask for indulgence at the present stage. The circumstance that differentiation between sulphide and oxide had received some measure of attention in the present report might be taken as an earnest that the author was alive to its importance. Whilst further suggestive results had emerged since the writing of this report, it would no doubt be appreciated that these could be dealt with more conveniently in a subsequent communication. The author fully agreed that the chemical side should receive greater emphasis in the future, and he would further suggest that the opportunity to apply chemical methods would, from the very nature of the case, increase with increasing time. The author wished to express his thanks to all those who had contributed to the discussion, and who, by their constructive remarks had added so materially to any value which the present paper might be deemed to possess. In conclusion, the author desired to make appreciative acknowledgement to the Atmospheric Corrosion Research Committee, and to the Council of the British Non-Ferrous Metals Research Association, not only for their per- mission to publish the Report in its present form, but also for the actual facilities they had afforded to that end. Trans. Amev. Electrochem. SOL., -p (rg17), 257.

ISSN:0014-7672    

DOI:10.1039/TF9241900901

出版商:RSC    

年代:1924

数据来源: RSC

摘要:

REVIEWS OF BOOKS. Valence and the Structure of Atoms and Molecules. By GILBERT NEWTON LEWIS, Professor of Chemistry in the University of California. (American Chemical Society. Monograph Series. New York, I923 : The Chemical Catalogue Company, Inc. Pp. 172. Price 3 dollars.) Professor G. N. Lewis has in this monograph broken a silence that had already lasted for seven years, since he himself has made no important pro- nouncement on the subject of valency since the appearance of his epoch-making paper on “The Atom and the Molecule,” in 1916, although some of his colleagues, e.g. Latimer, Rodebush, and Eastman, have made some minor con- tributions to the development of Lewis’ theory. Professor Lewis has “devoted several of the earlier chapters to an attempt to bring to the better acquaintance of chemists some of the astounding accom- plishments of modem physics.” In this he has achieved remarkable success, since his account of the progressive development of the atomic theory, under the influence first of the periodic law and then of the study of spectral series, is brilliant in its simplicity, especially in the very difficult sections which depend on the application of the quantum theory to problems of atomic structure.In the section which follows Lewis deals somewhat fully with the magnetic properties of the elements, and uses the ring-electron of Parson as a bridge to bring together the static conceptions of the chemist and the dynamic models of the physicist. The reconciliation of these views has been made much easier since physicists have supplemented the classical laws of mechanics by the rigid limitations of the quantum theory.Thus the persistence of molecular structure (eg. in isomers, or in molecules which are undergoing substitution, etc.), is funda- mentalIy opposed to the extreme flexibility of any planetary system of the old- fashioned kind, but is much more concordant with the later view that an electron has to seek permission to move to a new orbit and that under normal conditions this permission is almost invariably refused ! In his sixth chapter Professor Lewis develops somewhat fully the theory of electron-sharing as the principal means of producing a bond between adjacent atoms. This theory is Lewis’ own, and is one of the main features which make his 1916 paper so much more valuble than the paper which Kossel published in the same year, and which is often spoken of as if it covered the same ground.Lewis lays great stress on the tendency of electrons to unite in pairs and quotes, as evidence of this, the electrical conductivity of fused iodine (which must there- fore contain even numbers of electrons in the ions I and I) of triphenylmethyi (C Ph3 and C Ph3) in sulphur dioxide, and of liquid nitrogen peroxide (which must therefore contain the ions NO, and NO,). He regards the loss of colour when NO, polymenses to NIOI as showing that the loose odd electron of NO, suddenly 935 + - - + - +936 REVIEWS OF BOOKS loses its freedom when it is paired with a similar electron and thus becomes rigidly clamped in the even-numbered electronic system of N,04.The chapter on the chemical bond is followed naturally by chapters on double and triple bonds and on co-ordination-compounds, and by a chapter de- voted to the peculiarities of elements such as boron which have such a small atomic number that the K as well as the L electrons appear to share in the development of valency. The book closes with a fascinating chapter on “The Discontinuity of Physico-Chemical Processes,’’ in which the two conceptions of numbering and measuring, the abstract theory of number, and the eminently practical science of geometry, are contrasted, and the inquiiy is made whether in the future only the former may be regarded as rigidly applicable to scientific problems. The con- tinuous fluid of hydrodynamics is clearly a fiction, and so is the ‘L fluid ” concep- tion of an electric current.Since these ideas have gone, is there any phenomenon that suggests a real continuum? Professor Lewis thinks that probably there is not, and that all the sciences which appear to depend on continuous properties will have to be re-organised on a statistical basis, as branches of the universal science of numbers. T. M. L. A Comprehensive Treatise on Inorganic and Theoretical Chemistry. By J. W. MELLOR, D.Sc. (London, 1923: Longmans, Green & Co. Vol. 111. : Cu, Ag, Au, Ca, Sr, Ba. Pp. 927. Vol. IV. : Ra and Ac Families, Be, Mg, Zn, Cd, Hg. Pp. 1049, Price 3 guineas net each volume.) The first two volumes of this notable work were reviewed in Vol. XVI I I . (p. 274) of the Transactions and its general character was there described. The present volumes have followed in a remarkably short space of time considering the magnitude of the work.It is very unsatisfactory when the early portions of a big work become out-of-date before the work is even completed. It may be appropriate to indicate here the general mode of treatment Dr. Mellor has adopted in dealing with the chemistry of the metallic elements. First the history, occurrence, preparation from its compounds and extraction of the metals are dealt with. Then follow accounts of its physical and chemical properties, with a section on atomic weight, crowded with numerical data. Finally, the principal compounds of the metals are dealt with, far more attention being paid to their physical properties than is usual in books on chemistry.The unimportant or more complex compounds, when not of special interest, are referred to incidentally and briefly. The treatment throughout is predominantly physico-chemical. The vast field covered has necessitated many sections being little more than catalogues of numerical data and we are tempted to think that perhaps the author has overstrained his desire for completeness. Many facts of historical interest only might have been dispensed with, but on the other hand all such facts are very fully referenced and this will render the book a most con- venient starting-point for detailed investigation of the history of any particular product, process, or hypothesis. The lists of references at the end of each section are bewildering in their range and completeness, Volume 111.deals with Copper, Gold and Silver, and with the alkaline earths Calcium, Strontium, and Barium. No useful purpose would be served in criticis- ing this arrangement from the standpoint of the periodic classification ; probably That is as it should be.REVIEWS OF BOOKS 93 7 the author was guided by reasons of practical convenience. Unlike in Volumes I. and 11. the present gives few opportunities for excursus on matters of general chemical interest. One such opportunity is, of course, afforded in the chapter on Silver, and here Dr. Mellor introduces an admirable summary of photo- graphic theory which is as up-tc-date as possible. It is interesting to note that the author-who generally endeavours to observe an objective standpoint in matters of theory-favours the solid solution theory of the latent image.The paragraph on sensitisers is not very good and the word is not to be found in the index. The subject of the properties of colloidal solutions is appropriately introduced in the chapter on Gold. Volume IV. deals with the Radium and Actinium metals, and with Beryllium, Magnesium, Zinc and Cadmium, and Mercury. Here again the arrangement is open to criticism from the strict systematic point of view. Consideration of radio- activity gives the author an opportunity to introduce important chapters on ‘( The Structure of Matter,” and ‘( The Architecture of the Atom.” The treat- ment of the subject in the former is properly based on spectrum analysis and the phenomena of electric discharge.Description of the photo-electric effect is followed by an excellent summary of the radiation theory of chemical action, which appears to be based on the Faraday Society’s general discussion, although there is no reference to the report of that discussion. A curious and characteristic section on alchemy forms a link between the treatment of radioactivity and atomic structure. The latter subject, so difficult to condense satisfactorily, is on the whole well developed, although rather unbalanced in parts, but the field is adequately covered. The simple derivation of the Bohr orbits, given on pp. 167 and 168, will be found extremely useful by readers who want the essence of the matter without its mathematical difficulties. It is really astonish- ing how the author has managed to incorporate the most recent work available when the separate volumes were printed.Thus, in the chapter on Mercury we find reference to the most recent experimental work on the separation of the isotopes of that element. A curious omission-unless the fault is that of the reviewer-is that the cyanides are not dealt with. Are these regarded as organic compounds? The cyanides of many metals are of some importance in the arts and the omission is regrettable. We wish the author had not adopted the practice of adding the initials to proper names. It may be defended in the case of living workers of minor rank, but it is surely a little absurd to give initials to immortals like Newton, Laplace or Faraday. It is the very magnitude of this remarkable treatise which perhaps tempts one to criticise it in unimportant details. We cannot refrain from ending once again on a note of wonder, how one man could have collected together and presented in so attractive a fashion such a vast quantity of material and of admiration for his learning, skill, and industry. Theoretical Chemistry from the Standpolnt of Avogadro’s Rule and Thermodynamics. By Professor WALTER NERNST, Ph.D.Fifth English Edition revised in accordance with the Eighth-Tenth German Edition by L. W. CODD, M.A. (London, 1923: Macmillan & Co., Ltd. Pp. 922. Price 28s.) Few books have done more to spread the modern doctrines of physical chemistry than Nernst’s famous treatise, and although a whole library of works938 REVIEWS OF BOOKS on this aspect of chemistry has been written since the first Nernst was published in 1893, the book still, in many respects, stands in a class apart.We, therefore, heartily welcome the appearance, after an interval of eight years, of a new English edition. Professor Nernst has his own conception of what constitutes physical chemistry, and his book is an elaboration of that conception. To him physical chemistry is not a new science, it is the uniting of two sciences hitherto somewhat independent of each other. If that was true thirty years ago its truth is more than ever evident now, when so much advance in chemistry is being made by physicists and when so much chemical knowledge is being utilised in laying afresh the foundations of physical knowledge. Consistent with his principle the author has, therefore, included in his book all that the chemist must know of physics and all that the physicist must know of chemistry.The general plan and contents of the book are so well known to every student of physical chemistry that we need only comment upon the special features of the edition before us. In Book I. “The General Properties of Matter,” few additions have been made, although we notice that the translator has introduced several references to important work (for example, that of Berkeley and Hartley on semi-permeable membranes) not noticed in the text. Book 11. is on “Atom and Molecule,” and here the results of modern experi- mental work and theory are naturally drawn upon. The essential difference between the classic and quantum method of treating atomic problems is de- veloped with commendable clearness and simplicity (pp. 199 and 272 ff.and again on p. 512) and the application of the quantum idea to the molecular theory of the solid state, a subject which the author has made his own, deserves special mention. Brief reference only is made to modern developments in X-ray spectroscopy. The German edition on which this translation is based was written in 1920, and there is, consequently, no attempt to utilise electronic theory to clear up some of the difficulties referred to in the older theory of valency. For the same reason the latest work on isotopes is not referred to, although the brief chapter on radioactivity has been largely rewritten. The chapter on colloidal solutions is disappointing in a book designed to give special attention to the states of matter.In Book 111.-“The Transformation of Matter”-few important changes have been made. The author accepts, with some reserva- tion, the dissociation theory of strong electrolytes put forward by Ghosh, although this has since been subject to some severe criticism. In Book IV.--“The Transformations of Energy ”-reference is made to the observations of Smits on retardation phenomena in the determination of transition points, but the author is not prepared, as yet, to found thereon a general theory of allotropy. In the chapter on electrochemistry the author maintains his older views on the origin of electromotive force in a galvanic cell ; he does not refer directly to the sup- port given to the old contact theory by modern electronic conceptions of the photo-electric effect.Nernst’s ‘‘ Theoretical Chemistry,” incomplete though it be in some respects, will always possess an interest and importance of its own. Students of physical chemistry may find other text-books more useful for examination purposes, but they cannot afford to neglect Nernst if they wish for a philosophical understanding of their science, for here they will follow its development, from his own particular standpoint, at the hands of a master, one of its creators. F. S . S .REVIEWS OF BOOKS 939 The Chemical Elements. By F, H. LORING. (London, 1923: Methuen & Co. Ltd. Pp. 172 with 14 tables and 4 diagrams. Price 8s. 6d). Mr. Loring has published during the past 14 years a series of papers, mainly speculative in character, in the Chemical New, and has already written a book on Atomic Theories. The present volume is largely based upon his articles in the ChemicaC News. It has probably been compiled on account of the current demand for books dealing with the fundamental problems of atomic and molecular structure ; but the author is not a specially skilled ex- positor, and has not himself contributed substantially to the amazing progress which this subject has made in recent years. The serious student would therefore be well advised to derive his information from original sources, or at least from an author who can handIe the documents with the authority that can only be acquired by direct contact with experimental work Moreover, in view of the fact that attractive monographs have recently been written by Lewis, Aston and Bohr, there is no argument which would justify him in reading books which are obviously of a lower order of merit.The Properties of Matter. BY B. C. MCEWAN. (London, 1923 : Longmans, Green & Co. Pp. 316. Price 10s. 6d.) The volume before us deals, in a very competent manner, and with a wealth of experimental illustration, with the subject viewed from an angle which is not quite the customary one. Exactly one half of the book is occupied with a discussion of the first Law of Thermodynamics, the Kinetic Theory of Matter, Isothermal and Adiabatic Transformations and the Specific Heats of Gases, Elasticity of Gases and the Continuity of the Liquid and Gaseous States, Thermal Expansion Diffusion and Solubility of Gases, and Equations of State.It is clear that many of the doctrines here expounded are usually relegated to a treatise on Heat, and their inclusion in a volume bearing the title of Properties of Matter is to be decided as well by considerations of expediency as by the taste of the author. Admirably as they are treated here, it seems to the reviewer preferable to preserve the traditional classification, for the space allotted to these topics necessitates the discussion, in some hundred and fifty pages, of such important subjects as the general properties of liquids, capillarity, elasticity torsion and flexure, and the determination of the constant of gravitation, and of the acceleration due to gravity. This leads inevitably to a huddled mode of presentation which is agreeably absent from the first part of the work.Much water has flowed under the bridges since the days when the treatises of Tait and of Poynting and Thomson first saw the light, and it is with some surprise that one notes, in the section dealing with compressibility, no reference to the very important work of Bridgman. As usual, the distinction between free and total surface energy is not clearly brought out, and the conditions under which it is legitimate to apply the simple formulz for the depth of a sessile drop are wrongly quoted. Considerations of space presumably have led to the omission of the simple but beautiful argument of Boys concerning the relation between the sensitiveness and dimensions of a torsion balance.And it is surprising to find, in a volume published under the date 1923, no more than a passing allusion to the Brownian movement. These lacunae notwithstanding, the book is well suited to the needs of pass and junior honours students reading for a science degree. A. F.940 REVIEWS OF BOOKS Theoretical and Applied Colloid Chemistry. By Professor WOLFGANG Second and Enlarged American Edition translated from the (London, 1922 : OSTWALD. Eighth German Edition by Dr. MARTIN H. FISCHER. Chapman & Hall, Ltd. Pp. 266. Price 12s 6d. net.) This book is described on the title-page as an introduction to the world of neglected dimensions. It is not intended to be a text-book but a stimulus to the study of colloidal phenomena, addressed to the general scientific reader.It is based on a series of lectures delivered in 1913 and 1914 at various universities and colleges in America given with the object of drawing attention to the im- portance of colloid chemistry, its great possibilities of scientific and technological application and the fascinating interest attaching to its study. In Dr. Ostwald’s own words the volume is a ‘( propaganda sheet for colloid chemistry.’’ It is divided into five lectures. The first deals with the fundamental properties of the colloidal state and methods of preparing colloidal solutions ; the second with the classification of colloids and their ph ysico-chemical properties ; the third with their changes in state ; and the last two with some scientific and technical applications of colloid chemistry. In the last chapter we observe the very necessary reminder that although conscious application of colloid chemistry to technology has not as yet been made in anything like the degree possible or probable, yet colloids constitute the most universal and the commonest of all things we know.The author further insists, that in industries based on materials of a colloid nature the details of technical procedure need to be rewritten in terms of colloid chemistry. The unrivalled knowledge of the subject possessed by Dr. Ostwald is sufficient guarantee of the range and accuracy of his treatment, while its attractive and pointed style is a reflection of his enthusiasm for this branch of science, so peculiarly his own, and of his faith in its unlimited possibilities. We have sufficiently indicated the purpose of the book.Clouds and Smokes. By WILLIAM E. GIBBS, I).Sc. Churchill. Pp. xiii + 240. Price 10s. 6d. net). (London, 1924 : J. & A. The sub-title of this work : ‘‘ The properties of disperse systems in gases and their practical applications ” indicates the point of view from which the author has arranged and presented a vast amount of scattered and-in part- inaccessible material. After a short introduction on heterogeneous systems and the effect of curvature of the interface, the formation of aerosols (a convenient title introduced by Svedberg) by dispersion and by condensation processes is discussed and their various physical properties are described. A good account of the Brownian movement and of the optical and thermal properties, as well as of the electrical behaviour is given, and even such familiar phenomena as the deposition of dust in interiors heated by different methods are mentioned and explained.The chapter on the stability of aerosols contains a great deal not to be found in existing text-books, and includes some very interesting photo- graphs of a (‘ coagulating ” zinc oxide smoke. The second part of the book is devoted to “The industrial treatment of fumes and dusty gases.” The principal methods used for removing disperse matter from gases, such as settling, centrifuging, washing and electrostatic separation, are briefly described and illustrated. Although a good deal has been published regarding the last named process, the scale on which it is used may surprise some readers.REVIEWS OF BOOKS 941 The book fills a distinct gap in the literature of disperse systems and its value is enhanced by a very full bibliography.Printing and illustrations are very good, and proof reading seems to have been done with care, though it has failed to detect a particularly unfortunate error both on p. I and on p. 41, where the average velocity of a gas molecule is given as being of the order of IO-‘ ” instead of 104 cm. The reviewer knows the difficulty of persuading compositors that both positive and negative exponents have their raison &&re, but has generally found that it could be overcome by firmness in demanding revises. E. H. Light and Colour. By R. A. HOUSTON, M.A., Ph.D., D.Sc. (London, 1923 : Longmans, Green 81 Co.Pp. 179. Price 7s. 6d.) While intended chiefly for amateurs and, more particularly, that large and often very intelligent section of the public interested in photography, colour printing and so forth, this interesting book contains much that the student of physics will like to have in a simple, readable form. The popularity of the treatment is in this instance by no means synonymous with looseness of expres- sion or vagueness of argument. The first few chapters deal with the nature of light and radiation, and colour. A section on X-ray spectrometry leads to a brief account of atomic structure and stellar magnitude. The treatment of colour is very clear and should prove helpful to many people who have been confused by much loose writing on this subject ; it is based on the colour triangle method of exhibiting the relations of primary and derived colours.I)r. Houston holds an even balance between the classical three-colour theory of vision and the non- elemental theory associated with the name of Edridge-Green, and his words deserve to be quoted seeing that the controversy still rages : ‘‘ . . . the mathe- matical development of Helmholtz’s modified theory does equally well for the non-elementary theory, so that there is no serious difference between the two standpoints.” The account given of colour photography is commendedly simple, brief though it be. There are chapters on The Light of the Future, Photo- chemistry (in which a photoelectric explanation of the photographic process is indicated) and Phototherapy. The last chapter describes some of the remark- able, little-known and, at present, inexplicable phenomena, summarised under the name of The Psychology of Colour, but we think the subject is more far reaching than the author‘s treatment indicates.It is doubtful whether the theory -apart from the facts-can be adequately discussed without reference to the whole big subject of aesthetics. A very useful and interesting book, which can be strongly recommended. The Metallurgy of Steel. By F. W. HARBORD, A.R.S.M., F.I.C. and J. W. (London, 1923 : C. Griffin & Co., 32s. net each volume.) HALL, A.M.1nst.C. Eng. Ltd. Vol. I. xii + 545 pp. Vol. 11. xv+ 553 pp. 7th edition. ‘‘ Harbord and Hall,” ever since the appearance of the first edition in 1904, has been looked upon as the standard work in the English language on the metallurgy of steel.The treatment of the subject is intended to be exhaustive in character and with succeeding editions it has grown from a single volume of about 750 pages till in the present edition it consists of two bulky volumes (totalling some I 100 pages) which for convenience are being sold separately. In the preface to this new edition, it is stated that the volumes have been942 REVIEWS OF BOOKS thoroughly revised, and hence one looks with considerable interest to see how this revision has been carried out. Dealing first with Volume I., which is devoted to the purely metallurgical side, one is bound to experience a considerable amount of disappointment at the unsatisfactory nature of the revision. From a survey of the whole of this volume it would appear that, with the possible exception of the chapter on Electric Furnaces, the revision has taken the form of interpolating short para- graphs giving references to recent work or improvements.Owing to this, the plan of the work remains largely as it was in the first edition published twenty years ago. In the descriptions of the Open Hearth and Bessemer steelmaking processes and furnaces, the effect of this may be fairly satisfactory though it leads to somewhat of a patchwork effect. In these chapters however, one is struck with several notable omissions. Thus in those devoted to the open hearth furnace, descriptions are given of new types of ports and other details of construction, but apparently no reference is made to Clements’ work on British Siemens Furnace Practice.Again, in view of the fundamental importance of casting conditions on the properties of the steel and the impossibility of removing by any subsequent process, short of remelting, some of the characteristics im- pressed in the metal at this stage, it would have been expected that an adequate account would have been given of the mechanism of solidification and of the influence of the shape of mould on the extent and position of the pipe, with some reference to the important work of Brearley and others on this subject. On the contrary, the influence of mould design on the pipe is dismissed in a few h e s , and the only reference to Brearley’s work which the reviewer has been able to discover occurs in Volume 11.devoted to the Mechanical Treatment of Steel ! When one considers, however, the part of Volume I. dealing with the metallography, constitution, and heat treatment of steel and the properties and uses of alloy steels, the effect of the unsatisfactory nature of the revision becomes very obvious. These subjects have been developed to a relatively enormous extent during the past two decades. In the period just preceding the publica- tion of the first edition, the subject of the constitution of steel was the battle- ground of several opposing theories ; the basic principles underlying the heat treatment of steel were not thoroughly appreciated or even understood, and the knowledge of alloy steels was to a considerable extent confused, largely as a result of the fact that the necessity for their correct heat treatment was not realised.This state of affairs has changed considerably during the last twenty years ; thus heat treatment has acquired to a great extent a scientific basis, while careful experimental work has taught us much concerning the constitution of steel and the properties of alloy steels. On turning to the chapters in Volume I. dealing with these subjects, one finds that in dealing with Heat Treatment, for example, a great deal of space is taken up with accounts of investigations which were carried out before the principles underlying the subject were understood. While such investigations are of interest to a student who wishes to trace the gradual development of the science of steel metallurgy, they are of doubtful value to the engineer who wishes to know how steel should be treated and why ; incidentally if he knows anything about the subject at all he will recognise that some of the conclusions then reached are quite opposed to fact, and yet these conclusions are still printed in full without any comment I In the same way, in the metallographical portions, there are detailed accounts given of how several pioneers in the subject prepared theirREVIEWS OF BOOKS 943 microsections at a time when the commercial production of polishing materials had not commenced, while on the other hand such matters, surely of greater importance, as sulphur prints, Humphrey’s method of macroetching and contact printing and Howe’s acid etching to develop the macrostructure are apparently ignored. Again there are several pages given to expositions of the older theories on the constitution of steel, theories now either abandoned or very con- siderably modified, while the more recent developments, as for example X-ray investigations and the effect of such on the theoretical side, are practically ignored. With regard to alloy steels, the busy engineer who is interested in such steels for motor or zero purposes will find pages of matter dealing with early investigations, much of which is only of slight interest to him, but he will not find much information to guide him in the selection of different steels for specific purposes ; such informatior as, for example, would help him to decide whether under given conditions a 3 per cent.nickel steel or a similar steel containing in addition about I per cent.of chromium is the more suitable, or whether he should choose a chrome-vanadium steel in preference to either. ‘‘ Harbord and Hall ” has been such an institution in British ferrous metallurgy that one expects the very best from it, and is therefore the more critical of any shortcomings it may possess. In order that it may retain its premier position, the first volume requires thorough revision in the sense that a number of the chapters should be completely redrafted and rewritten in the light of modern experience and not merely patched up. In this respect the present revision of Volume II., dealing with the Mechanical Treatment of Steel is much more satisfactory than that of its companion volume. A considerable amount of new matter has been incorporated and much of the old redrafted or rewritten.In addition an interesting chapter has been added dealing with the origin and progress of steel manufacture in the principal steelmaking countries together with some ideas as to what is likely to occur in the immediate future. J. H. G. M. Materials and their Application to Engineering Design. By E. A. ALLCUT M.Sc. (Eng.), and E. MILLER. (London, 1924 : C. Griffin & Co., Ltd. Pp. xiii + 519. In the present volume, the authors have endeavoured to deal in a practical manner, for the benefit of the busy engineer who cannot spare time to consult metallurgical papers or treatises, with the variety of metals-both ferrous and non-ferrous-available for engineering use, with their chemical composition and constitution, with the effect on the latter of varying casting conditions, mechanical work and heat-treatment, with the effect of such variations on their mechanical properties and also with the methods used in measuring these properties. A general perusal of the book suggests that the authors have been very successful in their efforts.Their treatment of the subject is clear and logical and there is no doubt that it will be a useful and valuable book to many engineers. A number of minor criticisms could be levelled at some of the details given, for example, some of the temperatures recommended for the heat-treatment of certain grades of steel would not be regarded as the best possible by many steel metallurgists while the authors are likely to confuse the non-metallurgical reader by suggesting that the normal change from austenite to pearlite at the Arl point in steel takes place via martensite, troostite, and sorbite-an idea quite opposed to fact.As a whole, however, such faults as the book exhibits are of a minor character and do not detract to any great extent from its general good qualities. 32s. net.)944 REVIEWS OF BOOKS The Micro-organisms of the Soil. (London, 1923 : Longmans, Green & Co. 17 tables. Price 7s. 6d.) By Sir JOHN RUSSELL, F.R.S., and others. Pp. 188 with 24 diagrams and The subject matter of this work is based on a series of lectures delivered in the Botanical Department at University College, London, and is indeed in the nature of a series of essays characterised by diversity of treatment rather than continuity of narrative : a feature which has the virtues of its defects.As one in the series of Rothamsted Agricultural Monographs the text con- cerns itself chiefly with the investigations there carried out, the work on soil biology elsewhere being for the most part dealt with only in so far as is necessary to a proper appreciation of the Rothamsted results. In the first chapter Sir John Russell gives a brief summary of the develop- ment of the concept of a soil population which concludes with an approximate estimate of the different groups as represented at Kothamsted. From this it would appear that, of the total organic matter in the soil, the soil organisms account for about one quarter per cent., although of this only about a third part is to be attributed to the microscopic flora and fauna.As Sir John justly remarks such numerical data give no idea of the relative importance of the various groups, which depends on their respective demands on the energy supply of the soil and the character and magnitude of the physical and chemical changes they effect. The physico-chemical changes constitute, however, just that aspect concern- ing which least is known but to the elucidation of which Rotharnsted is contribut- ing in no small degree. Mr. Thornton in two admirable chapters on the soil bacteria emphasises this importdnt aspect. Beginning with the dead remains of autotrophic organisms the carbohydrates and nitrogenous compounds respectively form the starting-point of a series of exothermic reactions, mostly oxidations, by which a whole sequence of bacteria derive their energy and a variety of chemical substances are produced.The amount of energy liberated may be small, as in the oxidation of nitrite to nitrate, or large, as in the oxidation of methane to water and carbondioxide.. Not, however, until our knowledge is much more extensive can we hope to estimate the relative importance of the different species as energy transformers. On the more chemical side the problems are sufficiently complex since there must be maintained a delicate balance in a chain of reactions due to different organisms of which the optimal activity is dependent upon conversion of the pro- ducts of their metabolism. Thus the efficiency of azotobacter is dependent on the presence of adequate bases in the soil and, as shown by Mr.Cutler in the chapter on soil protozoa, the frequency of this organism in common with other bacteria is dependent on the infrequency of protozoa. This inter-relation is further illustrated by the increased nitrogen fixation which bacteria exhibit in the presence of soil algae which form the subject of a chapter by Dr. Bristol. Increased acidity of the soil apparently has a depressing influence, alike on bacteria and protozoa, but Dr. Brierly, dealing with the soil fungi, quotes data showing that an increase in acidity of the plating medium from pH5 to pH4-3-4 resulted in the development of nearly double the number of colonies. The general effect of habitat factors is again emphasised by Dr.Imms, who summarises the nature and distribution of the invertebrate soil fauna of manured and unmanured plots at Rothamsted. Both plots show the usual vertical gradient which is so marked a feature of undisturbed soils, in this and otherREVIEWS OF BOOKS 945 respects, but the number of invertebrates in nearly all groups is considerably higher in the manured ground. In the concluding chapter Sir John gives a suggestive outline of the physico- chemical equilibrium of the soil which stresses the need for invest:gations on the r6le of particular organisms and in general their importance in determining soil fertility. When one recalls the disastrous results that have often attended interference by man with the balance of nature amongst the higher organisms, it is scarcely to be wondered at that progress in the control of the soil population is as yet in its infancy.The wonder, when we recall the delicacy and complexity of the balance, merely adumbrated in these pages, is not that we can do so little but that we can do so much, and it is probably no exaggeration to state that this is mainly the outcome of a happy combination of the methods of pure science and technological research. The student who has perused these chapters will find that the (‘ idea of the soil population ’’ has taken definite shape, and it is no small tribute to the various contributors that the impression which they leave is more of the vast field that awaits exploration than of that small part already surveyed. We may add that there are short bibliographies appended to the different sections, that the printing is clear and that the misprints are few.We would, however, express the hope that in future volumes of the series a combined author and subject index will replace the separate indices. The latter practice can only be justified where the number of citations of each class is exceptionally large. E. J. S. Lead : its occurrence in nature, the modes of its extraction, its properties and By J. A. SMYTHE, M0i:ographs on Industrial Chemistry, Edited by Sir EDWARD (London, 1923 : Longmans, Green & Co. uses, with some account of its principal compounds. Ph.D., D.Sc. THORPE, C.B., LL.D., F.R.S. Pp. 343. Price 16s. net.) Dr. Smythe has done a real service in collecting the essential facts regarding the chemistry, metallurgy and technology of lead, and presenting them in a form much more readable than is usually found in books of this kind.Although the treatment of the subject is exceedingly thorough, the author has avoided the common mistake of burying the really valuable truths beneath a dust of worthless details. The book opens with a brief history of the metal, followed by a chapter devoted to the principal ores. It is the third chapter which will most interest the physical ‘chemist. Here the existing knowledge of the chemistry of roasting and smelting is brought together in a compact manner. Although, as the author points out in the preface, our knowledge is far from complete, yet the satisfactory presentation of the information now available is the first step towards the investigation of the points which are still uncertain.Particulars of the equilibrium conditions of the various reversible reactions involved are given, so far as they are known, and the mechanism of the roasting and smelting processes is discussed in a sensible fashion. For instance, in considering the function of lime in lime-roasting, the reader is not encouraged to accept the somewhat fanciful view that calcium plumbate-or perhaps calcium peroxide-acts as an intermediary in the passage of oxygen to the galena. The more probable VOL. XIX-T34946 REVIEWS OF BOOKS explanation suggested is that the lime serves to absorb sulphur dioxide, the pro- duct of the reaction, as well as to prevent the charge from clotting. The description of the metallurgical processes, as well as that of the manufacture of the compounds, is very clear, and is illustrated by good diagrams.Although obsolescent methods are mentioned, more modern processes receive full attention. Numerous tables, showing the composition of the various products at different stages, add to the value of the work as a book of reference, whilst there are numerous references to scientific literature, including recent papers. The only serious omission in the book is the absence of any description of the intricate methods of concentration which serve to separate the lead- minerals of the ores from the accompanying zinc-minerals and gangue. These concentration processes have undergone much more rapid changes during recent years than the smelting proper, and in a new book on lead it is a descrip- tion of the earlier treatment of the ore that is likely to be looked for most eagerly.Perhaps, however, the absence of such a description from the present volume may indicate that Dr. Smythe has in view a separate work on this subject, which would be greatly welcomed. U. R. E. The Genesis of Petroleum. By P. E. SPIELMANN. (London : Ernest Benn, Ltd., 1923. Pp. 72. 5s.) The steadily growing economic importance of petroleum has aroused an increasing interest in the speculations and theories formulated to explain its probable origin and mode of formation. Dr. Spielmann presents in this little volume a summary of Ithe literature published on the subject during the last decade. His critical examination of the material leads him to conclude that there is overwhelming, though not completely unquestioned evidence in favour of the organic and against the inorganic origin of petroleum.He discusses the question of a sufficiency of vegetable and animal matter having been available to account for the existing oil deposits, laying stress on the differences of raw material and conditions of chemical and physical changes, both in sitzr and during migration by which the final composition of the oil, as found in any particular field, is determined. The summary will be found useful by every student of this important subject. R. L. Biomathematics, being the Principles of Mathematics for Students of Biological By W. M. FELDMAN, M.D , B.S., F.R.S.E., with an Introduction (London, 1923 : Charles Griffin & Science.by Sir WILLIAM M. BAYLISS, F.R.S. Co., Ltd. Pp. 398. Price 21s. net.) We have long had text-books in mathematics written specially for physicists, engineers and chemists, but in this book a course of mathematics has for the first time been designed to meet the special needs of biologists and medical men. Both the author and the publishers are to be warmly commended for their enterprise in producing so novel a work. Purists may say that mathematics should be studied as such, without regard to the particular use to which it is to be put. The argument may have some force when addressed to physicists and engineers, for mathematics is the very foundation of their sciences. It is, how- ever, quite irrelevant as applied to the biological sciences, which are only now beginning to emerge from the (6 descriptive ” stage and to become ‘‘ exact,” forREVIEWS OF BOOKS 947 in these days of extreme specialisation it is essential so to shap the mathematical weapon that it may be used by the student of biology with the minimum of effort.Although the book covers almost the whole range of applied mathematics, Dr. Feldman has very wisely begun at the beginning, assuming in his reader only the simplest school-knowledge of arithmetic and algebra. The biological examples adduced under such headings as Simplified Methods in Arithmetic and A Few Points in Algebra and Elementary Trigonometry convince one of the soundness of his method, which may be illustrated by reference to some of his ingenious applications. For example, the use of simple trigonometry is illustrated by calculations on the work performed by muscles ; mensuration by examples dealing with the numbers and surfaces of air cells and bacteria and the mechanism of the tubules of the kidneys ; the compound interest law by the rate of cicatrisation of a wound, the hydrolysis of cane sugar and so forth.The chapter on Functions includes a clearer account of nomography than one usually finds in books on applied mathematics. Some striking biological applications in the chapter on Maxima and Minima are calculations on the growth of infants, the ionisation of protein and the form of blood vessels. The biologist must be something of a physical chemist nowadays ; he cannot understand reaction so important to him as the dissociation of oxyhoemoglobin without a general knowledge of the law of mass action and for that simple calculus is indispensable (In his Introduction Sir William Bayliss points out that the data on which this dissociation formula is based can also be fitted by an adsorption formula.) The last and longest, and in many respects the most complete, chapter in the book is that on Biometrics, or the application of statistical methods to the measurements of variable biological quantities.We have described the book sufficiently to indicate its scope and usefulness. It needs to be added that the exposition throughout is clear and concise and the careful choice of type has made it easy to read. It is a book that no modern student of biology or medicine can afford to ignore, if he wishes to be able to follow the best work of his day. It may here be recalled that the most eminent of our younger physiologists was trained as a mathematician and a physicist. Notes on the Composition of Scientlflc Papers. By the Rt. Hon. Sir T. CLIFFORD ALLBUTT, P.C., K.C.B., M.A., M.D., F.R.S., etc. (Third Edition, London, 1923. Pp. 192. Price 6s.) This is a book which the harassed editor of learned Tramactions would like to be able to present to every author before his paper, having been accepted by a publication committee, has to be put into a form fit for printing. It is gratifying to note that the book has passed into its third edition since it first appeared in 1904, but loose writing and crude, involved modes of expression are still painfully common in scientific papers and, speaking with some personal feeling, we sincerely hope that this book will eventually reach the hands of every worker in science whose ideas or results are intrinsically worthy of publi- cation. Although the author addresses himself primarily to writers of medical papers his advice is of quite general application ; indeed it is not the scientific writer only who can profit by his ripe experience and sage counsel. Lucidity, simplicity, precision, force, are far more fundamental than, although they are inextricably connected with, what is usually understood by ‘‘ style ” ; but whereas style can be attained only by the girted few, these fundamental qualities can be948 REVIEWS OF BOOKS acquired by everybody who has thoughts or knowledge worthy of translating into words. The book is divided into two chapters ; the first dealing with some general principles to be observed in planning and writing a scientific paper, and the second with some detailed rules of word-choosing and sentence-building (that is ‘‘ coinposition ”), the neglect of which tends to obscure and ugly writing. For the rest the reader is advised to ‘‘ converse with great authors, in poetry as well as prose ’’ ; no sounder advice could be given.

ISSN:0014-7672    

DOI:10.1039/TF9241900935

出版商:RSC    

年代:1924

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 948 REVIEWS OF BOOKS BOOKS RECEIVED. Fifth Report on Colloid Chemistry and its Oeneral and Industrial Ap= plications. (London, I923 : H.M. Stationery Office. Pp. 130. Price 2s. 6d.) This is the fifth Keport of the Committee of the British Association on colloid chemistry, of which Professor F.G. Donnan is Chairman and Dr. W, Clayton, Secre- tary. In addition to the following papers the Report contains an Index to the whole series of five Reports, as it is not proposed to issue any more. Contents.-The Measurement of Surface Tensions. By Allan Ferguson. Report on Collagen and Gelatin. By Professor H. R, Proctor, D.Sc., and John Arthur Wilson. Industrial Applications of Wetting Power. By W. H. Nuttall. Colloids in Relation to the Manufacture of Inks. The Manufacture of Artificial Silk in Relation to Colloid Chemistry. By Edward Wheeler. Refractories for Electric Furnaces. Published by the American Electro- chemical Society, Columbia University, New York City. (Pp. 94. Price to members of the Faraday Society, one dollar.) This Report is based on the proceedings of one of the meetings of the Electric Furnace Association of America, but fresh material has been added, CoittEnts.-Refractories for Electric Furnaces.By Raymond M. Howe. Refrac- tories for Electric Furnaces. By Clyde E. Williams. Some Properties of Refrac- tories. By R. T. Stull. Refractories for Electric Furnaces. By Homer F. Staley. Electric Furnace Refractories. By C. W. Berry. Aluminous Refractories for Electric Furnaces. By L. C . Hewitt. Electric Furnace Refractories. By A. F. Greaves- Walker. Carborundum Refractories in Electric Furnaces. By M. L. Hardmann. Re- fractories for Electric Furnaces. By Refractories Dept., Norton Co., Worcester, Mass. Discussion. Index. Chemical Synonyms and Trade Names.By WILLIAM GARDNER (London, This Dictionary which, we believe, is the only book of its kind, gives the chemical names corresponding to the synonyms and trade names (and vice versa) of chemical materials commonly employed in manufacture and pharmacy. The book contains 14,000 definitions and cross references and the entries include minerals, dyestuffs, ex- plosives, pigments, drugs, alloys as well as the chemicals in common use. Discours de la Nature de Pair.-de la Vkgktation des P1antes.-Nouvelle Dicouverte touchant la Vie: By EDME MARIOTTE. (Paris, 1923 : Gauthier-Villars et Cie. Pp. I 18. This is another volume in the Series “ Les Maitres de la PensCe Scientifique.” Physicists will greatly welcome a reprint of Mariotte’s famous essay on the Nature of Air in this cheap and haqdy form.By C. A. Mitchell. 1924 : Crosby, Lockwood & Son. Pp. 271. Price 2 5 s . )BOOKS RECEIVED 949 The Thermal Properties of Ethyl Chloride. A special report by the Engineering Committee of the Food Investigation Board. (Published by the Dept. of Scientific and Industrial Research. Pp. 35. Price 13s. 6d. To be obtained from H.M. Stationery Office.) Studies from the Plant Physiological Laboratory of Charles University, Prague. Vol. I. Edited by Professor Dr. B. N~MEC. (Published by the University, Prague. The Formation of Transverse Fissures in Steel Rails and their Prevalence on Certain Railroads-Report of the Interstate Commerce Commission. (Published by the Bureau of Safety, Washington. Third and Final Report. (Published by the Department of Scientific and Industrial Research. Pp. 30. Porosity. Contributions from the Department of Ceramic Engineering, Univer- sity of Illinois. (Reprinted from the Journal of the Americari Ceramic Society.) Abstract Bulletin of the Nela Research Laboratory. National Lamp Works of General Electric Company, Cleveland, Ohio. Vol. I., No. 3. October, 1922. Vol. XI. A record of investigations undertaken by members of the Manchester College of Pp. I I 9.) Pp. 169.) Mine Rescue Apparatus Research Committee. Price IS. net. To be obtained from H.M. Stationery Ofice.) The Journal of the Municipal College of Technology, Manchester. Technology.ABERDEEN : THE UNIVERSITY PRESS

ISSN:0014-7672    

DOI:10.1039/TF9241900948

出版商:RSC    

年代:1924

数据来源: RSC