摘要:

JANUARY, 1905. Vol. XXX., No. 346. THE ANALYST. PROCEEDINGS OF THE SOCIETY OF PUBLIC ANALYSTS. THE monthly meeting of the Society was held on Wednesday evening, December 7, in the Chemical Society’s Rooms, Burlington House. The President, Mr. Thomas Fairley, occupied the chair. The minutes of the previous meeting were read and confirmed. Certificates of proposal for election to membership in favour of Messrs. P. Edgerton, J. McLeod, G. A. Pingstone, and A. W. Thorp, were read for the second time ; and certificates in favour of Messrs. William Ackroyd, F.I.C., Crossley Street, Halifax, Public Analyst for the County Borough of Halifax, and John Haslam Johnston, M.Sc. (Vict.), F.I.C., Public Offices, .Hampton, Middlesex, Chemist and Bacteriologist to the Hampton Urban District Council, were read for the first time.Messrs. C. G. Moor, M.A., and W. P. Skertchly mere appointed auditors of the Society’s accounts for the year 1904. THE PRESIDENT announced that the following nominations had been made by the Council for the election of Officers and Members of Council for 1905 : President.--E. J. Bevan. Past-Presidents (limited by the Society’s Coizstitution to ten in nunzbeY).--M. A. Adams, F.R.C.S. ; A. DuprB, Ph.D., F.R.S. ; Bernard Dyer, D.Sc. ; Thomas Fairley ; W. W. Fisher, X.A. ; Otto Hehner ; Alfred Hill, M.D. ; J. Muter, Ph.D. ; Sir Thomas Stevenson, M.D., F.R.C.P. ; J. Augustus Voelcker, M.A., B.Sc., Ph.D. Vice-Presidents.-L. Archbutt, B. Kitto, W. J. Dibdin. Hon. Treasurer.-E. W. Voelcker, A.R.S.M. Hon. Secretaries.-Alfred C. Chapman, P. A. Ellis Richards. Other Members of Council.-Julian L. Baker, R. Bodmer, R. Hellon, Ph.D., A.R.S.M., G. T. Holloway, A.R.C.S., J. €3. B. Jenkins, E. W. T. Jones, S. Rideal, D.Sc., Alfred Smetham, J. E. Stead, R. T. Thomson, L. T. Thorne, Ph.D., John White. THE PRESIDENT said that a special meeting of the Society would be held on January 11, 1905, when a discussion on the subject of ‘‘ Brandy ” would be opened by Mr. Hehner. The following papers were read : ‘‘ Some Recent Abnormal Milk Results,” by Sidney Harvey ; “ Electric Furnaces for Laboratory Use,’’ by Bertram Blount ; and a (‘ Note on Commercial Amy1 Alcohol,” by H. Droop Richmond and J. A. Goodson.

ISSN:0003-2654    

DOI:10.1039/AN9053000001

出版商:RSC    

年代:1905

数据来源: RSC

摘要:

2 THE ANALYST. THE MICROSCOPIC EXAMINATION OF METALS. BY J. H. B. JENKINS AND D. G. RIDDICK. (Read a t the Meetiqzg, April 13, 1904.) THE paper deals mainly with the microscopic examination of mild steel, but the principles remain the same for all metals. In the suggestions we make respecting the preparation of the metallic sections for examination and the manipulation generally, we follow our own experience. Probably in many cases better methods exist or will be devised, and undoubtedly different metals require some modifica- tions of treatment, according to their hardness, etc.; but we believe that the suggestions we offer will be found generally reliable and simple. As to the size of the metal section, unless there be some special reason for examining an extensive area, of the metal, it is well to keep the surface to be polished and prepared as small as possible.The work of getting a satisfactory polished surface on a large section is very great and tiresome. A piece of metal about i$ inch thick by 4 inch or 3 inch square is quite large enough in ordinary cases. Before studying wrought irons or very high carbon steels it is well to become familiar with the features of mild steel of, say, from 0.2 to 0.4 per cent. carbon content. A half-dozen re-examinations of such a piece of mild steel, watching the changes of structure which attend differences of heat treatment in a muffle furnace, will familiarize the mind with the subject better than endless description. Those who have large numbers of specimens to examine will probably get a polishing machine, of which there are several varieties on the market; but the majority of more casual workers will be content with hand-polishing.This consists in preparing the surface with a smooth file, and then rubbing it on emery- cloths of increasing grades of fineness, finishing up with, say, Hubert’s ‘( 0000 ” emery-paper. A final passage over some wet best quality rouge, laid on parch- ment or fine leather, completes the preparation. Care must be taken to avoid dust falling on the fine emery-papers and parchment. The unaided eye, after some training, can detect the development of the structure during the final stages of the polishing by reason of the harder parts standing out in relief. It is often well to examine the polished specimens at this stage under the microscope, for some features can be seen more clearly in the polished than in the etched section.As instanses of this we may mention sulphide and slag flaws in iron and steel, and cupous oxide (a usual constituent) in commercial coppers. I n the latter case the cuprous oxide can be seen located in little pits in the polished section ; by vertical lighting it appears as dove-coloured dots, and as brilliant, ruby- like particles by oblique illumination. These particles of cuprous oxide can also be seen with a low-power objective in a roughfracture of the copper. The etching of steel is conveniently done by dipping the polished surface into a saturated solution of picric acid in alcohol. About a half minute’s immersion is generally enough, but the right time must be determined by reference t o theTHE ANALYST.3 microscope. Next to this picric acid solution, we prefer a cold, filtered infusion of liquorice root, to which is added a little recently-precipitated calcium sulphate ; a piece of parchment laid on glass is moistened with this, and the polished metal surface rubbed very lightly to and fro over it. The drawback to the use of this etching agent is its tendency to decompose. Another agent sometimes useful is strong nitric acid ; the polished surface of the steel or iron is touched for a moment on the surface of the acid, immediately removed, and flooded with water. The nitric acid is useful for deep etching or for picking out the grain junctions, but is not well under control. I n some cases heat-etching (heat-tinting) is useful, trusting to the difference of rate of oxidation or colour of the oxides to distinguish the constituents.Cast irons and many alloys can be conveniently etched in this way. The heat oxidation is generally effected by laying the specimen on a heated iron plate. It must be remembered that the primary function of etching is the development of features which do not appear, or only slightly, in the unetched section. Some features are, however, best seen before etching, some with slight etching, whilst others require deep etching, and the etching agents will be selected accordingly. I n mounting the specimen it is important that the surface should be strictly parallel with the microscope stage. A simple little stepped contrivance, devised by Stead, is very useful for this purpose.A couple of them are represented near the feet of the microscope in Figs. 5 and 6. To make it, two sets of inch-wide strips of plate glass (of uniform thickness) are cut, the strips being of such decreasing lengths that when laid one on the other at opposite sides of a stout base plate of glass they form a double series of steps with a clear space between. The glass strips are fastened in position by Canada balsam. The metal specimen is placed so that its prepared surface rests on the base plate between the steps; some heat-softened cement (a mixture of equal parts of beeswax and rosin) is put on the centre of a microscope slide, and this is forthwith pressed down on to the back of the specimen until the ends of the slide rest on an opposite pair of the steps. By this means the prepared surface of the nietal is mounted parallel to the microscope slide.Next comes the question of illumination. Metals, being opaque, cannot be illuminated by transmitted light ; they must be lighted from above. And here we would point out that an entirely different effect is produced according to the method of illumination. With oblique illumination one gets, as it were, bhe negative effect of what is got by vertical illumination (compare Figs. 3 and 4). This may lead to some confusion, and it is best to keep as much as possible to vertical illumination; indeed, oblique illumina- tion is not practicable with high-power objectives. Of methods of vertical illumination two are well known, and both depend upon the admission of a normal ray of light into the body of the microscope just above the objective, this ray of light being then reflected down on to the object which it illuminates.I n the one class of illuminators (Nachet's, etc.) this reflection is brought about by a right-angled prism, fitted inside the microscope, whereas in the second (Beck's) the reflection is effected by a little plain disc of glass, which can be turned round inside the microscope tube until, at an angle of 45" with the entrant ray, the latter is reflected down on to the object. The specimen is now ready for examination.4 THE ANALYST. All the vertical illuminators depending on the use of the right-angled prism are not equally effective, and we recommend that they be teEted practically before they are purchased.A well-constructed one gives beautiful illumination ; but, nevertheless, if it be a choice between the two types of illuminators, we recommend Beck’s as being of more varied utility, and especially serviceable with high-power objectives. Beck’s illuminator cannot be used satisfactorily with low-power objectives-say 1+ to 2 inch objectives. For these powers Stead has devised a simple illuminator depending on the same principle; but it is placed below the objective. It consists of a microscope slide, fixed or clipped in any convenient way above the metal section, and at an angle of 45”. The under surface of this slide is made to serve as a reflector, to throw a ray of light vertically down on to the section beneath. For the photography of the metallic sectione nearly every authority emphasizes the value of apochromatic objectives, but our experience with them is not satis- factory.There is a want of flatness of field with all apochromatic objectives which have come into our hands, so that generally it is impossible to get more than a minute portion of the centre of the field sharp. We prefer ordinary objectives, though they require careful selection, from whatever source they come. In taking photomicrographs, the Welsbach gas-burner is a convenient source of illumination. The electric arc- lamp, of course, reduces the time of exposure, but it is usually not so steady, and is trying to the eyes in the preliminary focussing. We find LumiBre’s orthochromatic plates, series A, to give us the best results, and for printing we use ‘‘ glossy ” gaslight paper. The camera arrangement is shown in Figs.5 and 6. For the preliminary focussing the camera is swung aside (Fig. 5), so that the eye can be applied directly to the microscope. Over the eye-piece of the microscope a collarette of black cloth, with a stiff piece of cardboard behind, is seen. When, after the preliminary focus- sing, the camera is put beck into its final position, this cloth and cardboard press lightly against the end of the camera, and form a light-tight connection. The final focussing on the ground-glass screen is done by means of a tripod lens (vide Fig. 5), or by an ordinary reading lens. According to the degree of the illumination and the number of diameters of magnifications, some modifications may prove useful to assist sharp focussing.Oiling the ground-glass screen, to increase its transparency, may be tried, and for very high magnifications we have found it advisable to discard the use of the ground-glass screen altogether, and to put a sheet of cleay glass in position in the ‘6 dark slide,” focussing as before by the aid of a magnifier. Working for 150-diameter photographs, we use a $-inch objective and a x 5 eye-piece. With a piece of mild steel, LumiBre’s plates, and Welsbach light, about three minutes’ exposure is sufficient ; with limelight, about 1 minute ; and with arc-light, far less. Increased stretch of camera is generally to be recommended, rather than the use of higher-power eye-pieces. Sorby’s pioneer work in the microscopic examination of steel is of the highest value, and his papers, to be found in the Joz~rnal of the Iron and Steel Institute, 1886, 1887, should be carefully read.Since that time the structure of steel has been If more light is desired, the limelight is very good.THE ANALYST. 5 studied by many workers, and the different morphological elements have received distinguishing names. For a full account, reference may be made to the successive volumes of the Metallographist and to the Reports of the Alloys Research Committee of the Institution of Mechanical Engineers. It is now accepted that a simple binary metallic alloy, in cooling from a state of molten solution, acts like a solution of salt in water. On cooling the latter solution, the excess ingredient, whether it be salt or water, commences to crystallize out at a certain temperature, which depends upon the strength of the solution.This crystallization out of one constituent continues with the fall of temperature until, at a definite low temperature, which is fixed, whatever may have been the initial composition of the solution, so much of the excess ingredient has been removed that the still remaining mother liquid is saturated with respect to the two ingredients, water and salt. The next fall of temperature causes the whole of this remaining mother liquid to crystallize out as a minute mechanical mixture of salt and ice. This mechanical mixture of crystals of salt and ice thus produced during the final stage of solidification is termed the eutectic. Its composition-the percentage of salt and ice it contains-is invariable.I t is similar in the case of simple binary metallic alloys-e.g., in the case of copper-silver alloys cooling from a molten condition-the excess ingredient crystallizes out progressively until finally, at a definite, lower temperature, the mother liquid is saturated with respect to the two metals, and thereupon there is a co-precipitation of crystals of copper and silver side by side to form a mechanical mixture called the eutectic, which, of course, has a fixed composition. If an etched section of such a copper-silver alloy be microscopically examined it will show the excess metal, whether copper or silver, which has solidified at a higher temperature, as a background, with here and there the eutectic of alternate, interstratified plates of copper and silver, which can be readily identified.This appearance of interlamination of crystal plates of the constituent metals is common to very many eutectics, but in other cases or under different conditions the mixed crystals appear more granular or confused. I n caBes of other alloys-e.g., zinc and copper alloys-the metals form definite chemical compounds with one another, so that we may have the case of one chemical compound dissolved in an excess of another, or separating from it on cooling. And the effects become more complicated when third metals, or compounds, are present. In other cases, when the elements of an alloy are isomorphous in crystalline structure, the constituents may not be separately identifiable under the microscope.I n the case of steel-ie., iron-carbon alloys containing up to about 1-5 per cent. carbon-we have to consider not only the solidification of a liquid solution, but, at much lower temperatures and when the metal is solid, the separation of bodies from solid solution, as well as other changes. I n the diagram shown in Fig. 7, in which the temperature and carbon content of the steel are co-ordinates, the temperatures at which such changes occur for different qualities of steel are shown. The following are the points of special interest in the diagram, SO far as the final microstructure of the steel is concerned. We give the views which are generally accepted. The temperatures of initial solidification of the iron are shown6 THE ANALYST.in the top line. Below the next line, which meets the first at 1,600" C. or there- abouts, there exists a soZid solution of carbon in iron. At lower temperatures- say 1,000" C. to 1,100" C.-the carbon, which at higher temperatures existed as a solution in iron, now enters into a fresh condition, and although still remaining in solution, exists there now as a definite carbide of iron, Fe,C (cementite). Dis- regarding here the allotropic changes in the iron, we may broadly take it that a t 1,000" C., or thereabouts, we have to deal essentially with a solid solution of the carbide of iron, Fe,C (cementite), in iron (ferrite). If the carbon in the steel is less than about 0.8 per cent.-or, we may sayt rather, if the cenzeiztite (Fe,C) is less than about 12 per cent.-then the iron (ferrite) is the excess ingredient ; and as the temperature of the solid solution cools further, the crystals of almost pure iron (ferrite) separate out (cf.diagram, Fig. 7), leaving a mother solid, which becomes continuously richer in cementite, until, at a temperature of about 680" C., the mother solid is saturated with respect to the two constituents, ferrite and cementite, and the next fall of temperature witnesses a co-crystallization of these two con- stituents, generally in minute interstratified plates. The areas of the steel in which this co-separation of ferrite and cementite has taken place are known as peadite areas. When examined under very high magnification, the composite nature of psarlite can be detected. Pearlite, being formed from a solid solution, is called an eutectoid, to suggest at once its relationship to eutectios, which are similarly formed from Ziqz6id solutions.Under the microscope-say 100 diameters-a polished and etched section of very mild steel should show a field of ferrite, or nearly pure iron, appearing white, with here and there the almost black areas of pearlite, in which latter something of its composite character may already be indistinctly seen (vide Figs. 3 and 11). The total extent of the pearlite naturally becomes greater with the increasing per- centage of carbon (cementite), until, when it reaches about 0.8 per cent. carbon, the whole field consists of pearlite. When the carbon exceeds 0.8 to 0.9 per cent., the cenzeittite becomes the excess ingredient, and appears as the white constituent of an etched section, generally standing in relief owing to its hardness, the pearlite being black, as before, This refers to slowly-cooled steels; but the physical properties of steel are altogether altered by the heat treatment to which it has been subjected; and this can be judged far better by the microscope than by chemical analysis, though both are essential.For example, if a steel containing, say, 0.3 to 0.4 per cent. carbon be reheated to a temperature just short of melting, and kept there a little time, it becomes '( burnt " and mechanically unreliable. I n such a burnt steel one would see under the microscope minute internal cavities or fissures here and there in a section, and somewhat coarse junction markings between the enlarged grains.If another piece of the mild steel were heated to, say, 900" C., and then quenched in water, it would be "hardened"; it would be very brittle, and not scratchable by a file. Examined under the microscope, the structure of this hardened steel will be quite abnormal, but very characteristic; the whole field will show a confused angular or criss-cross structure, called iizarteizsite (vide Figs. 31 and 36). If the same piece of hardened steel be next heated for, say, a quarter ofTHE ANALYST. 7 an hour at about 350" C. and cooled, it would lose much of its hardness and brittle- ness, and become (' tempered," and the microscopic structure will be found to have lost more or less completely the angular arrangement of martensite (cf. Fig. 38).If this piece of tempered steel be heated again to 350" C., and kept at that temperature for a longer time, the structure passes more completely from the martensite type, and gradually acquires the character of minute granular pearlite (cf. Fig. 40). The physical properties become progressively modified corresponding to these micro- scopic changes. This property of steel is explained as follows: When the steel is quenched from 900" C., or thereabouts, it is cooled so quickly that the changes which would otherwise have taken place, such as the separation of ferrite and cementite to form pearlite, are prevented, and we have at ordinary temperature a metal representing more or less the condition of steel which existed at the high temperature from which it was quenched. This condition of the steel, represented in the martensite structure, is, however, unstable at low temperatures, and reheating to a com- paratively low temperature-300" to 400" C.-causes a gradual reversion to a more normal condition, the reversal becoming more complete in proportion as the ternper- ing heat is higher (up to, say, 600" C.) or the time of exposure is increased.A tempered steel has properties intermediate between those of a hardened and an ordinary steel. Still considering such a piece of 0.3 to 0.4 per cent. carbon steel, if it were heated to, say, 1,000" C., kept for a long time at that temperature, and then allowed to cool down very slowly till past the '( critical " temperature (about 680" C.), its structure would finally be very coarse. If this were reheated, however, for even a few minutes, to above the " critical " temperature, the coarse structure would be quite broken up, and, on cooling, a comparatively fine structure would result (wide Figs.27, 32, etc.). But if the reheating of such a piece of steel were not to get above 680" C., there would be no change of structure from the previously coarse to a fine- grain condition. Whilst with steels in ordinary condition 680" C., or thereabouts, marks sharply the temperature at which the grain structure is entirely and quickly rearranged, still, if a piece of mild steel be allowed to 6 c soak " for a very long time--say, some days or a week-at a temperature somewhat belozu 680" C., as is done in some methods of annealing, an action goes on slowly in the steel corresponding to the growth-the effect of surface tension-of the larger crystals and disappearance of the smaller, when crystals of salt stand in contact with their mother liquor.I n a kindred way the crystal plates of cementite in the pearlite areas tend at a temperature somewhat below 680" C. to grow or unify, and to be represented by irregular areas of massive cementite (cf. Figs. 13 and 14). Any internal mechanical stresses in the steel due to "working" at too low a temperature might be relieved by such low temperature annealing, but the steel would be likely to have a somewhat low elastic limit. If a piece of mild steel were heated for a short while to 800" to 900" C., at which temperature the cementite would go uniformly into solution, and then cooled very quickly, but not so quickly as by quenching in cold water, the rate at which the steel passes by the critical temperature, about 680" C., is still too great to allow of the satisfactory co-separation of ferrite and cementite to form well-defined pearlite.It is I n this way it differs entirely from a '( hardened " steel.8 THE ANALYST. a condition preliminary to the formation of pearlite that the carbon at the particular point concerned shall have accumulated until it has a local richness corresponding to the eutectoid proportion, about 0.8 per cent. This is impossible in a mild steel con- taining, say, 0.3 to 0.4 per cent. carbon, so long as the cementite is uniformly dissolved in the mass of the metal; but during the very rapid cooling there would be an infinitude of points at which separation of ferrite (free from carbon) takes place, and from these points there would be an extrusion of the cementite so as to create a local richness in the immediately contingent metal until the carbon there reached the eutectoid proportion, and a slight separation of pearlite would follow.Further away there would be places where a condition of solution of cementite still existed, no evident separation having taken place so far as can be seen by the micro- scope (cf. Figs. 15, 25, 32). A steel which has been cooled a t such a rate as checks the separation of ferrite and pearlite, and leaves more or less of the cementite still in solution, exhibits, according to its rate of cooling, a considerable diversity of microstructure ; it may touch martensite on the one hand, and ferrite with pearlite on the other.Such steel is said to be sorbitic, and any micro-areas in it in which there is evidence by staining that the carboniferous constituents reside, but which cannot be resolved by the microscope into pearlite, may be said to be sorbite. The sorbitic condition may be attained by direct quenching in hot water or oil, or the quenching may be followed by a second process of limited exposure to a temperature of, say, 600" C.-as it were, a process of over-tempering. This sorbitic structure is worthy of attention, for steel-makers are now devoting much attention towards developing this condition in steel intended for engineering purposes. A sorbitic steel may be regarded, perhaps, as intermediate in mechanical properties, as well as in microscopic appearance, between tempered steel and ordinary annealed steel.I t s total strength is increased, but its elastic limit is increased in a still higher ratio by this treatment. Thus, in general, the changes of structure in a steel which attend differences of heat treatment-of which many illustrations are given in the accompanying figures- are readily followed by the microscope, and since there are modifications of mechanical qualities corresponding to all these changes, it will be evident that the microscope is an invaluable aid to chemical analysis, enabling us to foretell the physical properties of any specimen of steel, or to account for a local weakness. The value of the microscope is not so marked in respect to the other ordinary elements of steel. I n the case of sulphur, however, the r81e played by manganese is seen.If manganese be absent the sulphur exists as a fusible sulphide of iron, often lying as a brittle constituent between the junctions of the crystalline grains, somewhat as shown in Fig. 8. If sufficient manganese be present, however, it seizes the sulphur and forms a less fusible sulphide, and then appears-so far as we have observed-invariably locked up in the ferrite areas, almost as though the particles of sulphide of manganese had served as nuclei round which the ferrite grains had crystallized. An impurity in this condition is far less likely to seriously affect the strength of the steel than when it resides at the grain junctions. Another property of the manganese in steel may be here mentioned. High manganese often, but not invariably, renders the pearlite areas larger than would correspond to the carbonTHE ANALYST.9 content, and more or less sorbitic in character (cj. Fig. 15). Apart from combination as sulphide, the manganese seems to reside largely 3s a carbide in the pearlite areas. Phosphorus and silicon in any quantity likely to be present in B mild steel appear to reside in the ferrite, and at present we cannot point with confidence to any definite features under the microscope to correspond with them; but it is probable that further experience will show special properties in the ferrite grains--e.g., difference of action on being etched or heat-tinted- to correspond with the content and condition of these impurities.When the phosphorus is present in large quantities, as well as much carbon, it leads to the formation of a phospho-eutectic of characteristic appearance (vide Fig. 3). This is a usual feature of cast or pig iron. Of course, if the phosphorus or silicon were oxidized, it would appear as slag in the steel. The examination of a metal or alloy is generally conducted with a view of its past history or its intended use. In case of the failure of a metal in service the examination of sections in the immediate neighbourhood of the point of failure often shows a purely local defect to which the failure is attributable; or the structure of the metal, as a whole, may be bad. A small-grain structure and an absence of linear arrangement is generally desirable, and this should be secured by proper annealing. If cooling curves can be consulted with respect to any alloy, they help in the inter- pretation of the microscopic appearance.It will be well to examine the sections when simply polished, and then when etched to different depths. I n the case of steels, for instance, it is not often that the degree of etching which brings up the pearlite into best definition will enable the junctions between the ferrite grains to be seen; these generally require much deeper etching. It is important to examine these grain junctions with suitable (generally high) powers. Impurities in alloys and metals often lie along these grain junctions, and constitute sources of weakness in the metal. I n other cases, however, these junctions are of the toughest character, and the grains will themselves split across rather than the junctions give way or open.Often it is well to get a thin disc of the metal, which is polished, and then bent in a vice or a V-block. A fresh examination of the bent surface will often show whether a metal is stronger in the grain or in the junctions. EXPLANATION OF FIGURES. I n the photomicrographs it may be taken, unless otherwise stated, that the sections of metal are polished and etched and vertically illuminated. Figs. 1 and 2 : Iron crystals. Actual height of No. 2 crystal is 7 inches. When a metal solidifies, such crystals, starting from an infinitude of points, continue to grow until they are arrested by encountering other growing crystals. I n consequence of this interruption to crystal growth, the crystalline nature of the grains of steel is rarely evident in their contours; but the internal orientation and other crystal characteristics of the grains are evident when the metal is strained.Free iron crystals, such as are illustrated, are found fringing hollows in steel castings where the crystal developnient has been uninterrupted. Figs. 3 and 4 : Pig-iron. Illustrates the different effect of vertical and oblique illumination of the same section. Fig. 3 is vertically illuminated. I n it the graphite10 THE ANALYST. plates form white, almost straight lines; they are surrounded by nearly black pearlite, and then come irregular white areas of a phospho-eutectic. Fig. 4 is of the same section, but obliquely lighted. In Fig.5 the camera is swung aside for preliminary focussing; in Fig. 6 it has been put into position. x 100 diameters. Figs. 5 and 6 show camera and microscope. Fig. 7 : Cooling curves of iron-carbon alloys (steels). Fig. 8 : Wrought iron, practically carbonless. Has been heated almost to ( ( burning ”-point. The dark specks in this axe not of pearlite. Some slag impurities lie along some of the junctions of the ferrite grains, and some highly minute crystal cubes of iron exist in a few of the grains. Dark pearlite areas can now be seen on a general ferrite background. (Cf., Fig. 13, which shows the same steel, in which the pearlite is largely replaced by cementite.) Fig. 10 : Mild steel, 0.18 per cent. carbon. The areas of pearlite become greater in accordance with increased percentage of carbon.Fig. 11 : Mild steel, 0.4 per cent. carbon. The dual structure of the pearlite can be indistinctly seen. Fig. 12 : Cemented steel. The carbon in this is much beyond 0.8 per cent., and here we have cementite as the white constituent, pearlite constituting the general background. x 150 diameters. Fig. 13 : Cementite produced in very mild steel (0.05 per cent. carbon ; wide Fig. 9) by annealing below the critical temperature. Fig. 1 4 : Cementite produced in mild steel, 0.17 per cent. carbon, by long annealing at about 600” C. Figs. 15,16, and 17 illustrate steel containing high manganese (1.66 per cent.) and sulphur (0.13 per cent.). The sulphide of manganese will be seen to reside in the ferrite. The mechanical working of the steel at a very high temperature has drawn out the sulphide into threads, as can be seen in the longitudinal section (Fig.15), whereas in the transverse section (Fig. 17) the threads, being cut across, appear 8s dots. Note, too, that the extent of the pearlite is greater than would correspond to the content of carbon (0.27 per cent.). This enlarged structure is cften found in steel containing high manganese. The steel is somewhat sorbitic. Fig. 16 is of the same steel, but illustrates that the sulphide threads can be even more plainly seen in the polished section before etching. I n nearly every mild steel such threads of sulphide or slag are evident to a greater or less extent in the longitudinal sections. If the “working ” of the steel in manufacture has been continued down to a low temperature (below the critical temperature), the grains of pearlite will also be drawn out, so that there is a general alignment in the section. If the steel, after such working, be again annealed, the pearlitic structure will be quite broken up at temperatures which will be far below those that are necessary to alter the features of the sulphide threads, which latter will still remain, therefore, to show the direction of ‘( working.” It is probably due to the relative permanence of position of these impurities that there is a tendency for lines of ferrite to reappear where they previously existed, although the steel has been reannealed.The contours of the crystal grains are very distinct. x150 diameters. Fig. 9 : Very mild steel, 0.05 per cent.carbon. x 150 diameters. x 150 diameters. x 150 diameters. x 150 diameters. x 300 diameters. x 150 diameters.THE ANALYST. 11 Fig. 18 : Enlarged view of grain of pearlite. It appears to be made up of alter- nate micro-plates of hard cementite and soft ferrite. Etching eats away, more or less, the soft plates of ferrite, and the nearly black appearance of etched pearlite is due to shadows cast by the projecting edges of the minute cementite plates. x 350 diameters. The oxygen, which makers purposely leave in commercial coppers, resides in minute pits as ruby-red cuprous oxide (or, it may be, as an eutectic of cuprous oxide and copper). The consequent breaking up of the solid continuity of the copper would appear to be disadvantageous ; it is said, how- ever, to be necessary to counteract the bad effect of certain metallic impurities, such as lead or bismuth. The left-hand figures show the coppers polished only ; the right- hand figures show the same after etching with nitric acid.The oxygen-content of the three coppers is respectively 0.01 per cent., 0.1 per cent. (about average quantity), and 0.33 per cent. ; the latter is, undoubtedly, excessive, and the metal brittle as a consequence. x 65 diameters. Fig. 20 : Burnt copper. A ‘‘ burnt ” metal generally shows big grains and a coarsening of junctions. x 25 diameters. Oblique light. Fig. 21 : Small V-block of copper (0.33per cent. 0.) which wag exposed for about three-quarters of an hour at somewhat low red heat to the action of hydrogen ( c j .hrchbutt’s paper on determination of oxygen in copper, ANALYST, October, 1900). The block was then cut across and the section polished, The line to which the oxide has been reduced is clearly marked; the darker interior portion is still charged with the oxide, but the outside portion shows none of it under the microscope. The depth to which the action extends seems proportional to the time of exposure. x 10 diameters. Oblique light. The action of the hydrogen, besides reducing the oxide, also seems to develop the grain contours; possibly the gas finds entrance to the interior of the copper largely past the grain junctions. Fig. 23 : Piece of mild steel, polished, then heated in hydrogen as above ; the picking out of the grain-junctions is again apparent. Fig.24 : Copper meshed with small percentage of bismuth. Fig. 25: Piece of mild steel, 0.35 per cent. C , which has been specially “ sorbitized ” by manufacturers. The structure a t some places approaches martensite, but more generally it shows a structure, as represented in Fig. 25, which is inter- mediate between that of Fig. 38 and that of Fig. 40. Fig. 26 : Mild steel, 0.43 per cent. C, with strongly angular structure, not properly annealed. x 150 diameters. Fig. 27 : Same steel as Fig. 26 after annealing. x 150 diameters. Figs. 28 and 29 : A mild steel shaft (0.19 per cent. C) showed EL rninute ‘‘ hair- line” flaw on surface. It was condemned, and broken across at the place of the flaw. The fracture showed at one point of its circumference a, projecting lip (B, Fig.28). It was cut through along the lina A B (Fig. 28) so as to show the lip in profile. This section, when polished and etched, showed that, whereas the direc- tion of grain in the main body of steel was longitudinal, as indicated by the arrows, yet near the lip there is a distinct sweeping back of the grain into the lip. The Fig. 19: Oxygen in copper. Fig. 22 : A polished section of copper was heated as above in hydrogen. x 150 diameters. x 150 diameters. x 65 diameters. x150 diameters.12 THE ANALYST. explanation would appear to be as follows : When the red-hot shaft was being worked under the hammer it was subjected to a process by which its diameter was reduced. I n the course of this reduction a portion of the metal got puckered up, then folded over and hammered down flush.The temperature of the metal at this time was too low to let this folded-over portion weld with the mass of metal beneath, so it remained as an ‘‘ overlap.” Figs. 30 and 31 : Fig. 30 shows the section through the chimb-joint of an elec- trically-welded drum. I t is made up of four thicknesses of mildest steel the flush edges of which have been fused together by the momentary impinging of an electric arc. The metal at the edge was thereby instantly raised to boiling temperature of steel, from which the body of cold metal chilled it with almost as great rapidity. The line to which fusion has extended is clearly seen. Fig. 31 shows the structure at the line to which the fusion extended; the upper part shows a martensite structure, whereas in the lower part the original structure of normal very mild steel remains unaltered. The line of separation of the two structures is very sharp.The diameter of the disc of metal represented in the photomicrograph (Fig. 31) is less than a millimetre. Fig. 32 : Illustrates the changes of structure produced by simple heat treatment in a piece of mild steel (0.35 per cent. C). Fig. 33 : Cast-steel bar (0-32 per cent. C and 0.34 per cent, Si). This imperfect bar was tested to destruction, and broke at two places a few inches apart. The frac- tures thus exposed were entirely diil‘erent, the one being very fine-grained (AA, the outside figure), whilst the other was coarsely crystalline, (BB, outside figure). The piece was then sectioned from the one fracture to the other, and the section polished and etched.I t will be seen that the transition from the fine to the coarse structure is fairly sharply located between “ 3 ” and “4.” I n the lower figure are photomicrographs of the steel, x25 diameters, taken at the points 1, 2 . , . 8. I t is manifest that if the two frac- tures had taken place within 3 inch of each other at 3 and 4, theone fracture would still have been very fine and the other very coarse, The explanation of the difference of structure is as follows : the main portion of the bar, represented by BB fracture, had not been annealed to any sensible extent, and hence its coarse structure. The other, AA, end of the bar had been reheated for further working. In this reheating the temperature to the left side of 3 had risen above the “ critical ” point, and a breaking up of the original coarse structure had followed; but on the right side of 4 the temperature had not reached the critical ” point, and the coarse structure remained.Figs. 34 to 41 will show variations of structure which have attended further heat treatment of this steel. Figs. 34 to 41 : Several strips of the steel shown in Fig. 33 were taken, as repre- sented between Figs. 1 and 8, and they were subjected to different heat treatments. Fig. 34 shows the fine structure, whilst Fig. 35 shows the coarse structure, corre- sponding respectively to 1 and 5 of Fig. 33. One of the strips was heated to very high temperature, almost At each part of the strip we had the structure (martensite) of hardened ” steel (Fig. 36) ; it could not be “ touched ” with a file.This hardened strip was next heated at 350” C. for a quarter of an hour ; it was thereby tempered,” and lost much of its hardness. The x 65 diameters. x 150 diameters. The centre figure shows the etched section full size. burning,” and then quenched in water.13 THE ANALYST. structure was now very confused, but still showed traces of martensite (Fig. 38). It was heated again to 350" C. for six hours, this continued the tempering process, and the steel now had the structure represented in Fig. 40. It is difficult to give a name to this structure which is not open to objection ; by some it is called minute granular pearlite. When this same piece of steel is heated up well above the critical tempera- ture, and allowed to cool somewhat quickly, it gets the structure of Fig.41-not very different to Fig. 34. A portion of the coarse end of a strip of the steel was heated up to 350" C. for six hours. It is not, of course, the same actual section shown in the two views. It had to be repolished after the heating. Another strip of the original steel was taken, heated up to about 850" C., or thereabouts, for a few minutes, and then rapidly cooled between two iron blocks. All parts of the steel had the very fine-grain structure represented in Fig. 39. It must be understood that small pieces of metal can be heated and cooled rapidly with comparative ease ; but manufacturers dealing with large and irregular masses have many practical difficulties to deal with, and allowance must be made for this.What one would desire is not always what we can fairly expect in the way of structure in large masses 0: steel. But quite apart from the question of chemical purity, there is a general recognition now on the part of the best makers of the value of a fine-grain microscopic structure to secure the best properties in steel. I t showed no alteration of structure (cf. Figs. 35 and 37). DISCUSSION. The PRESIDENT (Mr. Fairley) said that with regard to this subject he was very much in the position of a learner. Among those present, however, whose work was specially well known in connection with it was Professor Huntington, whom he would ask to be good enough to open the discussion. Professor HUNTINGTON said that, as a matter of fact, all who had to deal with metallurgy were very much in the position of learners.There was an enormous amount of learning for them to do. He thought there could be no doubt that the microscopical examination of metals was indispensable if their structure and the treatment they had undergone were to be fully understood, and the paper which had just been read would be very valuable as an introduction to the subject for those who had not already gone into it, while one could not possibly get any harm in listening to such a paper as this even if one had studied the subject. The photographs were most admirable and interesting. In the case of such a paper it would not be fair to make any carping criticism-in fact, the paper was not open to it. The subject, however, was open to any amount of discussion.The difficulty was that one did not know where to begin or where one would end, and at the late hour which had been reached one hardly liked to begin. With regard to arc-lamps, these had been used in his own laboratory for some time with satisfactory results. He had begun by using oil, and from that had gone on to the use of the arc, so that he could not speak much about the oxyhydrogen light. The arc, however, was very useful if the necessary electric current was available. It was simple to handle and very effective, and the lamps were comparatively cheap. A good arc-lamp could be bought for about 23. The difliculty wm not so much with the lamps as with the carbons. The whole14 THE ANALYST. secret rested in the selection of suitable carbons free from ash.Bad carbons, owing to the ash which they contained, caused the light to flicker considerably, which at once destroyed the clearness of the photographs. H e had obtained very satisfactory carbons from Messrs. Siemens. Many people seemed to think that it was necessary to have some automatic arrangement, but he did not find that at all necessary. H e had only a hand arc-lamp, but the time of exposure was really so short that it was quite easy to regulate the arc, the consumption of carbon not being so rapid as to cause any difficulty. I n fact, although he had been quite prepared to get an automatic lamp if it were really found t o be necessary, he had not yet done so. With regard to copper, Heyn had done a great deal of work, having been perhaps the fir& to investigate the eutectic of oxide of copper and copper ; and there appeared every probability of an easy method being afforded in this way of actually estimating the oxygen present in otherwise pure copper.There was an actual eutectic, which was quite distinct, and it was perfectly easy to estimate practically by the eye, without going into fine measurements of areas, the amount of oxygen present. H e believed (but he spoke subject to correction) that that method was actually being used a t Woolwich at the present time as a quantitative means of estimating the amount of oxygen in copper, and in his own laboratory, without going very far into the subject, photographs had been taken connected with actual practical work, and it had been found possible to obtain a very close approximation to the amount of oxygen present.I t could be done roughly by simply comparing the photographs taken with Heyn’s diagrams-a number of photographs showing the effect of different amounts of oxygen. Some five-and-twenty years ago he had worked with Professor Guthrie on the subject of the cryohydrstes, as they were called by Professor Guthrie, who did not then use the term ‘( eutectic.” Professor Guthrie had thought these to be definite chemical coinpounds-an idea which he (the speaker) must say had not appealed to his mind at the time, as it seemed strange that any chemical compound should exist having hundreds of molecules of water. Later on Professor Guthrie went on to apply the same idea to alloys, and it was then that he originated the term “ eutectic,” which he applied to the lowest melting alloy in a combination of metals.Of course, the authors were quite right in comparing the two things, though Professor Guthrie originally did not use the term ( I eutectic ” at all in connection with the cryohydrates. Mr. BLOUNT said that it would not be wise at that time of the evening to speak at any length, but he felt-and he thought he might voice the congratulations of others also-that the only word that would properly describe the work that the authors had done, and the illustrations that they had given of it, was “ splendid.” The PRESIDENT expressed much pleasure in supporting what Mr. Blount had said. The Society was exceedingly indebted to the authors for the very lucid and interesting account they had given of this subject.There were many points that; one would like to talk about, but that must be reserved for a future occasion. Mr. ARCHBUTT said that he had brought two specimens which might perhaps be interesting, bearing upon the photographs which the authors had shown. I n pointing to the effect of oxygen in copper, Mr. Jenkins had remarked that, although it was undoubtedly useful, it was, perhaps, rather a pity that it should be there. One of the specimens which he (Mr. Archbutt) had brought had been made by melting electrolytic copper with 0.15 per cent. of lead. An attempt had been made to forgeTHE ANALYST. 15 it at a red heat, but it was practically unforgeable. The second specimen was a piece of copper containing the same percentage of lead as the first, but with the addition of 0.12 per cent.of oxygen, added in the form of cupric oxide, and this piece had forged perfectly well. He should like to ask Professor Huntington whether the method of estimating oxygen by the microscope was applicable to copper which had been mechanically treated, because cast copper containing oxygen presented a very different appearance from that of copper which had been rolled, drawn, or hammered. I n cast copper the oxide formed a mesh throughout the copper, whereas in copper that had been drawn, rolled, or hammered the oxide was distributed in the form of dots and bands, as shown in the authors’ photographs. I n the case of the copper to which lead had been added, but no oxygen, the lead was seen on microscopical exami- nation before hammering to be distributed throughout the crystalline grains in particles, which in some way or other caused the effect he had mentioned; whereas in the copper which contained oxygen as well as the lead, the whole of the lead had been drawn into the oxide network, which was presumably the reason why it was not deleterious in that piece of copper, while it was deleterious in the other piece in which it was distributed throughout the grains. He would like to add his hearty congratulations to the authors on having presented so interesting a paper and such excellent photographs. Professor HUNTINGTON said that Mr. Archbutt was no doubt correct in saying that there was a considerable difference in the appearance as regards the distribution of the oxygen between cast copper and wrought copper. It was not, however, a point that he had worked at much himself, though he had made some observations on it. A great deal of work required to be done on the oxygen question, but he had not had time to do very much himself. Indeed, it would probably take many months if one started on it at all. Mr. Ross said that in the apparatus used in a sulphate of ammonia manu- factory, the old saturator that had been in use for about twenty years wore very much better than a newer one made of much purer lead. The new one corroded at the seams, though the lead used for the seams and for the body was from exactly the same masg. Speaking from recollection, he thought there was not very much differ- ence in the two cases between the amounts of oxygen which the lead contained, but possibly microscopical .examination would have revealed some difference in the structure. Mr. JENKINS, in reply, said that it was evident that by examining a polished section of copper under the microscope a fairly good estimate of the percentage of oxygen could generally be made. The chief difficulty was that the oxide was not evenly distributed in the mebal sections. But whatever observations were made under the microscope, it would be necessary finally to compare them with determina- tions of oxygen made by some standard chemical method, such as ignition in hydrogen, as recommended by Mr. Archbutt. Mr. Riddick and he were grateful to the meeting for the attention with which the paper had been received. He desired to express his own indebtedness to Mr. Riddick, who was very largely responsible for the execution of the photographic work, and had brought a great deal of skill and patience to bear upon it. +I+**+%*

ISSN:0003-2654    

DOI:10.1039/AN9053000002

出版商:RSC    

年代:1905

数据来源: RSC

摘要:

16 THE ANALYST. REPORT OF THE COMMITTEE APPOINTED TO CONSIDER THE STANDARD- IZATION OF METHODS FOR THE BACTERIOSCOPIC EXAMINATION OF WATER. (Reprinted from ( ( The Journal of State Medicine," Aagust, 1904.) AT the Congress of The Royal Institute of Public Health, held in the University of Liverpool, in July, 1903, a resolution was carried, on the motion o€ G. Leslie Eastes, Esq., M.E., B.Sc., that it was desirable that a committee should be appointed to consider the methods employed in the bacterioscopic analysis of water, and, if possible, to draw up a scheme of uniform procedure for adoption in such examination, and to report to the next Congress of The Institute. The Council of The Royal Institute of Public Health, in accordance with this resolution, appointed a committee of the following gentlemen : Professor Rubert Boyce, M.B., F.R.S.(chairman) ; the President of The Royal Institute of Public Health, Professor William R. Smith, M.D., D.Sc., F.R.S. Ed. ; George M. Duncan, Esq., M.D. ; G. Leslie Eastes, Esq., M.B., B.Sc. ; John Eyre, Esq., M.D. ; Major W. H. Horrocks, R.A.M.C., M.B., B.Sc. ; William G. Savage, Esq., M.D., B.Sc. ; Professor G. J. McWeeney, M.D. ; Professor G. Sims Woodhead, M.D., F.R.S. Ed. ; and Professor R. Tanner Hewlett, M.D., D.P.H. (Honorary Secretary). REPORT OF THE COMMITTEE. All the members of the committee are in agreement that the minimal number of (a) Enumeration of the bacteria present on a medium incubated at room temperature (18-22" C.). ( b ) Search for Bacillus coli, and identification and enumeration of this organism if present.The committee regard these procedures as an irreducible minimum in the bacterioscopic analysis of water. The majority of the committee recommend in addition : (c) Enumeration of the bacteria present on a medium incubated at blood heat ( d ) Search for and enumeration of streptococci. The committee do not think it necessary as a r o a t i m measure to search for the Bacillus enteritidis sporogenes, but are agreed that in special or exceptional instances it may be advisable to look for this organism. procedures should be : (36-38" C.). THE COLLECTION OF THE SAMPLE. No special precautions beyond those generally recognised are suggested for taking the sample. The samples should be collected in sterile stoppered glass bottles having a minimal capacity of 60 C.C.In special instances it may be desirable to have much larger quantities. Unless examined within t h w e hours of collection the sample must be ice-packed. (The committee recognise that under all circumstances the sooner the water s examined after collection the more reliable are the results obtained.)THE ANALYST. 17 MEDIA TO BE EMPLOYED FOR ENURIERATION. The choice of medium lies between distilled-water gelatin, nutrient gelatin, distilled-water agar, gelatin agar, and nutrient agar. The reaction of the medium is of importance. For enumeration at room temperature any of these media may be employed, but for enumeration at blood heat an agar or gelatin agar must be used. The Americans seem to be using an agar medium only, and although on the ground of simplicity it might be desiqble to use a, single medium for enumeration under all circumstances--e.g., a distilled-water agar-it is felt by the committee that gelatin media frequently give indications of value that are lacking with agar-viz., liquefaction of the medium by many organisms and the more characteristic appearance of the colonies in it ; gelatin is therefore recommended. Since with I a polluted water (detection of pollution being the ultimate aim in water examination) nutrient gelatin gives a relatively larger number of colonies than distilled-water gelatin, nutrient gelatin should be used when one gelatin only is employed.At the same time, it is recognised that cultures in distilled-water gelatin compared with cultures in nutrient gelatin often give useful indications.Thus with an unpolluted water the number of colonies is usually relatively larger in distilled- water gelatin than in nutrient gelatin ; with a polluted water the converse is the case. Therefore the use of both gelatins (distilled-water and nutrient) is desirable, sets of plates being made with each medium. Similarly, it was felt by many members of the committee that a comparison of the ratio of the number of organisms developing at room temperature to those developing at blood heat gives useful indications. With EL pure water this ratio is generally considerably higher than 10 to 1, with a polluted water this ratio is approached, and frequently becomes 10 to 2, 10 to 3, or even less. The actual number of organisms growing at blood heat is also of considerable value apart from any question of ratio.Therefore it is suggested that plates of nutrient agar should also be employed and incubated at blood heat. Thus with surface waters, especially in tropical countries (as pointed out by Major Horrocks), varieties of the Bacillus JEuorescens liquefaciens and n o w liqaiefaciens and Bacillz~s liquefaciens may be abundant, and grow well at blood heat. In certain instances it is true that this ratio may be unreliable. PREPARATION AND REACTION OF MEDIA FOR ENUMERATION. (a) Distilled- Water Gelatin.-Ten per cent. gelatin in distilled water, and brought to a reaction of + 10 (Eyre’s scale). ( b ) Nutrient Gelatin.-Ten per cent. nutrient gelatin, preferably made with meat (beef) infusion and Witte’s peptone, and brought to a reaction of + 10 (Eyre’s scale).I n hot weather it may be necessary to increase the percentage of gelatin. Some members of the committee advocate the use of meat extracts in place of meat infusion, on the score of convenience and uniformity of composition, Brand’s Essence or Bovril’s Essence of Meat being recommended as the best. It is the general opinion, however, that Liebig’s Extract is less suitable for this purpose.18 THE ANALYST. ( c ) For enumeration at blood heat it is recommended that mtrie7zt agar should be employed, being prepared with the same constituents as nutrient gelatin, but substituting 14 per cent. of powdered agar for the gelatin. Reaction + 10. (d) Distilled- Water Agar.-Powdered agar 14 per cent., dissolved in distilled water, and brought to a reaction of + 10.Owing to the changes which occur in the reaction of the medium on keeping, the media employed should preferably be not more than three weeks old. AMOUNTS TO BE PLATED, SIZE OF DISHES, ETC. GeZatiiz.-For an ordinary water amounts of 0.2, 0.3, and 0.5 C.C. may be plated in Petri dishes of not less than 10 centimetres diameter, preferably done in duplicate. Bg~i*.-Two plates may be made with 0.1 and 1.0 c.c., and are preferably duplicated. I n dealing with an unknown water, and in all cases of doubt, additional sets of plates should be prepared with a dilution of the water (made with sterilized tap- water) of ten or hundred fold, according to circumstances. The amount of the medium in a plate should be 10 C.C.The sample must be thoroughly shaken and mixed in all cases before plating. TEMPERATURE OF INCUBATION. ( a ) Room temperature = 18-22' C. ( b ) Blood heat = 36-38" C. COUNTING. Counting to be done with the naked eye, preferably in daylight, any doubtful colony being determined with the aid of a lens or low-power objective. Time of Coz~m5zg.-Gelatin plates should be counted at the end of seventy-two hours ; but in all cases the plates should be inspected daily, in order that the count may be made earlier should liquefaction render this necessary. The blood-heat agar plates should be counted at the end of forty to forty-eight hours. SEARCH FOR BACILLUS COLI. ( a ) The glucose-formate broth method of Pakes. ( b ) The bile-salt broth method of McConkey.J f e t hod. -The committee recommend either- Incubation anaerobically at 42" C. increases the chances of success with either I t has also been suggested that the neutral-red (Griibler's) glucose broth medium The committee do not regard with favour the Parietti method, or the use of medium, and is strongly recommended. may be employed. carbolic acid media. QUANTITY OF WATER TO BE EXAMINED. As a routine 50 C.C. should be the minimal quantity examined for the presence of the BaciZZzLs coEi, quantities from a minimum of 0.1 C.C. to a maximum of 25 C.C. being added to the tubes of culture media.THE ANALYST. 19 The committee are of opinion that it is preferable to add the water directly t o the tubes of culture media, even with the larger amounts, rather than first to con- centrate by filtration through a porcelain filter (the filter brushing method).The culture media recommended may be diluted with at least an equal volume of the water without interfering with their cultural properties, and large tubes or small flasks may be used for the larger amounts. I n the case of the bile-salt lactose peptone water, the medium may for the larger amounts be prepared of double strength, ISOLATION OF BACILLUS COLI, IF PRESENT. If indications of the presence of the Bacillus coli be obtained in the preliminary This may be done by making surface cultures on plates of either- cultivations, the organism must be isolated and identified. (a) litmus lactose agar, reaction + 10 ; ( b ) bile-salt agar ; (c) nutrose agar of Conradi and Drigalski ; or ( d ) ordinary nutrient gelatin.The best medium of all is, probably, the nutrose agar of Conradi and Drigalski. Agar media have the advantage of saving time. IDEKTIFICATIOK OF, AND TESTS FOR, THE BACILLUS COLI. Having obtained coli-like colonies on the plates made from the preliminary cultivations of the water, sub-cultures must be made in order to identify the organism. The following, at least, should be made : The abundant growth so obtained enables many (a) Surface agar at 37" C. ( b ) Stab and surface cultures in gelatin. (c) Litmus milk incubated at 37" C. (d) Glucose litmus medium. (e) Lactose litmus medium. (f) Peptone water for indol reaction. sub-cultures and preparations to be made if required. This may be done in the same tube. CHARACTERS OF THE BACILLUS COLI.The Bacilhs coli is a small motile, non-sporing bacillus, growing at 37" C. as well as at room temperature. The motility is well observed in a young culture in a fluid glucose medium. It is decolorized by Gram's method of staining. It never liquefies gelatin, and the gelatin cultures should be kept for at least ten days in order to exclude a liquefying bacillus. It forms smooth, thin surface growths and colonies on gelatin, not corrugated, growing well to the bottom of the stab (facultative anaerobe). It produces permanent acidity in milk, which is curdled within seven days at 37" C. I t ferments glucose and lactose, with the production both of acid and of gas. The typical Bacillus coli must conform to the above description and tests. It generally also forms indol (best obtained in peptone-water cultures), gives20 THE ANALYST. a thick yellowish-brown growth on potato (greatly dependent on the character of the potato), sometimes (about 50 per cent.) ferments saccharose, changes neutral red (Grubler’s), and reduces nitrates, and half the gas produced by it from glucose is absorbable by KOH ; and these tests, if time and opportunity permit, may be performed in addition to the foregoing.The committee recognise that atypical BaciZZi coZi are met with, but in the present state of our knowledge hesitate to make any suggestion with regard to their significance. STREPTOCOCCI. The committee consider that it is a distinct advantage to search for streptococci. They may be looked for by making hanging-drop preparations of bhe fluid media employed for the preliminary cultivation of the Bacillus coZi (glucose-formate broth, etc.).The presence or absence of streptococci in these tubes gives also a quantitative value to the examination, just as in the case of Bacillus coli, and the result obtained should be stated. The streptococci should be isolated (best carried out on nutrose- agar plates), and their characters determined. BACILLUS ENTERITIDIS SPOROGENES. As already stated, the committee do not consider that it is essential as a routine procedure to search for the BuciZZus enteritidis sporogerzes, though in certain instances it may be of advantage to do so. A negative result in such cases is probably of more value than a positive one. This report is the outcome of prolonged deliberations, and every point has been carefully considered and discussed by the members of the committee. I n conclusion, the committee suggest that if the above recommendations were to be adopted by all engaged in the bacteriological examination of water it would conduce to uniformity of results, and would render comparable the data obtained by different observers. An addendum might be added to a report on an analysis conducted on these lines to the effect that the analysis had been carried out in conformity with the procedures recommended by the committee of The Royal Institute of Public Health, 1904. The committee beg to acknowledge their great indebtedness to Professor R. Tanner Hewlett, M.D., D.P.H., upon whom the great burden of the work of the committee has devolved. RUBERT BOYCE, M.B., F.R.S., Chairman. R. TANNER HEWLETT, M.D., M.R.C. P., Hon. Secre f n r y .

ISSN:0003-2654    

DOI:10.1039/AN9053000016

出版商:RSC    

年代:1905

数据来源: RSC

摘要:

THE ANALYST, 21 ABSTRACTS OF PAPERS PUBLISHED IN OTHER JOURNALS. FOODS AND DRUGS ANALYSIS. The Treatment of Frying Oils. F. Jean. (Rew. Gkn. Chim. pzwe et appl., 1904, vii., 326; through Chena. Zeit. Rep., 1904, xxiv., 291.)-The author has investigated the cause of frothing of vegetable oils used in cooking, and finds that : (a) When the oil is heated to 230" C., the volatile constituents are driven off and the property of "frothing" is lost, while the acidity is reduced. ( B ) When steam-distilled at 150°, the oil froths considerably and an acid distillate is obtained ; at 190"-225", the frothing is reduced and solid particles are carried over ; while above 225" the acidity increases. The distillate was found to contain ally1 sulphide, aldehydes, and fatty acids. (c) When heated with various fruits to 170°, and a current of air passed through the liquid, there was no frothing.H. A. T. The Determination of Fat in Flesh or Meats by Gerber's Acido-Butyro- meter. Toyokichi Kita. (Arch. Hyg., 1904, li., 165; through Chena. Zeit. Rep., 1904, xxiv., 291.)-Gerber's process is perfectly applicable to the determination of fat in meats, etc. After very thorough mincing, the meat is dissolved, and the fat liberated by warming and shaking in the butyrometer with a mixture of equal volumes of water and sulphuric acid (specific gravity 1.820-1.825) ; amyl alcohol and sulphuric acid are added in the usual way, and the percentage of fat read off after centrifuging for three to five minutes. H. A. T. The Flash Point or Ignition Temperature of Wine as an Index of the Alcohol Contents.P. N. Raikow and P. Schtarbanow. (Chenz. Zeit., 1904, lxxvi., 886.)-In former communications (Chem. Zeit., 1899, xxiii., 145 ; 1902, xxvi., 437) the authors describe a process for the determination of alcohol in aqueous solution by the flash point or temperature of ignition of the vapour. Abel's apparatus was used, and it was shown that the flash point was governed entirely by the amount of alcohol present ; and from a series of experiments reliable tables were drawn up. I n applying this method to wines it was found that the presence of certain volatile conipounds (as aldehydes, ethers, esters, etc.) sensibly reduced the observed flash point, giving figures indicating larger quantities of alcohol than were actually present.More satisfactory values were obtained by diluting the wine before the determination of the flash point ; but as at least 4 per cent. of alcohol is necessary before ignition of the vapour is possible, dilution cannot be carried to any great extent. H. A. T. The Detection of Saccharin in Wines, etc. Villiers, Magnier de la Source, Rocques, and Fayolle. (Am. de Chim. anal., 1904, ix., 418-420.)-The liquid is freed from alcohol by distillation and treated with an excess of neutral lead acetate in a slightly acid solution. The excess of lead is removed by precipitation with sulphuric acid, and the acid filtrate extracted with three successive portions of crystallizable benzene, the amount used each time being equal to half the volume of22 THE ANALYST. the filtrate.The benzene extract is partially distilled and tested for salicylic acid with a 0.1 per cent. solution of ferric chloride. The distillation is then completed without separating the ferric salt. The aqueous solution in the flask is now treated with 10 C.C. of dilute sulphuric acid (1 : 10) and heated on the water-bath, a warm saturated solution of potassium permanganate being added little by little until the liquid becomes pink. It is next extracted three times with half its volume of benzene, and the combined extracts evaporated on the water-bath. The residue is taken up with 2 C.C. of hot water, and a drop of the solution tasted. If the characteristic intense sweetness be observed, the remainder of the liquid is mixed with 2 C.C. of dilute sodium hydroxide solution (1 part of a solution of 36" with 10 of water) and rapidly evaporated to dryness.The residue is heated for three minutes in a tube immersed in a metal bath kept at 270" C., and then dissolved in dilute sulphuric acid (1 : 10). The solution is shaken with benzene and the extract shaken with 5 C.C. of a 0.1 per cent. solution of ferric chloride. The violet coloration characteristic of salicylic acid confirms the presence of saccharin in the original liquid. C. A. M. Commercial Substitutes for Pepper. F. Jean. (Ann. de Chiw. am& 1904, ix., 423-425.)-Two powders closely resembling black and white pepper are sold in France under the respective names of Le Gyifon and Le Mito. These are stated to consist of the vetch, popularly known as '( Chhe aux pigeo?zs," and are thus very similar to the pepper substitute sold as Erviop (ANALYST, xxix., 309).An analysis of Le Grifon gave the following results : Nitrogenous organic matter, 17.62 ; fat, 4-16 ; extractive matters, 62.77 ; ash, 3.05 ; and moisture, 12.40 per cent. C. A. M. The Constituents of Celery. M. Bamberger and A. Landsiedl. (Jfonuts- heft. f. Chem., 1904, xxv., 1030-1034.)-The root-stalks of fresh plants were found to contain mannite, asparagine, and tyrosine, but the authors could not detect leucine. The amount of asparagine isolated from different samples was fairly constant, 62 grammes yielding about 0.3 gramme, but the proportion of tyrosine was very small. C. A. M. The Chemical Composition and Formula of Adrenaline. G. Bertrand. (BUZZ. SOC. Chim., 1904, xxxi., 1188-1193.)-The material used in the author's investi- gations was extracted from the suprarenal glands of a horse, of which 118 kilos yielded about 125 grammes of crystalline adrenaline. A definite quantity of the alkaloid (110 grammes) was dissolved in 600 C.C. of normal sulphuric acid, and fractionally precipitated by means of ammonia, each of the precipitates being washed with water and alcohol and dried in vacuo. The seven fractions thus obtained were found to have the same elementary composition : Carbon, 58.46 - 58-83 per cent.; hydrogen, 7.19 - 7.30 per cent. ; and nitrogen, 7-66 - 7.74 per cent. From this the author concludes that adrenaline is a simple substance and not a mixture, and that its formula is Cl,,Hl,NO,, as found by Aldrich. C.A. M. The Determination of Antipyrin. P. Lemaire. (BzdZ. SOC. Phumz. Bar- deazix, 1904, 225; Ann. de Chinz. anal., 1904, ix., 433-435.)-The method is based onTHE ANALYST. 23 the fact that antipyrin combines with picric acid (1 mol. : 1 mol.), forming an almost insoluble crystalline compound. As the precipitate is slightly soluble or dissociates in water, it is necessary to have an excess of picric acid in the solution. The standard solutions required are a gC solution of sodium hydroxide and a $;- solution of picric acid (11.45 grammes per litre), standardized by titration with the sodium hydroxide solution, with phenol-phthalein as indicator. I n the determination 5 C.C. of a 5 per cent. solution of the antipyrin are mixed with 50 C.C. of the standard picric acid solution, which is added little by little with constant shaking. The liquid is then filtered, and 25 C.C. of the filtrate titrated with the standard alkali solution, phenol-phthalein being used as indicator. If n C.C. be required, the proportion of antipyrin is obtained by the formula (50 - 'EZ x 4.4) x 0.0094, and the result multiplied by 4 gives the amount in 1 gramme of the substance under examination. The crystalline precipitate can then be crystallized and dried, and its melting- point taken in order to determine whether it contains Lederer's iso-antipyrin, which has the same chemical characteristics and melting-point as Knorr's antipyrin, but is poisonous. The difference in the melting-points of the respective picrates affords a means of distinguishing between the two, the picrate of iso-antipyrin melting a t 168" C., whilst that of true antipyrin melts at 187" C. A colorimetric method can also be used in the determination, the filtrate from the insoluble compound being compared with solutions of picric acid of known strength. C. A. M.

ISSN:0003-2654    

DOI:10.1039/AN9053000021

出版商:RSC    

年代:1905

数据来源: RSC

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THE ANALYST. 23 ORGANIC ANALYSIS. The Estimation of Benzene Vapour in Coal Gas. Otto Pfeiffer. (Chenz. Zeit., 1904, lxxvi., 884.)-Harbeck and Lunge’s method for the determination of benzene in coal gas, which depends on the passage of the gas through a mixture of nitric and sulphuric acids with consequent nitration of the benzene and separation of this as di-nitrobenzene, is unnecessarily complicated. The gas is only measured after passing the acids, which necessitates special determinations of CO, and of the heavy hydro-carbons. I n the author’s modification the whole reaction is conducted in one piece of apparatus, and the di-nitrobenzene is titrated with stannous chloride. A 500 C.C. separating funnel, of accurately known capacity, is filled with the gas to be examined. The funnel is inverted, and 2 C.C.of mixed sulphuric and nitric acids (equal volumes of concentrated H,SO, and fuming HNO,) are introduced into the outlet tube, and carefully run into the separating funnel. The acids are distributed as much as possible over the inner surface, and the funnel allowed to stand. After half an hour 30 C.C. of concentrated soda solution are introduced in the usual manner, and the funnel shaken until the vapour formed disappears. If still acid the solution is neutralized with soda, and again rendered just acid with HCI, the nitro-compound extracted by repeated shaking with small quantities of ether, and the ethereal solution brought into a small flask with 1 grammeof dry potash and about 3 gramme of animal (blood) charcoal. After shaking the solution is filtered into a 200 C.C.flask, washed with ether, and this entirely driven off on the water-bath. About 10 C.C. of ctlcohol and exactly 10 C.C. of stannous chloride solution (150 grammes tin24 THE ANALYST. dissolved in hydrochloric acid + 50 C.C. HCl made up to 1,000 C.C. with water) are added, and the flask heated on the water bath for ten minutes. The solution is then made up to the 200 C.C. mark, and 20 C.C. are titrated with & iodine, using starch as indicator. The reaction between the stannous chloride and the di-nitrobenzene takes place according to the equation : C6H,(No2), + 6SnC1, + 12HC1= C6H,(NH,), + 6SnC1, + 4H,O. A blank experiment is made by heating 10 C.C. of stannous chloride solution with alcohol, diluting to 200 c c., and titrating 20 C.C.of this as above. H. A. T. The Composition of Borneo Tallow. J. Klimont. (Monatsheft. f. Chew%. , 1904, xxv., 929-932.)-This fat is obtained from the fruit of different varieties of dipterocarpus. The specimen examined by the author was a hard, yellowish-green fat, and gave the following analytical results : Acid value, 15.8 ; saponification value, 194.6; iodine value, 30-1; and melting-point, 34.5" to 35-7" C. It was found to contain tristearin with (probably) tripalmitin and at least two mixed glycerides. By repeated recrystallization of the fat (after removal of free fatty acid) from acetone crystals with the double melting-points 44" C. and 37" C. were obtained, and the elementary analysis and saponification and iodine values of these showed them to consist of oleo-distearin, C,H,.( C,sH330,).( C,8H,,0,)2.Another fraction yielded oleo- dipalmitin, C,H,.(C,sH3302)(C,6H,,0,),, melting at 33" to 34" C., and at 28" to 29" C. after being once melted. C. A. M. Investigation of the Colour Reactions of Wood Fibre. V. Grafe. (zonatshef't. f. Chem., 1904, xxv., 987-1029.)-The yellow coloration given by woody fibre with aniline salts, the red coloration with phloroglucinol and hydrochloric acid, and colorations given with other phenols are grouped by the author under the term of " Wiesner's reactions," and attributed to the action of certain constituents in the wood fibre upon these respective substances, while the hydrochloric acid only plays the part of accelerating agent. From his experiments (described in detail) he concludes that wood fibre contains several constituents, the principal being vanillin, methyl-furfural, and pyrocatechol, together with coniferin partly in the free state and partly combined with the cellulose as an ester and in the resin. The blue coloration given by wood fibre in the test with phenol, hydrochloric acid, and potassium chlorate is to be attributed to the coniferin, while the green coloration with concentrated hydrochloric or hydrobromic acid is most probably due to the methyl-furfural in conjunction with the coniferin.I n the author's opinion, Wiesner's reactions cannot be regarded as certain tests of lignification, since it is possible to prepare pyrocatechol and methyl-furfural in a simple way from cellulose, whilst the vanillin in the ligneous membrane may have had a similar origin.Maule's reaction, which consists in treating chips of wood for five minutes with potassium perman- ganate solution (1 per cent.), washing them with water, immersing them in hydro- chloric acid to remove the manganese dioxide, and finally exposing them to ammonia fumes (reddish-brown coloration), is also to be attributed to the presence of the Same constituents that produce Wiesner's reactions. C. A. M.THE ANALYST. 25 A New Reagent for the Detection of Blood Colouring Matters and their Decomposition Products. E. Riegler. (Zeit. anal. C/zem., 1904, xlii., 539-544.)- The method is based upon the formation of an alkaline alcoholic solution of hEmochromogen, which has a, brilliant purple red colour, and shows with great clearness the two characteristic absorption bands in the spectrum. The reagent is prepared by shaking a solution of 10 grammes of sodium hydroxide in 100 C.C. of water with 5 grammes of hydrazine sulphate until the latter dissolves, and then adding 100 C.C. of 96 to 97 per cent. alcohol. The liquid is well shaken, allowed to stand for two hours, and filtered. The filtrate gives the same htwnochrornogen reaction with blood, oxyhEmoglobin, haemoglobin, methzmoglobin, or haematin. Thus, on shaking 0.05 gramme of commercial hmnoglobin or 0.5 C.C. of blood with 30 C.C. of the reagent, the characteristic coloration is obtained. In testing liquids such as urine for blood 10 C.C. are shaken with 10 C.C. of the reagent, and the whole allowed to stand for thirty minutes. For the detection of blood stains on linen, a small fragment of the material is moistened with 3 or 4 drops of the reagent, and examined under the microscope, and eventually with the microspectroscope. C. A. M.

ISSN:0003-2654    

DOI:10.1039/AN9053000023

出版商:RSC    

年代:1905

数据来源: RSC

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THE ANALYST. 25 INORGANIC ANALYSIS. Electrolytic Determination of Bismuth. A. Hollard and L. Bertiaux. (Bull. SOC. Chirn. 1904 xxxi. 1131-1133.)-Separation of Bismith und Copper.-The solution of the two metals in the form of sulphates (which should not contain a large excess of sulphuric acid) is brought to the boiling-point and treated with a large excess of phosphoric acid. After standing overnight the precipitate is collected and washed with dilute phosphoric acid (1 part of specific gravity 1.711 with 19 parts of water) and then with ammonium hydrosulphide and potassium cyanide solution to remove the copper. This washing solution ought to contain in 100 C.C. 5 grammes of potassium cyanide and 5 C.C. of ammonium hydrosulphide obtained by saturating a 10 per cent. solution of ammonia with hydrogen sulphide.The precipitate of bismuth phosphate is dissolved in dilute nitric acid (I l ) and the solution evaporated with 12 C.C. of sulphuric acid until abundant white fumes appear when the bismuth will have been converted into pyrophosphate. The residue is then diluted to 300 c.c. and the liquid electrolysed for twenty-four hours with a current of 0.1 ampere per square decimetre. (No other details given.) The bismuth deposited should be tested with ammonia for copper which if found should be determined colorimetricall y. Separation of Binmth and Lead-The separation of lead from bismuth in the form of sulphates is not accurate when the proportion of lead is large owing to the lead sulphate retaining a considerable amount of bismuth; whilst if a solution of bismuth in sulphuric acid containing insoluble lead sulphate be electrolysed an appreciable quantity of lead is deposited with the bismuth.This difficulty is obviated as follows The solution containing the two metals in the form of nitrates is evaporated with an excess of 12 C.C. more than the amount of sulphuric acid required to combine with the bismuth and lead present. As soon as abundant white fumes appear the liquid is cooled diluted to 300 c.c. mixed with 35 C.C. of absolute alcohol and electrolysed for forty-eight hours with a current of 0.1 ampere. Th 26 THE ANALYST. addition of the alcohol renders the lead sulphate completely insoluble without interfering with the deposition of the bismuth. The results quoted show that minute quantities of bismuth can be accurately separated from large amounts of lead by this method.C. A. M. Analysis of Commercial Tin and its Alloys. A. Hollard and L. Bertiaux. (BzdZ. SOC. Chim. 1904 xxxi. 1128-1131.)-Arsenic.-Five grammes of the tin are placed in an apparatus for distillation of the arsenic and treated with a solution of 50 grammes of ferric sulphate in 150 C.C. of hydrochloric acid and the arsenious chloride determined volurnetrically (ANALYST xxv. 301). Lead Bismuth and 1ropz.-Five grammes of the tin are dissolved in hydrochloric acid with the addition of the smallest possible quantity of nitric acid. Ammonia is then added in excess after which a current of hydrogen sulphide is introduced until the whole of the tin has dissolved. The solution is filtered from the sulphides of lead iron and bismuth and the part of the copper sulphide that has not been dissolved by the ammonium sulphide.The precipitate is washed with water and then with a solution of hydrogen sulphide and redissolved in hydrochloric acid con-taining bromine. The excess of bromine is expelled by heat and the liquid treated with hydrogen sulphide which precipitates the lead bismuth copper and the small amount of tin which was precipitated with them. This precipitate is collected and washed with a solution of hydrogen sulphide. The iron left in the solution is precipitated with ammonia after the liquid has been boiled and treated with nitric acid. The precipitate is redissolved in hydro-chloric acid reprecipitated with ammonia and the iron determined volumetrically by converting it into ferric chloride nearly neutralizing the solution with sodium bicarbonate mixing it with 5 C.C.of carbon bisulphide and an excess of a concentrated solution of potassium iodide and leaving it in the closed flask for thirty minutes, after which the liberated iodine is titrated with standard sodium thiosulphate solution-Fe2C1 + 2KI = 2FeC1 + 2KC1+ 21. The precipitate of sulphides is dissolved in hot hydrochloric acid containing bromine, solution being completed by washing with hot water. The liquid is mixed with ammonia in excess and a little potassium cyanide (to keep the copper in solution), and treated with a current of hydrogen sulphide which now precipitates only the lead and bismuth. The precipitate is collected washed with dilute ammonium hydrosulphide then with water and then with a solution of hydrogen sulphide.The sulphides are converted into sulphates by being dissolved in nitric acid contain-ing bromine and evaporation with sulphuric acid. The lead sulphate is filtered off and determined electrolytically (BuZl. SOC. Chim. xxxi. 239) whilst the bismuth is determined electrolytically in the filtrate (Conzptes Rendus 1904 366). AntZmoizy.-One gramme of the original tin is treated with aqua regia and the nitric acid subsequently expelled by repeated evaporation with hydrochloric acid. The dry residue is rendered alkaline by the addition of several drops of sodium hydroxide solution and taken up with a mixture of 200 C.C. of concentrated sodium hydrosulphide solution and 40 C.C.of a 20 per cent. solution of potassium cyanide, and electrolysed with a current of 0.1 ampere only the antimony being deposited (ANALYST xxviii. 228) THE ANALYST. 27 Copper. % 0.480 0.000 0.040 0.030 -- _ Copper and Sulphur.-Five grammes of the tin are treated with nitric acid and the mixture evaporated to dryness on the water-bath. The residue is taken up with water acidified with nitric acid the liquid decanted and the residue washed with the same acidified water. The copper in the filtrate and washings is separated and determined by electrolysis. The sulphur in the solution is determined by evaporating the liquid on the water-bath taking up the dry residue with water filtering the solution adding a few drops of hydrochloric acid and precipitating the sulphate with barium chloride.Compositioyz of Commercial Samples.-The following results were thus obtained : Arsenic. --% 0.079 0.022 0-034 0-118 0.033 Commercial Tin. Zinc. % -- German . . .,. Swiss . . . Commercial sample . . . Chinese . . . Malaccan . . . - -~ - _ _ Lead. -% 0.498 -Anti-mony. % 0-545 1.174 0.110 0-044 -Nickel I and 1 Iron. Cobalt. i % I % l -I --0.0281 0.040 - I 0.037 0-014 I 0.009 -Bis-muth. % 0.060 0.580 --I Alloys of Tin a d Lead (Solders etc.).-One gramme of the finely-divided alloy is mixed with 10 grammes of copper and treated with 52 C.C. of nitric acid in a 350 C.C. beaker. The nitric acid used is diluted with a little water the amount of which is smaller in proportion to the quantity of tin present.The liquid in the beaker is diluted to 300 c.c. and heated on the water-bath for a short time to make the oxide of tin collect at the bottom after which it is cooled and the lead separated electro-lytically in the form of peroxide (Bull. Xoc. Clzim. 1904 293). The spiral immersed in the liquid ought to reach nearly to the bottom of the flask. Under these con-ditions the oxide of tin does not interfere with the separation of the lead. C. A. M. An Improvement on Drown and Shimer’s Methods of determining Silicon in Iron. J. Thill. (Zeit. anaZ. Chem. 1904 xliii. 552 553.)-An objection to these methods is the long time required for the evaporation of acids used whilst if a naked flame be used instead of the water-bath for heating there is danger of loss.The following modification is stated to give accurate results within an hour. From 1 to 2 grammes of the powdered crude iron (according to the amount of silicon) are placed in a beaker holding 400 to 500 c.c. and treated with 50 to 70 C.C. of a solution prepared as follows A litre of concentrated sulphuric acid is diluted with an equal volume of water and mixed with a litre of nitric acid (specific gravity 1.40) and a solution of 240 grammes of ammonium chloride in a litre of water. After adding the required amount of this reagent to the iron the liquid is heated to dissolve the iron and evaporated on wire gauze over a Bunsen flame until white fumes appear. The residue is then diluted with about 100 C.C.of water and heated until the sulphates have con~pletely dissolved after which the liquid is filtered and the insoluble residue washed with hot water then with 10. C.C. of hot dilute hydro-chloric acid and again with hot water. Finally the filter and its contents are ignited while still moist then heated in a muffle and weighed. C. A. M 28 THE ANALYST. The Colorimetric Determination of Carbon in Steel. H. C. Boynton and H. K. (Xtahl und Eiserz 1904 1070 ; through Cltem. Zeit. Rep 1904 xxiii. 283.)-The condition of the carbon in steel determines the amount of colour produced in Eggertz process. Three samples were taken of a piece of steel containing 0.48 per cent. of carbon, and heated to 1200O C. The first was cooled rapidly in an air blast the second was allowed to cool spontaneously in the air while the third was left in the furnace and cooled very gradually.The analysis of the blast-cooled sample showed only 0.34-0-35 per cent. of carbon that of the air-cooled sample 0.36-0-39 per cent. while the sample cooled in the furnace gave the full (0.48 per cent.) amount. H. A. T. APPARATUS. Note on the Durability of Platinum Crucibles. G. Siebert. (Chewz. Zeit., 1904 lxxiv. 869.)-The author who is a member of Messrs. G. Siebert’s Platinum Works Hanau considers that the occasional rapid deterioration and fracture of platinum crucibles etc. is not always due to the presence of chemical impurities, such as iridium but rather to the physical properties of the platinum. H e finds that when proper precautions are taken to obtain the highest possible degree of homogeneity in the platinum in all stages of manufacture the crucibles are practically indestructible.Where however such precautions are not taken though they may be made with pure metal deterioration is very rapid in the articles. H. A. T. OBITUARY NOTICE. THOMAS A. POOLEY B.Sc. F.I.C. WE regret to record the death after a prolonged illness of Mr. Thomas A. Pooleg, B.Sc. F.I.C. for many years Public Analyst for the County of Essex and the Borough of West Hem and an old member of the Society. Mr. Pooley who was sixty-three years of age at the time of his death was educated first in France and subsequently at University College and King’s College London. He took an honours science degree st London University in 1864 with special distinction in chemistry. For a number of years he directed his attention chiefly to the chemistry of brewing, being for a time Editor of the Brewers’ Guardian and for a number of years a regular contributor to the Bmzoers’ Journal. During the later part of his life he devoted himself chiefly to food analysis in connection with the duties of his public appoint-ments already referred to. He rarely attended the meetings of the Society and was therefore personally unknown to very many of his colleagues but by the few who knew him his kind a d genial friendship was much prized PLATES TO ILLUSTRAT

ISSN:0003-2654    

DOI:10.1039/AN9053000025

出版商:RSC    

年代:1905

数据来源: RSC