摘要:

The Faraday Society is not responsible for ofiinions expressed before it by Authors or Speakers. Strength in Grammes of After per Litre. Days. available Chlorine At Start. 31 - Dark Amber Bottle ... 4.216 4.180 Light Amber Bottle ... 4.216 4.145 ---- cransacttons; After After After 212 689 750 Dajs. Days. Days. _ _ _ ~ _ _ _ _ _ _ ~ 4.~53 3,258 3.224 3.826 2.551 2.480 OF After 1,358 Days. 2.657 1.771 FOUNDED 1903. After 1,817 Days. ___ 2.515 1275 TO PROMOTE THE STUDY OF ELECTROCHEMISTRY, ELECTROMETALLURaYp CHEMICAL PHYSICS, METALLOGRAPHY, AND KINDRED SUWECTS. VOL. IT. FEBRUARY, 1907. PART 3. SOME INVESTIGATIONS RELATIVE TO T H E DEPRECIA- TION OF ELECTROLYTICALLY PRODUCED SOLU- TIONS OF SODIUM HYPOCHLORITE. By W. POLLARD DIGBY, A.M.I.E.E. ( A Paper rend bcfore the Fnraday Society 092 Tuesday, November 13, 1906, DR.F. MOLLWO PERKIN, TREASURER, in the Chair.) In a previous Paper read before the Faraday Society the writer alluded to the effect of instability on the efficiency of hypochlorite production, and cited, in one instance, depreciations of 0'20 to 0.45 grammes per litre in six hours, and in another instance of from 0.03 to 0.40 grammes per litre during a period of twelve hours. These depreciations referred only to the reaction or reversion to sodium chloride taking place during the process of manufacture, but did not concern solutions made under circumstances calculated to maintain their strength for fairly long periods, nor did they concern con- ditions of storage likely to affect this stability. The present note, therefore, contains some records of depreciations taking place over a long period, and also some records taking place over a short period under exceptional conditions of storage.A.-GLASS BOTTLE TESTS. These tests cover, firstly, a comparison between the effect of storing hypochlorite solution in bottles of dark and light amber colour, the first and last dates being over five years apart. TABLE I. The initial strength in available chlorine being in each case 4216 grammes per litre, the final strength after 1,817 days had fallen to 2'515 grammes per litre with the dark amber bottle, and to 1.275 grammes per litre with the light166 DEPRECIATION OF ELECTROLYTICALLY PRODUCED Dark Amber Bottle ... ... Medium Amber Bottle ... White Glass Bottle ... ... Dark Blue Glass Bottle ...amber bottle, the average loss per diem in the first instance being practically 0'936 milligrammes, and in the second instance 1.6~9 milligrammes. A second set of bottle tests covering a lesser period gives results concern- ing the relative value of dark and medium amber bottles, and contrasts these with the results obtained from transparent white glass bottles and dark blue glass bottles, the initial strength in available chlorine being :- TABLE 11. 4.145 3-791 3-623 3-051 2.480 1'9x3 4.145 3.791 3.623 3.051 2.480 1.878 4.145 3.190 2.691 1.417 0.708 0.354 4.145 3.330 3.082 1.771 0.887 0'425 Strength in Grammes of available Chlorine per Litre. -- In each case initially 4.145 grammes per litre, the final strength after 1,187 days had fallen in the case of the dark amber bottles to 1.913 grammes per litre, in the case of the light amber bottles to 1,878 grammes per litre, in the case of the uncoloured glass to 0.354 grammes per litre, and in the case of the blue glass to 0.425 grammes per litre.The loss of available chlorine in milligrammes per day, therefore, works out as follows : Dark amber, 1-87 ; medium amber, 1-90 ; clear glass, 3-16 : blue glass, 3.~3. The above tests are set out in Diagram I. As regards the exposure of these bottles to the sunlight, an attempt was made to render the conditions as nearly as possible equal to those to which they would have been subjected in a chemist's shop. The bottles were placed on a shelf opposite a window facing due south, and received a full measure of sunlight, but practically no artificial light whatever.In order that every factor likely to bear upon the question might be available for future investigators of hypochlorite stability, the outside area of the bottles was measured, and the ratio of square centimetres of surface to cubic centi- metres of contents was as follows :- ... 0-0153 sq. cm. per cub. cm. of contents. Dark Amber Bottles Light Amber Bottles ] Clear Bottle ,.. ... ... 0'325 ,) 9 9 ,, Dark Blue Bottle ... ... 0'345 ,) ,, , t It is not, of course, any new discovery that the stability of hypochlorite solutions is affected prejudicially by sunlight. In regard to this, however, it must be pointed out that what takes place in dark amber bottles exposed to the light in the manner described, also takes place, but to a less degree, when the same bottles are placed in wooden boxes and nailed down.Deterioration due to light being eliminated, one can only blame the rubber stopper used- which contained a minimum of pure rubber-or the inherent instability of t h e substance of electrolytically produced hypochlorites. B.-SINGLE METAL TESTS. In the previous Paper it was pointed out that metallic impurities had a marked effect on the depreciation. The metallic fittings of the tanks were connected to the negative terminals of the generator, and therefore acted as subsidiary cathodes. When the plant was standing idle during the week-end, these would be liable to be attacked by the hypochlorite solution, and, forSOLUTIONS OF SODIUM HYPOCHLORITE 3 s * 3 8 t F P 8 8 t! z a 4 R - 8 a i 0 5 0 c t t t168 DEPRECIATION OF ELECTROLYTICALLY PRODUCED example, ferric chloride might be formed then ; or else from rust brought in with the water used to make up the electrolyte. In order to ascertain how far single metals placed in open earthenware jars in hypochlorite solutions were attacked and what depreciation resulted, strips of metal foil, and also of ebonite, having a gross area of IOO square centimetres, were each separately immersed in 900 cubic centimetres of hypochlorite solution of 3.887 grammes of available chlorine per litre strength, and tests were taken at the end of four, eight, and twenty days' immersion.TABLE 111. Time in Hours from Commencement. Graphite, Grammes av. C1. per Litre ... Copper, Do. ... Ebonite, Do. ... Zinc, Do.... ... Lead, Do. ... ... Iron, Do. ... ... Tin Plate, Do. ... g6 3'887 3'887 3.826 3.118 3'542 2.267 2.69 I I 92. __ ~- 3'887 3'887 3.580 2'0.55 I '560 o%jo 0.850 480. 3'887 3.614 3.401 0.92 I 0.636 0.283 0.142 Remarks. No change whatsoever. Very faint green deposit on plate. Depreciation of 0.273 grammes per litre. Depreciation 0.486 grammes per litre. Heavy white deposit on plate, solution milky. Depreciation 2.966 grammes per litre. Plate black. Depreciation 3.251 grammes per litre. Heavy dark rusty deposit. Depre- ciation 3'604grammes per litre. Heavy rusty deposit, light in colour. Depreciation 3.745 grammes per litre.SOLUTIONS OF SODIUM HYPOCHLORITE 169 In regard to the last line of the above table, pure tin from some neigh- houring engineering works was ordered, but the tinned plate of commerce supplied. As a result, in the early stages, while the coating remained intact, the tin-plate was superior to iron, but subsequently, owing to local galvanic action, the depreciation was more active, corresponding to that of the iron curve. With regard to the graphite used, it can only be observed that, while not a metal, it was included in this series in order to test the graphite for metallic impurities which might give rise to local action.That none occurred is a testimony to the purity of the material experimented with. C.-METAL COUPLE TESTS. A further series of tests was carried out in which, instead of using a single metal, two metals were used, as well as single metals and ebonite sheets. Twenty-onc sets were placed in open jars, the gross area of each metal in each unit being IOO sq.cm., and the volume of liquid 900 cub. cm. The initial strength in grainmes of available chlorine per litre was 3.826. The metals were joined together by short wires only a few centimetres in length, the wire used in each case being insulated throughout its length, and also at the joint, by Chatterton compound applied hot. For the purpose of comparison and discussion, diagrams Nos. 3 to 9 inclusive give the results of these tests under the headings of each metal. For instance, test No. 8 is to be found both under the Copper Series (Fig. 4), and under the Iron SeriesTABLE IV. Grammes available Chorine per Litrc. W v 0 U - -_-_ i Test No. - I 2 3 4 2 7 8 0 I 0 I1 I 2 I3 I4 I 5 16 I7 I8 I9 20 21 Description of Couple.Lead and copper with copper wire ... Lead and graphite with lead wire ... ... Lead and iron with lead wire ... ... Lead and tinned plate with lead wire ... Lead and zinc with lead wire ... ... Lead and ebonite with lead wire ... ... Copper and graphite with copper wire ... Copper and iron with copper wire ... ... Copper and tinned plate with copper wire Copper and zinc with copper wire ... ... Copper and ebonite with copper wire ... Graphite and iron with tin wire ... ... Graphite and tinned plate with tin wire . . . Graphite and zinc with zinc wire ... ... Graphite and ebonite with tin wire ... Iron and tinned plate with tin wire ... Iron and zinc with zinc wire ... .. Iron and ebonite with tin wire ... ... Tinned plate and zinc with zinc wire ...Tinned plate and ebonite with tin wire ... Zinc and ebonite with zinc wire ... ... At Start. 3'826 3'826 3'826 3'826 3.826 3'826 3'826 3'826 3'826 3'826 3'826 3'826 3.826 3.826 3.826 3.826 3.826 3.826 3-826 3 826 3-826 After 24 Hours. 3'744 3'684 2'SSI 2.692 1.841 3.826 3'542 2'7.51 2'19j 2.692 3.614 2.266 2.910 2'19.5 3'542 2.480 2.197 3.118 2.991 3.118 i.779 After 48 Hours. 3'542 3'472 1'842 2'338 0.708 3.614 3.401 1.417 1'175 1.134 3'614 1.417 1.771 1-17!? 3'465 1.204 0.780 2.194 1.346 2.409 2'551 After yj Hours. 3'407 3'649 * 1.204 1'913 2.692 2'444 1.063 0.283 0.3 54 3'474 0.63 8 092 I 0'354 3.401 0'2 I 2 0:738 0212 1.414 092 I 1'842 2,167 M G E; Condition of Plates at End of Test. ?i 8 2 2 No deposit, lead turning black. No deposit, lead turning black.Z Heavy deposit, light rusty colour on iron plate. Heavy deposit, light rusty colour on tinned plate. Heavy white deposit on zinc plate, solution milky. No appreciable deposit, lead turning black. Slight green deposit on copper. Heavy deposit, light rusty colour on iron plate. M r M td 0 Heavy deposit, light rusty colour on tinned plate. Heavy white deposit on zinc plate, solution milky. No deposit on copper plate. Heavy deposit, light rusty colour on iron plate. Heavy deposit, light rusty colour on tinned plate. Heavy white deposit on zinc plate, solution milky. { iron plates. Heavy white deposit on both plates, solution milky. Slight deposit, light rusty colour on iron plate. Heavy white deposit on zinc plate, solution milky. Slight deposit on tinned plate, light rusty colour.Slight white deposit on zinc plate, solution milky. Slight rusty deposit, light rusty colour on both plates. 2 r r Deposits of light rusty colour on both plates, heavy on 0 * 4 'd z 0 U c c1 M U - * Probable the previous titration (48 hours) gave too low a reading.SOLUTIONS OF SODIUM HYPOCHLORITE 171 (Fig. 6). This, while in some respects redundant, permits of easier com- parisons. Also in each diagram the curve for the single metal of the series is given for ninety-six hours. Taking these diagrams in their order, the Lead Series (Fig. 3) shows that the galvanic action is greatest in the case of the lead and zinc couple, next greatest in the case of lead and iron, while the lead-graphite, lead-copper, and lead-ebonite couples show a depreciation rather greater than that due to the lead plate alone.The Copper Series (Fig. 4) shows the greatest depreciation in the case of the copper-tinned plate couple, which agrees closely with the copper-zinc curve. The lead and copper couple stands out superior to the copper- graphite. The copper-ebonite couple gives a greater depreciation than either copper or ebonite alone. The Graphite Series (Fig. 5) is notable for the fact that the worst depreciations are due to couples of graphite-zinc, graphite-iron, and graphite- tinned plate, in the order named. The Iron Series (Fig. 6) show heavy depreciations, the worst being that due to the iron-tinned plate couple. Probably the 24-hour reading on the iron-ebonite couple is incorrect. The Tinned-plate Series (Fig.7) is somewhat irregular, perchance owing to irregularities in the local action on the surface of the tinned plate. The Zinc Series (Fig, 8) is also irregular. Table IV. shows what is difficult to depict on a small diagram, the final identical effect of the lead-172 DEPRECIATION OF ELECTROLYTICALLY PRODUCEDSOLUTIONS OF SODIUM HYPOCHLORITE I73 4‘00 0 3 coo 3 000 2 000 , 0 0 0 co 0 0 ‘OL. II-T7174 DEPRECIATION OF ELECTROLYTICALLY PRODUCED zinc couple with the iron-zinc couple, and of the copper-zinc couple with the graphite-zinc, The Ebofiite Series (Fig. 9) is, of course, not a metal couple test. It is not easy to explain why the depreciation should in each case exceed that for the single metal plate of identical area. D.-SINGLE METAL TESTS WITH INCREASED AREAS. The effect of varying the exposed area of the metal immersed in the solution was also studied.The volume of the liquid was c p cub. cm., tests being taken at 24-hour intervals for eight days. The results are set out in Table V. The general deductions from this set of experiments are that the amount of depreciation due to metallic contact and chemical reaction in any given time varies directly with the area of the exposed surface, for solutions of equal strength in available chlorine. Figs. 10, 11, and 12 show the results of varying the area for iron, zinc, and tin respectively. No curve has been plotted for copper, which does not seem to cause corrosion to any material degree when the area is doubled. The figures given in Table V.represent but little more than might have been anticipated from exposure to air and light.TABLE V. Grammes available Chlorine per Litre. Test No 22 23 24 25 26 27 28 29 30 31 32 33 34 35 Description, Metal and Exposed Area. Iron, 400 sq. cm. ... ,, 300 sq. cm. ... ,, 200 sq. cm. ... ,, IOO sq. cm. ... Zinc, 400 sq. cm. ... ,, 300 sq. cm. ... ,, 200 sq. cm. ... ,, IOO sq. cm. ... Tin, 400 sq. cm. ... ,, 300 sq. cm. ... ,, 200 sq. cm. *.. ,, IOO sq. cm. ... Copper, 200 sq. cm. ,, 100 sq. cm. ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... At Start. After 24 Hours. 1 '452 1.708 1'984 2'905 3'224 3'330 3.401 3'507 2'090 2.090 2.728 2.829 3'554 3'554 After 48 Hours. 0.425 0.466 I '063 2'05 5 2'691 2.691 3'224 3.401 1.240 1'559 2*090 2'303 3'507 3'554 After 72 Hours.0'0 I 0 0.017 0.8 15 2'055 2.480 2'480 3.082 3'334 0.885 1.134 1-878 2'196 3'452 3'554 After ~6 Hours. 0.006 0'010 0'425 1.842 1.842 2'055 2'657 3'153 0'673 0.885 "559 1.948 3'437 3'554 After 120 Hours. No trace No trace 0'354 1.557 1'523 1.880 2'480 2'940 0.463 0.638 1.418 1.842 3'437 3'507 After re, Hours. No trace No trace 0777 "'55 1.155 1'452 1.913 2.571 0'777 0'425 1.311 I -878 - 3.401 3 - 9 7 After 168 Hours. No trace No trace 0'010 I'OOO 0.850 1.240 1.842 2'409 O"77 0'354 1'204 1'55 3'354 3 '507 After 192 Hours. No trace No trace 0.007 0'779 0'674 1'027 "275 2'196 0'0 I0 0'212 I ,098 ,1*918 3'354 3'452176 DEPRECIATION OF ELECTROLYTICALLY PRODUCED E.-VALUE OF PROTECTIVE COATINGS.It has been shown above that if hypochlorite solutions are allowed to come into contact with single metals corrosion of the metal and depreciation of the available chlorine results. When two metals are present in electrical contact corrosion and depreciation are accentuated. A series of tests was therefore made with six metal couples and three single metals. Tests were taken every twenty-four hours for ten days. In each case goo cc. of hypo- chlorite solution containing 3.614 grammes of available chlorine per litre was used. A "biturnastic" paint was applied to each plate. The following figures summarise the results obtained :- TABLE VI. Test No. 36 38 37 39 40 41 42 43 44 Description of Metal (exposed Area 100 sq. cm. for each Plate). Lead and zinc . . . . . .Copper and zinc ... Lead and iron . . . . . . Iron and tinned plate ... Zinc and tinned plate ... Tin . . . . . . . . . Zinc . . . . . . . . . Copper . . . . . . . . . Iron . . . . . . . . . Final Strength at endof 240 Hours. 3'507 3.401 2.905 2'55 1 3'437 3'437 3'437 3'507 3.082 Actual Loss in Grammes during Period. 0'0963 0'9.567 0'1877 0.63 8 I 0' I 693 0' I 693 0.4788 0' I693 0.0963 Daily Per- centage Loss during Period. 3'17 19'34 27.86 4-62 4-62 4.62 3-17 14-72 5-89SOLUTIONS OF SODIUM HYPOCHLORITE = 77 The above results must be regarded as bearing upon the effectiveness of applications only. Best results, for instance, were obtained in these pro- tected metal tests from the lead-zinc couple, which, according to Table IV., test No. 5, should have been about the worst.As it is a matter of difficulty t o paint the inside of small plates, and, still more, of pipes evenly, the writer deprecates reliance upon insulating materials for the protection of any vessel in which hypochlorite liquids are stored, or of any metallic piping in contact with hypochlorite liquids. When once the paint breaks down, corrosion of the metal will follow at a rapid rate. Arising out of the above tests, it occurred to the writer that wood boiled in bitumen might be used as a substitute for slate electrolysing tanks, and perhaps as a substitute for ebonite in electrode construction. Messrs. Cal- lender’s Cable and Construction Company, Ltd., responded very promptly and courteously to a request for samples of wood which had been bitu- menised.These samples had 200 square centimetres of their surface (not including the edges) immersed in vessels containing three litres of liquid of a strength of 3.153 grammes available chlorine per litre. The woods tested were oak, elm, and ash, each of which had been submitted to three different temperatures, viz., No. I “ Low ” temperature ; No. 2 [‘ Medium ” tempera- ture ; and No. 3 “ High” temperature. The experiments were continued for fifteen days, titrations being made at the end of each twenty-four hours. The final results are given i n the following table, the interim depreciations being shown in Fig. 13 :-178 DEPRECIATION OF ELECTROLYTICALLY PRODUCED TABLE VII. Kind of Wood and Grade of Treatment. Ash No. I . . . . . . Ash No. 2 . . . . . . Ash No. 3 .. . . . . Elm No. I . . . . . . Elm No. z . . . . . . Elm No. 3 . . . . . . Oak No. I . . . . . . Oak No. 2 . . . . . . Oak No. 3 . . . . . . Final Strength of Solution in Grammes of available Chlorine. 1'524 0.92 I 0.8 I 5 1.204 0.815 0.8 I 5 I -807 1.138 0.389 Loss in Grammes of available Chlorine during Period. 1.629 2-232 1'949 2'338 2'338 2'338 1.346 2.015 2.761 Average Loss in Grammes of available Chlorine per Day throughout Period per 100 sq. cm. of Exposed Surface. 0.0543 0.0744 0.0779 0.0649 0.0779 0'0779 0.0448 0.0672 0'0921 These final results show that the No. I series (submitted to low tempera- tures) have given the best results throughout, and that the Oak No. 2 sample ranks after these. The Ash and Elm samples (Nos. 2 and 3 in each case) are practically identical, Oak No.3 coming last on the list. ExaminingSOLUTIONS OF SODIUM HYPOCHLORITE I79180 DEPRECIATION OF ELECTROLYTICALLY PRODUCED the individual curves in Diagram 13, it will be seen that except for the Elm samples distinctive differences only began to be apparent after the fourth day. The laboratory records state on that occasion that ‘( while it cannot be said that the hypochlorite solution has actually eaten off the ,bitumen, it has certainly changed it to a very light colour.” An examination of the samples of wood at the end of the test certainly shows that ultimately the bitumen was eaten off. From these tests it may be concluded that, while bitumenised wood resists disintegrating action while the coating is unimpaired, that coating has relatively a short life.It should not, therefore, be used in the construc- tion of electrodes, nor of electrolysing tanks ; but for temporary purposes it would be useful for the preservation of wooden troughing. It may be thought by some that this account of some instances of the depreciation of electrolytic hypochlorite solution contains too much of rela- tively irrelevant detail. But the author having given a good part of over ten years to the making of hypochlorite solutions, realises that success is only obtained by infinite attention to minute details, and has found much of the detail here given of infinite value in the practical working of such processes. As regards methods of manufacture, these have nothing to do with the present Paper, which is wholly concerned with certain causes which may contribute towards the unsatisfactory operation of an installation. Storage, transport and methods of conveyance from place to place, or even from one part of a factory to another, are details meriting attention. Certain con- ditions of storage may clearly be regarded as fatal to stability, particularly those in which the galvanic action of dissimilar metals is likely to arise. These tests were all made with a solution produced at the works of a com- pany in the north of England manufacturing electrolytic hypochlorites. While the relative order of values of different metals as occasioning depreciation is as stated, these figures must only be regarded as absolute in regard to the product of the factory in question. Tests with solutions produced by other processes, while agreeing in order of value with those recited, do not give identical analytical results, the rate of loss being accelerated (or retarded) according to method of manufacture. The discovery of this latter point has led the author to devise a galvanic couple test which, in a given time, for any solution, will indicate what may perhaps be called its I‘ stability coefficient.” Detailed tests are at present being carried out on various hypochlorite solu- tions, both chemical and electrolytic, with a view to simplifying the test methods. It is hoped that a Paper 011 this subject will be of interest to the Society. The writer desires to express his thanks to Mr. F. T. Talmadge for valuable assistance rendered in carrying out these tests.

ISSN:0014-7672    

DOI:10.1039/TF9070200165

出版商:RSC    

年代:1907

数据来源: RSC

摘要:

180 DEPRECIATION OF ELECTROLYTICALLY PRODUCED DISCUSSION. Dr. S. Rideal, referring to the author’s remarks regarding the stability of the solutions, said that this was an important factor when such solutions had to be kept for any length of time, but in the experiments that he had made the germicidal effect was required immediately after the solution was made. It was now well known that for effective sterilisation this reagent could only be employed when there was no readily oxidisable organic matterSOLUTIONS OF SODIUM HYPOCHLORITE 181 present-in fact, the amount of chlorine required for sterilisation could be determined from the oxygen consumed, as these two figures were pro- portional to one another. Dr. H. Borns agreed with Dr. Hutton that the theoryof the formation of hypochlorites had been settled elsewhere.Mr. Digby need not apologise for the details of his experiments, however. He would ask Mr. Digby how his hypochlorite had been prepared, and how transported, and how the metal couples were arranged. Could not the strong effect of the ebonite-metal couples be due to the action of the sulphur of the vulcanised rubber and of the alkali? Mr. L. A. Smart stated that he was not surprised that Mr. Digby had met with difficulties when endeavouring to impregnate wood with bitumen merely by boiling. He had recently been called upon to examine a new process for impregnating wood with creosote, fire-proofing solutions, &c., and was surprised to find, on investigation, that with the ordinary processes of creosoting, the liquid seldom penetrated the wood more than three-eighths of an inch except at the ends of the log, but by the new process which he had examined, they were able to put creosote or fire-proofing solutions through a log of wood twelve inches square and nine feet long-in fact, when the log was split open, there was not the slightest indication of the creosote havingfailed to reach any part of the timber.This process utilised super- heated steam by atmospheric pressure. Mr. W. Pollard Digby (communicated reply) : In reply to Dr. Rideal I am quite willing to concede that the temperature of the electrolyte is not the only factor governing hypochlorite stability. The quantity of alkali in excess is of considerable importance. But I have several records of very rapid depreciations occurring in solutions which had been treated with a definite excess but had been allowed to become heated, whereas other solutions with the same excess of alkali which had been kept cool were quite stable. In reply to Dr. Borns, the solutions used in my experiments were made by the electrozone process with a slightly modified form of the Crawford electrolyser. Transport was effected in glass bottles. The arrangement of the galvanic couples is described in the Paper, it being only necessary to add that they were suspended in open glazed earthenware jars. The suggestion as to the effect of the sulphur in the ebonite as the root cause of the exceptional depreciation seems a very helpful one. Mr. Smart’s proposal that bitu- menising should be effected by the new process he referred to was of great interest. But even given a perfect method of impregnating with bitumen, it seems that bitumenised wood should only be used for purely temporary work.

ISSN:0014-7672    

DOI:10.1039/TF9070200180

出版商:RSC    

年代:1907

数据来源: RSC

摘要:

THE HERMITE ELECTROLYTIC PROCESS AT POPLAR. By CHARLES V. BIGGS, M.S.E., A.I.E.E. ( A Paper rend before the Faraday Society on Tuesday, November 13, 1906, DR. F. MOLLWO PERKIN, TREASURER, in the Chair.) This Paper is a contribution to the data at present available on the subject of the electrolytic production of hypochlorites. It is unnecessary here to recapitulate the history of the various processes for effecting the electrolysis of chlorides so as to produce hypochlorites, or to allude to the purposes for which hypochlorite solutions are adapted ; for purposes of reference these subjects are briefly treated of in Appendices A and C. The utility of the substance being well proved by practical experiment and by scientific investigation, it only remains to show how it may best be produced on a commercial scale.A variety of processes are in existence, and of those which have been reduced to a practical form the best known are the “ Her- mite,” “ Electrozone,” and the “ Oxychloride.” Which of these processes is the most advantageous at present, i e . , which produces the largest quantity of stable fluid for the least expense in electricity, labour, and salt, is a question which only careful observation of the apparatus under working conditions can properly decide. Unfortunately, hitherto, the accessible examples of plants actually working on more than an experimental scale (involving the constant and costly alterations natural to experiments) have been extremely few ; the author only knows of one in this country, namely, the Hermite plant at Poplar.The following data have therefore been collected from runs under- taken at this installation in the ordinary course of working for supplying disinfectant to the borough. They go to show the eminently practical nature of this installation, as well as its efficiency, and the small amount of supervision and labour which is necessary. The system adopted at Poplar is to mix a certain quantity of fluid in an elevated tank, and then to allow this fluid to flow through four double troughs or cells, placed one above the other so that the liquid descends continuously by gravity. Each trough is divided laterally by a partition, and in each of the two divisions five distinct “ elements ” (consisting of one positive and two negative plates) are suspended (Fig.I). The positive plates are of thin platinum wire wound upon slate slabs and the negative plates are of zinc. There are thus four troughs each containing ten ‘‘ elements,” or forty cells in all. The liquid enters through the funnel visible towards the top left-hand side of the illustration, passes along the front division of the top trough, back through the division behind, over a weir and into a sub-division, from which it is drawn off by the bent glass tube discharging into the second funnel ; it passes along the front division, back through the division behind, over the weir into the pocket of the second trough, and so on to the final bent tube, which discharges it into a carboy. A bottle arranged at the right- hand side of the tier of cells supplies the sodium hydroxide used as a preservative, which flows drop by drop into the carboy as it is filling and 182FIG.I.-General View of the Poplar Plant.THE HERMITE ELECTROLYTIC PROCESS AT POPLAR 183 serves to neutralise free hypochlorous acid. As the liquid passes through the troughs it is subjected to the action of a current of 15 amp. at 230 volts, being 5-6 volts per cell. During the run the liquid in the carboy is thoroughly stirred by means of an ebonite rod provided with rubber flaps, and as each carboy fills it is subjected to a further stirring by means of the same appliance hung from a set of gear-wheels. This is an improvement introduced by Dr. Alexander, and obviates shaking the carboys. As each carboy contains 15 gallons, and will therefore weigh when full, with its case, something like 200 lbs., the impracticability of the latter process is obvious. The total space occupied by the electrolysing plant (including the tank) is 7 ft.by 7 ft. The capacity of the tank is some 215 gallons. The total head-room is 10 ft. During a run of eight hours 185 gallons of hypochlorite solution at a strength of over 4 grammes per litre are made. The procedure is as follows :- The tank is charged by placing in it IOO litresof a saturated solution of sodium chloride and 20 litres cf a saturated solution of magnesium chloride. To this is added as much water as is needed to bring the whole quantity up to 840 litres (185 gallons). The liquid flows from a pipe in the bottom184 T H E HERMITE ELECTROLYTIC PROCESS AT POPLAR Grammes per Litre.of the tank, at the end of which is a ball-valve, into a small flushing cistern at the side, in order to obtain an even flow, otherwise as the tank emptied the flow would be slower; thence through another pipe into the funnel leading to the first row of cells. The second pipe mentioned has a cock for regulating the flow. The rate of flow adopted is 33 pints (1.9 litres) per minute. This works out at 2 5 gallons (113.5 litres) per hour, or about 185 gallons (840 litres) in the eight hours. The chemical action taking place in the cells is described by Dr. Hodgkinson as quoted in Appendix C. It appears that the NaCl acts as a vehicle for the current ; the Mg and C1 ions being given up at the - and + poles, and combining with H,O to form Mg (OH), and 2HC1, with 2HC10, H, being given off.A final re-combination takes place, leaving MgCl, and Mg(OCI), with a little Mg(OH), as waste. The results of four runs with different currents are shown below :- Temperature. Gramrnes per H . T . ~ . 'OitS. I Tank. I IstRow. - 4.818 4'968 4.818 - 10.0 I 0.40 11.5 I 1.30 11.20 - 17 232 60.5 - - 138 17 232 - 72'5 95'5 142 17 232 - - 18 234 - 139 17 230 - 94 - - - - - I2 I2 I2 12 - 2 j o 3.0 3.10 3.30 3.45 214 - 212 212 212 - - 16 224 61 - - - - 16 224 - - 93 4'818 149 16 228 60 7 0 94 4'676 17 16 230 - 71 03 16 230 -- 70 93 - - Final. Remarks. Room Temp. 62O Flow 1.9 litres per min. 113.5 litres per hour. (3Q pints) I 1 j o 12.15 12.30 12.45 12.0 12.20 - 5'3 5'3 5'48 I 9 20 20 20 20 20 80 91'5 95 98 98 98 Room Temp. 64" 12.55 1.45 2.0 2.15 2.30 Temp.falling owing to reduced current. The currents employed were those which the rheostat admitted. The plant is designed to work at 15 amp. and a flow of 1-9 litres per minute. The curves which have been plotted from readings taken on these runs are appended (Figs. 2 and 3). The abscissae on Fig. 2 are merely arbitraryT H E HERMITE ELECTROLYTIC PROCESS A T POPLAR 185 h3 3 c186 THE HERMITE ELECTROLYTIC PROCESS AT POPLAR divisions indicating that the liquid has passed through one set (of ten electro- lysers), two sets, three sets, or four sets (final liquid). The ordinates show the strength obtained in grammes per litre. It will be noticed that the increase of I gramme per litre in each ten cells is fairly maintained, but has a tendency to fall off after thirty cells.Fig. 4 gives the rise in temperature for each amperage from the tank toTHE HERMITE ELECTROLYTIC PROCESS AT POPLAR 187 Temperature difference between Tank and Final Liquid. the final liquid. The high amperage naturally gives the greatest difference 21" C. (38" F.), the low amperage the least, 11" C. (zoo F.). Figs. 5 and 6 show rise in temperature of the liquid during I&-hour runs. It appears that, after attaining a certain temperature (270 C. (80" F.) and 37" C. (98" F.) respectively) the tendency is to increase slowly. Temperature of Final Liquid when made. f t s 6. (I) 15 O C. 27" F. ( 2 ) 14.5" C. 260 F. (3) 15 O C. 27" F. (4) 14.5" C. 26" F. Fig. 3 shows the efficiency curves, i.e., the grammes of chlorine per B.T.U.It will be noticed that the highest efficiency is obtained at 16 amp,; also that the last row of cells does not show so good a result as the others, or rather that the efficiency becomes less as the strength is higher-a point generally observed on these plants. The fact that a run at 17 amp, gives worse results than at 16 is not easily accounted for, unless it was due to stable conditions not having been reached on the 17-amp. run. Another run at 17 amp., not plotted, practically coincided with the run at 16 in grammes per litre, but must obviously be worse as regards efficiency. The tempera- ture differences were 17" C. (30" F.) for the 17, and 19" C. (34" F.) for the 16-amp. run. The high temperatures at which some of the samples have been made are interesting, in view of the widzspread belief that the hypochlorite solution deteriorates rapidly if made under such conditions.Samples were taken from solutions made and bottled during the warm weather of last summer with the following results :- 40" C. 104" F. 0.5 6 weeks. 40°C. 104" F. 0.2 4 9 , 40" C. 104" F. 0'1 6 ,, 34°C. 93" F. 0'1 6 ,, STABILITY TABLE. I.* * The liquid tested had been kept in ordinary dark glass bottles, corked.188 THE HERMITE ELECTROLYTIC PROCESS AT POPLAR While on the question of stability the following tables will be of interest ; the liquids in question were kept in carboys, not in small bottles :- I. Made 13/3/06. C.C. NaOH 300, tem. 76. 1 3 13 106 4'184 3/5/06 4.184 19/9/06 3'975 2. Made 13/3/06. C.C. NaOH 300, tem. 76. 13/3/06 4297 3/5/06 4'297 19/9/06 4784 3.Made 23/3/06. Temp. 72. 27/3/06 4'297 3/5/06 4'297 19/9/06 3'975 49 Made 26/2/06. Temp. 74. 5/3/06 4.416 3/5/06 4'416 19/9/06 3'975 5. Made 29/3/06. C.C. NaOH 300, tem. 76. 30/3/06 4'968 26/5/06 4'968 19/9/06 4'4'6 6. Made 23/2/06. C.C. NaOH 200, tem. 74. 23/2/06 5-30 28/2/06 5-30 2/3/06 5'129 3/5/06 5.129 19/9/06 4.8 I 8 7. Made 23/3/06. Temp. 72. 27/3/06 4'297 3/5/06 4'297 19/9/06 3'975 8. Made 29/3/06. C.C. NaOH 300, tem. 78 30/3/06 4.818 10/4/06 4'676 3/5/06 4'676 19/9/06 4'297 9. Made 12/2/06. C.C. NaOH 225. 12/2/06 3'785 3/5/06 3'785 19/9/06 3.613 The specimen made on October 2nd at a temperature of 104" F. = 40" C. and a strength of 5'4 grammes per litre, was tested three hours later to see if immediate depreciation took place in the hot liquids, but it was found to be unaltered, practically.The test gave 5.3 for the whole carboy, which con- tained more 5'3 than 5-4 liquid. The principal conclusions to be drawn from the working of this plant appear to be the following :- (a) The manufacture of hypochlorite solutions can be carried on by a process which is practically automatic. For an output of zoo gals. per eight hours at 4 grammes per litre the capital cost, including buildings and fittings, should not exceed Nhere continuous current is available the series system of electro- lysing is the most suitable. Where alternating current only is to be had, and a motor-generator must be installed, fewer cells may be employed. In the Poplar plant about I gramme per litre is added for every ten cells.I'hat a warm climate would not affect the manufacture at any rate of the magnesium hypochlorite. Esw.T H E HERMITE ELECTROLYTIC PROCESS AT POPLAR 189 In conclusion, the author wishes to acknowledge his indebtedness to Dr. Alexander, the Medical Officer of Heath for Poplar, for giving him every facility for inspecting and testing the plant, and for the use of blocks, for illustrations appearing in the Paper. The improvements suggested by Dr. Alexander which have been introduced in the plant in question are numerous, and it is largely due to them that the running has become the simple process described. APPENDIX A. NOTES ON THE HISTORY OF THE HYPOCHLORITE PROCESSES. The basis of the electrolytic hypochlorite processes has been well defined as producing chlorine at the anode, and the hydrate of the base (sodium or magnesium) at the cathode. In 1851 Charles Watt patented a simple electrolysing cell, in which hypo- chlorite could be produced.In the description the use of this substance for bleaching is suggested. About 1884 the Hermite electrolysing cell was introduced. The early forins used a revolving kathode. The plant at Poplar is an improved form by the same inventor. The objection formerly urged against this process, viz., that the product was unstable, does not now hold. Woolf’s electrolyser appeared about the same time as the Hermite. It consisted of zinc and platinum electrodes suspended in a tank ; originally sea-water was used as the electrolyte, but found to give unstable liquid. The reasons for the slowness of the solution to come into commercial use appear to be : Heavy initial outlay caused by the necessity for using platinum for the anode ; instability in the early liquids ; and general lack of confidence in the working plants due to insufficient trials and constant improvements and alterations.APPENDIX B. CHEMICAL ACTION. oc1 Dr. W. R. Hodgkinson says : (‘ MgoCl MgCI, is a somewhat unstable substance even at low temperatures in the presence of water. Although produced in the presence of sodium chloride during electrolysis, the ten- dency to combine with it is not so great as when the sodium chloride is formed in contact with it, or in a so-called nascent state. (‘Thus, when sodium hydrate is added to the MgO,CI,MgCl, solution, the following change takes place- The magnesium-sodium double salt being considerably more stable than the corresponding magnesium one.”190 T H E HERMITE ELECTROLYTIC PROCESS AT POPLAR APPENDIX C. VALUE OF THE FLUID.The practical value of hypochlorite solutions of a certain strength (2 grammes per litre and over) as deodorants and disinfectors has been frequently proved. The Riker’s Island example, in which the fluid was used to deodorise an enormous garbage heap near New York (1895), is well known. Sir H. E. Roscoe investigated the Hermite process (as it then was) in the same year, and came to the conclusion that a solution of as low a strength as 0.25 grammes per litre would destroy non-sporing organisms, but would not affect bacillus subtilis. Also that the 0.25 g.p.1.solution was an excellent deodoriser. Prof. Kanthack, in 1898, in inspecting the plant at Maidenhead for sterilising sewage effluent by means of this fluid, found that satisfactory sterilisation was effected by a 2-gramme solution used in the proportion of 2 gallons of solution to 1,000 gallons of sewage. In 1904 similar experi- ments were made at Guildford under Dr. Rideal, and the sterilisation effected was found to be satisfactory. A P P E N D I X D . RUNNING COSTS. From the figures given it will be seen that in an ordinary run of eight hours the electricity consumed will be- - 3-6 units per hour 240 x 15 At Id. per unit this will cost 2s. Sd.-say 2s. 6d.-per 200 gallons of the fluid. With sodium chloride at 40s. per ton, and magnesium chloride at -& per ton (high prices), 185 gallons (omitting the first carboy drawn off, 15 gallons, the bulk of which has only been through one row of cells) can be produced for- s. d. (NaCl) salt . . . . . . . . . . . . . . . . . . . . . I 6 Magnesiutn chloride . . . . . . . . . . . . . . . I o Electricity . . . . . . . . . . . . . . . . . . . . . 2 6 Attendance and labour, say . . . . . . . . . . . . 4 o 9 0 Interest on Esoo at 44 per cent., say 2s. per run ... 2 o - Total . . . . . . . . . . . . . . . 11 o Reductions in the price of salt could be obtained by buying in bulk. If the disinfectant plant were made an adjunct to the borough electrical generating station the cost of attendance could be reduced. Probably, including bottling and depreciation of plant, gd. per gallon is a fair estimate for the smaller sizes of plant.T H E HERMITE ELECTROLYTIC PROCESS AT POPLAR 191 APPENDIX E. TITRATION TEST EMPLOYED FOR TESTS AT POPLAR REFERRED TO. Five cubic centimetres of arsenious acid are run into a dish, and a drop of indigo added. The liquid to be tested is then allowed to flow into the coloured arsenious acid until the colour disappears. The amount of liquid required to bleach out the indigo being known, the chlorine intensity can be read from a table.

ISSN:0014-7672    

DOI:10.1039/TF9070200182

出版商:RSC    

年代:1907

数据来源: RSC

摘要:

T H E HERMITE ELECTROLYTIC PROCESS AT POPLAR 191 DISCUSSION. Mr. J. B. C. Kershaw (communicated): Mr. Biggs has made strange mistakes in his quotations from my article in Electrochemical and Metal- lurgical Industry (April, 1906), and I must therefore ask to be allowed to give the correct version of the introductory passage from which he has gathered his extracts :- “The electrolysis of solutions of the alkali metal chlorides always produces chlorine at the anode, and the hydrate of the base (sodium, potassium, or magnesium) at the cathode. In the electrolytic alkali processes the aim of the inventor has been to effect removal of these products beforc they can react one with the other. In the electrolytic bleaching and disinfecting processes the chlorine and the caustic hydrate are allowed to react, in order that the chemical changes represented by the following equations may occur :- “ (I).3NaOH + 6C1= 3NaOC1 + 3HCl (sodium hypochlorite and hydro- chloric acid). “ ( 2 ) . 3NaOH + 3HCl = 3NaCl + 3H,O (sodium chloride and water). “If the temperature be allowed to rise above a certain point, 120~ F., a further chemical action will occur, and chlorate will be produced. I t is, therefore, necessary in all electrolytic bleaching and disinfecting processes to pay great attention to the temperature, as chlorates are useless for bleaching purposes. (‘ The production of hypochlorite solutions for bleaching and disinfecting purposes by means of electrolysis has undergone little development in the United Kingdom, and only two types of cell are known to the writer to be at present in operation, namely, the Vogelsang and the Atkins cells.‘( Early in the nineties a considerable amount of money was expended, however, upon experimental trials with the Hermite cell for sewage purification and sterilisation, and much attention was given to the results of these trials. The failure to establish this method of sewage treatment upon a commercially sound basis led to the bankruptcy of the firm financing these trials, and to a collapse of interest in all processes and cells for producing by aid of electrolysis a solution containing free chlorine for bleaching or disinfecting purposes. It is only lately that attention has again been given to this subject of sewage disinfecting and sterilisation in the United Kingdom, the proposal of the Medical Officer of Health for Poplar to use electrolytic hypochlorite for disinfecting purposes within the borough having aroused considerable interest.‘( The low price at which hypochlorite of lime, or ‘ bleach,’ is now selling in the United Kingdom (A4 10s. per ton), is likely, however, to hamper the extension of these processes, for it is more than doubtful whether any of them can compete in price with the older bleaching agent. For certain192 THE HERMITE ELECTROLYTIC PROCESS AT POPLAR purposes, hypochlorite of soda is much to be preferred to hypochlorite of lime, the active agent in bleaching powder ; and in these cases the higher cost of the former, even when produced by the electrolysis of brine, is unlikely to retard its utilisation as soon as a cheap, reliable, and durable electrolytic cell ior producing it is placed upon the market.The Hermite cell and process in its original form did not fulfil these conditions, and the same judgment must be passed upon many of the patented forms and processes which have succeeded it. Even with cheap power and a durable and reliable cell, electrolytic hypochlorite is unlikely to take the place of bleaching powder for ordinary bleaching purposes, until the price of the latter has advanced to over A6 per ton, and therefore the development of this industry is somewhat doubtful in countries where bleach is manu- factured in large quantities, by either the old Le Blanc or newer electrolytic processes.” The figures given in Mr. Biggs’s Paper support the opinion expressed in the final sentences of the above paragraph.With electricity at id. per unit (which by the way is less than it costs to produce in Poplar) 3-36 kgs. of active chlorine are obtained with an expenditure of eleven shillings. Taking bleaching powder at its present price, and allowing ;GI per ton for freight and labour charges, eleven shillings would purchase ten times this amount (or 35 kgs.) of active chlorine, in the form of calcium hypochlorite. Even allowing for the superior efficiency of the sodium magnesium salt as a sterilising agent, it is impossible to believe that there can be any economy in paying eleven shillings for what could be purchased for less than two. The Hermite sterilising installation at Poplar is simply therefore yet another instance of the foolish waste of money by municipal bodies in general, and by Poplar in particular.Mr. Biggs, in p. I of his Paper, states that the Poplar installation is efficient. A comparison of the yield with that obtained in other forms of hypochlorite cell shows, however, that 11.0 E.H.P. hrs. are required to produce I kg. of active chlorine, and that the efficiency is only 21’5 %, as compared with a power consumption of 6.57 E.H.P. hrs. and efficiency of 35.9 % for the latest and best form of hypochlorite cell. In closing this contribution to the discussion upon Mr. Biggs’s Paper, I may perhaps state that I am as keenly interested as the author in all electrochemical developments of a sound character, but that I am not anxious to see extensions of the industry similar to that initiated by Dr.Alexander at Poplar, since these in the long run only end in failure, and place hindrances and difficulties in the path of progress in other directions. Dr. R. S. Hutton : The general description of the Poplar hypochlorite plant is certainly of much interest, but it is to be regretted that the author has only given the most vague description of the data likely to be of the chief interest to the members of this Society. In the hope that he will see his way to supplement his Paper in this direction and thus considerably enhance its value, I venture to ask for information on the following points :-(I) Size and shape of electrodes and troughs. (2) Diameter and length of platinum wire on each anode. (3) System adopted for making the terminal connections to the electrodes. (4) Durability of the zinc cathodes.(5) Method employed to prevent the formation of an iiicrustation of magnesium hydrate or hydrated salts on the cathodes. In trying to collate the results of this process according to the system which is almost universally adopted in connection with hypochlorite plants, I have been pleasantly surprised to note the great improvement which has beenT H E HERMITE ELECTROLYTIC PROCESS AT POPLAR 193 effected since the Hermite process was first exploited in this country. From the data which are given it is, however, almost impossible to tabulate a com- plete record, and I feel sure many members would be grateful if the author would fill in the numerical values in the following lines, taking into con- sideration as far as possible the average results obtained at Poplar.- grams active chlorine per litre. - K.W.H. (B.T.U.) per I kilo active chlorine. - kilos salt (MgCl, + NaC1) per I kilo active chlorine. Concentration of electrolyte - kilos salt per IOO litres. Current efficiency - per cent. In Appendix A the author does not mention that Mr. Kershaw’s article pro- fesses to deal solely with the use of hypochlorite as a sewage sterilising agent. No account has been taken of the vast amount of work done on the Continent, and so ably summarised in Engelhardt’s monograph, “ Hypochlorite und elektrische Bleiche ” (Halle : W. Knapp, 1903), a book of 273 pages, con- taining invaluable data from the technical investigations of Kellner, Oettel, and numerous other active workers in this field.In considering Appendix B, I cannot resist the temptation of again referring to Continental work. Professors F. Foerster and E. Muller, of Dresden, devoted a number of years to a detailed study of the chemical and electro- chemical actions occurring in the electrolytic production of hypochlorites and have given an excellent risume‘ of their work (2. fiir Elektrochemie, Finally, in Appendix D no account is taken of the cost of the caustic soda additions mentioned in an earlier section of the Paper, and the question of depreciation is surely not covered by the low rate of interest allowed in the capital expenditure. In view of the increasing interest which is being taken in this country in the electrolytic production of hypochlorites, and the evident importance of the new Hermite plant at Poplar, I trust the author will excuse my request for so many further details.In reply to Mr. Kershaw’s criticisms on the efficiency of the Poplar cell, Dr. Hutton pointed out that efficiency depended largely on the concentration of the solution ; it was not possible to maintain a high efficiency with solutions of such a low concentration. Dr. F. W. Alexander, the Medical Officer of Health for Poplar, stated he was not a chemist nor an electrician, nor had he any financial interest in the Hermite process; he had simply taken up the subject from a scientific point of view. He had not benefited in any way by it and did not expect to do so ; he had worked for the love of the matter and he had no axe to grind.Were we living in the days of Galileo? He was astonished to think that in the nineteenth century every possible obstacle had been placed in his way through certain articles in the press advising his Council not to listen to him as the process had been a failure in the past and could not possibly be of any use, it would be waste of public money, and was simply a fad of the Medical Officer. If the process had been of any use it would have come into operation before. However, he had had the matter in his mind for many years since the publication of the report of the Lancet Commission, and had worked at the subject for nearly two years ; the working of the apparatus in Poplar was a complete success-it had come to stay-and it had gone quite beyond his expectations.No doubt the failure of the past had been due to the want of stability of the fluid, but this had now been got over, as is seen by Stability Tables I and 2 of the Paper, and the samples referred to in Table 2, be it remembered, were some of the first made before the use of the stirrers. It 1903,9* 171 and 195).194 T H E HERMITE ELECTROLYTIC PROCESS AT POPLAR was prophesied in the press that the formation of the oxychloride would choke or block the zinc electrodes, and that scrapers had been used in the past, but he would speak on this matter later on as to how the osychlorides were dealt with. It was also stated that chloride of lime would be better to use. He wanted to know how this substance could be bottled and given out to the public; one would have to mix it with water to dissolve out the calcium hypochlorite, and as the commercial powder contains 30 to 38 per cent.of available chlorine, the waste lime would have to be disposed of, and all this meant labour, and, moreover, chlorinated lime solutions will destroy fabrics sooner than hypochlorites of soda or magnesia. As to the cost of making the fluid, in Poplar the apparatus had been running since the end of January, a period of ten months, during which time there had been required 2,288 units of electrical energy at I$d. per unit, amounting to E15, not quite four tons of salt had been used at 24s. a ton, amounting to A4 I ~ s . , not quite two tons of chloride of magnesium at 153 17s. 6d. per ton had been used, amounting to &7 I ~ s . , the cost of the caustic soda was about A2 IOS., and water L2, making a total of E32, and this sum included material in hand.This expenditure did not include the labour, which really was less than in the old days when carbolic acid was bottled and bags were filled with carbolic powder and distributed to the public. He would speak later on with respect of this labour question. Now for the sum of E32, including material in hand, the Public Health Department had been supplied with disinfectant fluid against an expenditure of A313 for the year 1905, and, moreover, in the Works Department the roads, with the market- places, in the parish of Bromley had been watered with the fluid, and now the Sick Asylums at Poplar and Bromley were being supplied, also the Work- house and all institutions inside and outside the borough belonging to the Guardians.Surely this was success whatever the detractors of the process might say, and all this for the sum of L32. With respect to the watering of the roads and market-places, the water- carts in Poplar had a capacity of 400 gallons, and on the top of each cart had been fixed a small tank to hold 15 gallons of the electrolysed fluid. Five gallons of this fluid were added to each 400 gallons of water, giving a strength of 0.05 grammes of chlorine per litre. He had based this strength on a state- ment of Dr. Rideal that in ‘‘ Experiments conducted by Professor Robinson, Dr. Kanthack, and myself a bad effluent was treated with one or two parts of chlorine per 100,ooo with very satisfactory results as regards bacteria.” Now as to the working of the apparatus one man only is required, and he not a skilled one, merely an ordinary intelligent individual, at 35s.per week. He attends to the charging and working of the apparatus and the testing of the fluid, and keeps a log of each day’s work and distribution. It is true there is another man at the dep6t with wages of 30s. per week. This man is engaged in bottling and delivering the fluid for distribution, and he is also quite capable of looking after the apparatus. Formerly in the fluid and carbolic acid powder days during the busy time six or seven men were at work. The object of the Medical Officer was to make the working of the apparatus of such a nature as to be simple and automatic and not to require the constant attention of a skilled person, who would receive a high salary, and men to do the labour work, which would increase the cost of the output.The objects aimed at were as follows :-- This is accomplished by a gauge glass in front of the large tank and another gauge I. To see at a glance whether the apparatus were working properly.THE HERMITE ELECTROLYTIC PROCESS AT POPLAR 195 glass on the little supply tank, the first to show the quantity of salt liquor capable of being acted upon, and the second to show if the liquor is running properly into and out of the small supply tank, as the chloride of magnesium contains impurities which are likely to block up the valve of the small cistern and the taps leading to and from the same. A thermometer is kept in the small supply tank to see the temperature of the salt liquor, and another thermometer is placed at the outgo of the last electrolyser ; the difference of the temperatures will give a measure of the electrical heat, which is found when the apparatus is working satisfactorily to be under 30” F.The small tank is necessary to keep an unvarying flow of the fluid into the electrolysers. When first the apparatus was erected the fluid used to become unduly hot on account of the flow slowing down through the diminution of the head of water in the large tank, This tank had ultimately to be raised on two girders and a small supply tank fixed at a lower level. 2. The liquor to be electrolysed in the large tank has to be stirred from time to time to keep the mixture of an equal gravity throughout, more especially as for obvious reasons a certain quantity of a solution of sodium hydroxide is added. To keep the liquor stirred a large broad drilled plate of galvanised iron is used, one end of which acts as the fulcrum when the other is lifted up by means of a chain leading over pulleys to the ground, so that the attendant has only now and again to pull the chain to lift the plate up and down instead of running up and down the ladder and stirring the liquid with a rod.3. It is necessary to govern the electric current, especially as the dep6t is so near the electricity works and the current is taken off direct from the mains, and also on account of the density of the salt mixture to be acted upon varying from time to time, no doubt due to the temperature changes of the air, for the more sodium and magnesium in the liquor the greater is its conductivity.This difficulty is got over by the current regulator. 4. To prevent shocks and waste of fluid whilst changing the carboys a special glass tap has been made. 5. To prevent loss of available chlorine the solution of sodium hydroxide drips into a specially blown carboy at the same time as the fluid is running into it, and the two fluids are mixed with a stirrer inserted through an aperture in the neck of the carboy, and when the carboy is full a final mixing for about two minutes is given by means of a stirrer fixed to gear wheels. Before the ebonite stirrers with rubber flaps were made, full carboys and half carboys had to be shaken rapidly for ten minutes, and this not always with the best results as to bringing about the desired stability, for when sodium hydroxide is added the precipitate falls to the bottom, and it is neces- sary to render the solution milky throughout.Dr. Alexander stated that no doubt the instability of the fluid was due to the salt in the fluid. M. Hermite made a fluid for medical purposes called “Hermitine,” which had the salt taken out of it by a secret process, and thereby the fluid was rendered practically absolutely stable, so much so that it was not kept in amber-coloured bottles, but for disinfecting purposes the fluid niade at Poplar was of course stable enough. The plant at Netley was still running satisfactorily, but in that case a stable form of hypochlorite was not required.6. So far as oxychlorides are concerned the apparatus in ten months had only been taken to pieces and cleaned twice. Every day after working the electrolysers are emptied by means of the mud-holes by removing the rubber plugs, and the fluid which is run out is kept to recharge the electrolysers. The electrolysers after being emptied are washed by means of a hose, and196 THE HERMITE ELECTROLYTIC PROCESS AT POPLAR then until the next working are kept filled with water, which softens any deposit which forms upon the electrodes, and before starting work the electrolysers are emptied and washed out again, a matter which takes up a few minutes every day before and after each working. Dr. Alexander mentioned he had seen an exceedingly simple apparatus in M.Hermite’s factory at Rolleville which makes a solution of hypochlorite of magnesia at 10 grammes of chlorine per litre, and it was a very easy matter on the same lines to make it at 50 grammes per litre, but he of course could not give details to the Society, as the apparatus was shown to him in confidence. He thanked Mr. Bowden, the chief electrical engineer to his borough, for the kindly words of cheer which he gave him during the exceedingly trying time when he was endeavouring to make the apparatus work simply and automatically, and to render the fluid stable by simple means, so that he could justify himself for having recommended his Council to expend public money for such a venture. In conclusion, whatever the detractors of the process might say, there was no doubt in his mind the process had now come to stay, as it was obvious in these days of cheap electricity nothing could be better for a sanitary authority than to possess a simple automatic apparatus which has a tap to be turned on at any moment to deliver a cheap and efficient disinfectant composed of oxygen and chlorine.The members were invited to inspect the apparatus. Dr. S. Rideal, both as a chemist and bacteriologist, said that he had had a good deal to do with the various electrolytic processes, and had an oppor- tunity many years ago of carefully studying the Herniite process when installed at Worthing, and since that date at Netley. Later, in conjunction with Professors Kanthack and Robinson, he carried out a series of experiments at Maidenhead with the electrozone process, and there established the con- ditions for successful steriIisation of sewage effluents.More recently still he had examined the Atkins plant, which had for some time been in operation in connection with the sewage works at Guildford, and he had there con- firmed the results earlier obtained at Maidenhead, and had satisfied himself that electrolytic chlorine was not only capable of sterilising sewage effluents after bacterial treatment, but could be advantageously employed for reducing the odours from septic tanks and from sludge when necessary. Quite apart from sewage sterilisation there was a wide field of applicatibii for hypochlorite, provided it could be made economically, and he quite supported the claims made by Dr. Alexander for electrolytic chlorine as against bleaching powder, even when the former was more expensive.The convenience of being able to make the fluid on the spot-to turn on the tap so to speak-as required, and the absence of transit difficulties weighed more strongly than cost for ordinary disinfecting requirements, and there was no doubt that it would be more largely used as its value became known. He had a high opinion of the value of watering streets with a sterilising fluid, as the germs in dry horse refuse and other dust were certainly sources of danger ; indeed the dust nuisance caused by motors now rendered the use of a sterilising fluid a necessity for street watering. Cost, therefore, was by no means an all-important consideration, and in any case the cost of electrolysis was quite small. The early processes were costly chiefly on account of the material ; for street watering some material had to be used, and this factor was therefore negligible. I n sterilising the cost was made great on account of the large amount of undecomposed salt present.The most successful cell gave a maximumTHE HERMITE ELECTROLYTIC PROCESS AT POPLAR 197 amount of free chlorine from a given quantity of salt, and it was in this that the early cells fell short. An incidental disadvantage of undecomposed salt in certain cases was that it must not be introduced into drinking water. Stability, as had been pointed out, was an important quality, but it was difficult to say exactly on what it depended ; the temperature of formation was not the only factor, he thought that it depended rather on the quantity of alkali present.Mr. Lewis A. Smart said that the process particularly appealed to him, as he looked at it from the point of view of a consulting engineer, who had to design and control central electric power stations. The great trouble with power stations, particularly if the load is largely a lighting one, is to get a high load factor. It appeared to him that processes such as this would have a beneficial effect on the load factor, and consequently on the cost of electricity to the consumer, especially if the enterprise belonged to the same people as the power station, and within certain limits, was under the control of the station engineer, as then, when the peak of the load was reached, the electrolytic process could be cut out for an hour or two, though in the case of the manufacture of hypochlorite, the load would presumably only be required between the hours of 6 a.m.and 6 p.m., so would not come on during the hours when the peak of the load curve was generally reached. Mr. Smart’s only regret was that the process did not consume more power, and he believed that the Society would be doing yeoman service to mankind in general, and to public supply engineers in particular, if it could draw attention to electrolytic pro- cesses which could be remuneratively adopted by power station owners, and utilise current during the hours when the lighting load was small. Mr. Wolf Defries said that in comparing the cost of hypochlorite with that of chloride of lime it must not be forgotten that although the two materials would be on a level as regards variations in prices of raw material, the former always contained an element of cost due to current, and this had a tendency to decrease as time went on.The future, therefore, would favour electrolytic hypochlorite rather than bleaching powder. But, as had rightly been pointed out, the ultimate cost-to the consumer-depended on how the product was to be utilised, and questions of convenience, ease of transport, and so forth, became in many cases determining factors. In his opinion Dr. Alexander had performed a public service in taking up and developing a process that seemed so unattractive, and was certainly so unpopular when he first adopted it to meet his own special requirements.Mr. C. V. Biggs (communicated reply) : I am obliged to Mr. Kershaw for calling my attention to an error in Appendix A. The repetition of the word ‘‘ hypochlorite ” in the original attributed to him sentiments chemically indefensible, and the paragraph has been altered accordingly. Mr. Kershaw’s contention that the use of hypochlorite solution as made by the Hermite process is inefficient has been dealt with by Dr. Hutton, Dr. Rideal, and Dr. Alexander. The generation of electricity from coal is also an inefficient process, but it is convenient and expedient. Mr. Kershaw remarks that Id. per unit is less than the cost of pro- duction at Poplar. The latest quotation for power in bulk there is o.85d. per unit. With regard to Dr. Hutton’s request for more precise information as to the cells, I did not consider it fair to the makers to take exact measurements, From memory I should say that the electrodes measured about 10 in. x 3 in, Each trough contained ten cells (one positive and two negative plates each) and an end compartment, being 4 feet long, over all. The platinum wire on the positive appeared to be of 20 S.W.G. This would suppose 30 wires198 T H E HERMITE ELECTROLYTIC PROCESS AT POPLAR in parallel to each positive plate with an average length of I foot. wires were connected to a terminal screwed into the plate. water after each run. the data taken is 4.5. active chlorine = 13-5. These To obviate incrustation on the cathode the cells are washed out with The average grammes per litre obtained with 16 amps. at Poplar from K.W.H. per I kilo of chlorine (at 16 amps.) = 7’2. Kilos salt per kilo The calculations for this are given below. 20 litres of saturated solution of MgCl contains 10 K. salt. 100 7, 9 , 9 , NaCl ,, 40 K. ,, 40 + 10 = 50. 840 litres at 4-5 per litre = 3,780 = 3.7 kilos. Concentration of electrolyte :- Kilos salt per IOO litres = 50- = 5’5. 9-07 I am obliged to Dr. Hutton for calling attention to that admirable work of reference, V. Engelhardt’s ‘ I Hypochlorite und elektrische Bleiche.’’ This work was quoted from in the Paper read before the Society on October 31, 1905, and is doubtless well known to the members.

ISSN:0014-7672    

DOI:10.1039/TF9070200191

出版商:RSC    

年代:1907

数据来源: RSC

摘要:

ON T H E ELECTROCHEMISTRY OF LEAD. By ALEXANDER CHARLES CUMMING, D.Sc. (1851 Exhibition Research Scholar). ( A Paper rend before the Faruday Society on Tuesday, November 13, 1906, DR. F. MOLLWO PERKIN, TREASURER, in the Chair.) In all the well-known salts lead is a diad metal, but it has been proved that other salts exist in which it is tetrad. For example, Kikoljukin (Berichie 1885, p. 370, Ref.) by suspending lead chloride in strong hydrochloric acid and passing chlorine through the solution, obtained PbCI,, which could be precipitated as the double salt PbC1,2KCl by addition of potassium choride. Elbs and Niibling (Zeit. fiir Electrocli. 1903, p. 777) have prepared plumbic sulphate, Pb(SO,),, and various double salts by electrolytic methods. Various other experimenters have prepared plumbic salts, usually as a double salt with an alkali salt. The simplest of these methods seems to be that of Seyewitz and Tawitz (Cornpies Rendus, 136, p.686), who, by the action of ammonium persulphate on lead chloride and hydrochloric acid at a low temperature, obtained plumbic ammonium chloride. Although the double salts have been obtained in an approximately pure state, it has not yet been found possible to prepare any pure, simple plumbic salt. Elbs and Fischer (Zeit. fiir Electrocli. 7, p, 343 (1901)) have shown that plumbic sulphate is formed when a current is passed between two lead plates in strong sulphuric acid, and the electromotive force of an accumulator may therefore be regarded as caused by the tendency of plumbic ions, formed from the lead peroxide and sulphuric acid, to transform into plumbous ions with liberation of the extra electric charges (Abel, Zeit.fiir Electroclt. 7, p. 731). The tendency of any ion (i) to be transformed into an ion (0) with a lower valence may be measured by means of an oxidation electrode. If the difference in valence between the i and o form be n, the electromotive force in volts- '0591 C = P + T - l o g , , C, (at 25,) where P is the tendency of the i form to change into the o form when t h e concentrations are equal, while Ci and C, are the actual concentrations of the i and o ions respectively, which are used in the experiment. The value P is always given in comparison with some standard such as the normal hydrogen electrode (Wilsmore, Zed. .fiir physik.Ch. 35, p. 291 (1900)) on account of the uncertainty of the absolute values, and is characteristic of the particular element under investigation. 199200 ON T H E ELECTROCHEMISTRY OF LEAD Further- Krr P = nt; log, k where k is that particular ratio (2). of the i and o ions with which the tendency becomes equal to that of the standard taken, so that we have RT n F Up to the present no estimate of the magnitude of R or P for Pb * * * * + Pb.. has been made, though for a knowledge of the chemistry of lead this deter- mination is as important as the value Pb.. * metallic Pb. I n order to obtain R or P, the values of Ci and C, must be known ; or for the special case of lead, the concentrations of plumbous and plumbic ions must be known. The easiest method would naturally be to obtain the two types of salt separately and mix them in known proportions.Attempts were made to prepare plumbic chloride and plumbic sulphate by the methods given above, but very poor yields were obtained, and these proved to be very crude. No method for the purification of a plumbic salt is at present known. This line of attack was soon given up, as it was found that plumbic chloride and sulphate were too unstable in aqueous solution to be of service, since the former evolved chlorine and the latter oxygen. Lead superoxide contains the lead in the tetrad condition, and if it could be brought into solution, should yield a plumbic salt. It dissolves readily in strong hydrochloric acid, but with evolution of chlorine, though doubtless some plumbic salt is also formed.The high solubility alone does not, however, prove that all the lead is not in the plumbous form, since much more plumbous chloride dissolves in strong hydrochloric acid than in water (von Ende, Z e d . anorg. Clz. 26, p. 129). It is generally stated that lead peroxide is insoluble in nitric acid, but as insolubility " is only a relative term, experiments were made to determine the extent of the solubility. It was found that at ordinary dilutions, the solubility was not analytically measurable, but that it became appreciable in strong solutions. It then became necessary to determine whether any estimate of the trans- formation tendency could be made in strong solutions, and what value could be placed on such an estimate ; and the following experiments were carried out with this aim.The temperature at which all experiments were performed was 25". I t was first found under what conditions the same potential could be obtained. The same nitric acid solution, approximately 5 N, was used in each experiment. Some of this acid was shaken for several days with lead superoxide, bought as pure from Kahlbaum, and to 20 c.cs. of this solution, 5 c.cs. of a plumbous nitrate solution were added. Two platinised platinum points, which had been polarised in dilute sulphuric acid against one another, served as electrodes. The potential varied irregularly at first, but after some hours both points were at the same potential. This came about much quicker if the points were placed in the lead superoxide at the bottom of the vessel.This potential was obtained still more quickly, if a platinum point which had been electrolytically coated with lead superoxide was used. Further, if a platinum point, coated with lead peroxide, were placed in a solution of the same strength for nitric acid and plumbous nitrate, but whichON THE ELECTROCHEMISTRY OF LEAD 201 had not previously been shaken with lead superoxide, an electromotive force was obtained which rose to the same value as had been obtained in the former experiments, and remained constant at that value. Evidently, then, this was a definite oxidation potential. The best form of electrode was found to be a small platinum plate, which was first platinised and then coated with lead peroxide, usually from a solution containing N nitric acid and some lead nitrate, as this was found to give a durable coat.Some incidental observations on lead superoxide may be mentioned here. The ordinary commercial lead superoxide is dark purple, and remains of this colour on long shaking with water. If shaken with nitric acid of any strength it becomes quite black, while with sodium hydroxide it becomes a bright red. When electrolytically deposited it is usually quite black, but on two occasions it was obtained with a reddish colour. On both occasions, a high voltage was used (10 volts), and there was nitric acid, about N, in the solution. The ordinary superoxide, which had been turned black by nitric acid, became purple and then red in caustic soda, but a sample of electrolytically prepared lead superoxide showed no trace of red after a week in 5 N soda.::: The figures for one typical potential measurement may be given in some detail as an example of the results obtained.Throughout the research, two electrodes, freshly coated with PbOs, were used, and if these did not agree the experiment was repeated. This, however, rarely happened. Unless specially mentioned, the measurement was made against a N calomel electrode with saturated ammonium nitrate as the connecting solution. I. The solution was 4-64 N for nitric acid, and contained 0-0100 grm.-mols. 11. The solution was 4-64 N for nitric acid, and contained O*OIOO grm.-mols. Before the measurement it had been of plumbous nitrate per litre. of plumbous nitrate per litre. shaken for two hours at 25' with lead superoxide.Time in Hours. 0 2 I7 I 8 23 24 25 20 I. Potentials in Volts. Electrode. I 2 ... 1.391 ... 1'394 ... 1.401 ... 1.398 ... 1.406 ... 1 '407 ... 1'407 ... 1.408 ... 1.408 ... 1.409 ... 1.406 ... 1.408 ... 1.408 ... 1.406 ... 1.408 ... 1'395 I 1 Timein Hours. 0'5 1 16 18 20 1 23 11. Potentials in Volts. Electrode. I 2 ... 1.420 ... 1.445 ... "417 1.409 1.409 1.406 ... 1'409 ... 1.408 ... 1.408 ... 1.408 ... 1.408 ... 1'408 ... 1.407 ... 1'408 ... 1.409 1.407 ... ... ... ... In both cases the potential became steady about 1,408 volt. It will be noticed that in the last reading with electrode 2 in Experiment I. there is a sudden drop of 0.011 volt. This was due to some lead superoxide dropping off, and the potential would later rise to the same value as before It was found that such variations occurred too often when the nitric acid had to saturate itself with plumbic salt at the expense of the electrode, since that * The following explanation of these phenomena has occurred to me since writing the above.The purple and black varieties of PbO, are allotropic modifica- tions. I t is a well-known fact that substances of high oxidation potential, such as PbO,, are much more stable in acid than in alkaline solution, and in the latter more readily evolve oxygen. There- fore PbO, in alkaline solution becomes red since it is transformed into PbO with evolution of oxygen. It may be that the change is very slow, in which case the PbO would be dissolved by the alkali as quickly as it was formed. The bright red substance is almost certainly PbO.This was not observed with the black variety.202 ON THE ELECTROCHEMISTRY OF LEAD is what must occur here. Consequently the nitric acid was always shaken with lead peroxide for several hours before use, and the lead peroxide was then found to stick to the electrode. It was found to be immaterial how long this preliminary shaking lasted, as the same results were obtained with acid shaken for 30 minutes and for 14 days. If, however, the plumbous concentration was to be very small, it was thought advisable not to prolong the time lest some decomposition of the plumbic nitrate should occur, with consequent formation of plumbous nitrate. Once the potential had become steady it remained so for many hours, and then started to fall slowly. Usually this fall in potential first became appreciable after about 24 hours, and appeared to proceed indefinitely.This may be due to the presence of a trace of chloride, or to a minute trace of platinum dissolved from the electrode. Solubility of Lead Superoxide i'n Nitric Acid at 2.5'. The nitric acid used contained no weighable amount of solid impurity in zoo c.cs. of concentrated acid. No chloride could be detected. The lead superoxide was washed several times with nitric acid before use. The solution was first evaporated to dryness, then some sulphuric acid added, dried, and weighed as sulphate. Milligrm. HN03 Time in '*". Of normality. thermostat. [:L::::r %$g:f nlols' Of Lead _h tl. 1 days. 1 estimation. 1 grms. 1 per:tre. 1 n4 5 30 7'50 7-50 9-20 9.20 11.5 I 1.5 7 5 6 7 6 8 20 0.0157 0.0254 0.0250 0.038 I 0.0350 0.0458 0.0723 0~00013 I o*o00132 0-ooo 130 o-ooot 17 0-000107 0*000086 0~00009 I b nJ(H,O)z 0'00020 0*00024 0*00024 0*00024 0~00023 0'0002 5 0.00026 Mean = 0*00024 If the lead in PbO, be tetrad, then by the law of mass action- PbO, + 2H,O Pb(OH), .g=2 Pb * * * * + 4(OH)'. (Pb * * * * )(OH')J = K - (PbO,)( H,O)', and since- In the above table (concentration Pb) - _ has been taken as an (concentration HNO,)4 - a4 (Pb * * * ) approximation for ~ (H ,>' .The active mass of pure water has been taken as I , and the calculation made on the assumption that the active mass of water decreases 3-6 per cent for each grm.-molecule of acid in the solution. A more exact estimate would have been obtained from the vapour pressures, but with the inexact values for Pb...* and H *, this is quite close enough. Since a and b are only approximations for H and Pb...., theON T H E ELECTROCHEMISTRY OF LEAD 203 constant is as close as could be expected, considering the very small value of b, the results agree with the hypothesis that PbO,, when dissolved in HNO,, yields tetrad lead ions. With this knowledge of the solubility, an approximate value for P may be obtained. To obtain the true value of P, the concentrations of plumbous (C,) and plumbic (Ci) ions in a solution, together with its oxidation potential, must be known. The electromotive force e was always measured at 25' against a N calomel electrode, and as it is usual to take the N hydrogen electrode as standard, we have- P = e + 0.283 + 0.0295 log '.volt. Ci It was not possible to measure Ci and C,, but as an approximation the values of Si and S,, the total concentrations of the plumbic and plumbous salts, were taken. According to the Abegg-Bodlander theory (Zeit. anorg. Ch. 20, p. 453, 1899), the tendency to form complex ions is in inverse order to the strength of the ions. Of the common ions NO: is one of the strongest, and in accord with this theory, Labendzinski (Znaug. Dissert., Breslau, 1904) found from E.M.F. measurements that there was far less formation of complex ions with metallic nitrates than with chlorides or sulphates. Spencer (Zeit anorg. Ch. 44, p. 379: 1905) in a more exhaustive investiga- tion of the particular case of thallium, found the same thing. Nominally any salt might be used for the determination of P, but the ionic equilibrium with a salt that forms both simple and complex ions is too iiivolved to allow of calculation.Accordingly, P for lead was deter- mined with the nitrate, on the assumption that it yields almost entirely simple ions. Elimination of Dzfusioia Potential. If nitric acid solutions of the same concentrations as were used in the solubility experiments were to be employed, only a very rough approximation could be obtained, unless some method of removing the diffusion potential was found. The application of Plancks formula (Pogg, Ann. 40, p. 561, 1890) to calculate this potential was obviously out of the question, so other methods were tried. The use of potassium chloride (0. F. Tower, 2. physik. Ch. 20, p.198, Bjerrum, 2. fhysik. Ch. 53, p. 428) and of saturated potassium and ammonium nitrates (Cumming, see further, pp. 213-220) as connecting solution between the cells was first tried at a comparatively low dilution so that the results might be checked by calculation. The electromotive force of a cell containing 0.897 N nitric acid and 0.100 mol. lead nitrate with lead superoxide as electrode, against a N calomel electrode, was as follows :- DIFFERENCE FROM CONNECTING SOLUTION. E.FgybELqr. E.M.F. WITH DIRECT CONNECTION. - Direct connection . . . . . . . . . . . . 1'221 ... Saturated potassium chloride ... F . 1-242 ... 0'021 Saturated potassium nitrate . . . . . . 1'233 ... 0'012 3 saturated ammonium nitrate . . . . . . 1242 ... 0-021 3 9 , 2 1 ,, 1-255 0.034 1 ,, ,, ,, .. . . . . 1'256 ... 0'035 . . . . . . ... The diffusion potential between two binary electrolytes of the same ionic concentration (Planck, loc. cit.)- VOL. 11-T8204 ON T H E ELECTROCHEMISTRY OF LEAD where u, and u, are the velocities of the cations and 7~~ and v2 the velocities of the anions. If we neglect the lead nitrate, and take the nitric acid and potassium chloride as of approximately equal concentration, we obtain- e = 0-059 x log 350 + 75 74 + 71 = 0.029 volt. The saturated potassium chloride removed 0.021 volt, and the saturated ammonium nitrate 0.035 volt. The latter value is probably nearer correct.'g Nitric acid =7*97 N, and 0.01 grm. mols. of lead nitrate with lead superoxide electrode, against a N calomel cell. DIFFERENCE FROM a.CONNECTING SOLUTION. E.M.F. Direct connection (a) . . . . . . . . . 1-440 ... - ,, ,, nitrate 1.457 ... 0.017 6 ,, ammonium ,, . . . . . . 1.451 ... 0.011 3 7) ,) ?, 1.483 0.043 1 ?, . . . . . . 1'515 ... 0.065 Saturated potassium chloride . . . . . . 1.490 ... 0.050 . . . . . . . . . . . . ... ,) 9 , As the observed E.M.F., with saturated ammonium nitrate as the connecting solution, is probably nearest to the true value, it was used in the following experiments :- Determination of P. In the next table will be found the results of a series of experiments to determine P within the same limits of nitric acid concentration as in the solu- bility experiments. The nitric acid was determined by titration ; the plumbic Strength of H NO3 8-8 8.8 8.8 8.8 8.8 7'97 7'97 7-15 7-15 7-15 7-15 7-15 6-88 6.88 Concentration of Pb IV Si 0*00060 0.00050 0~00026 0'00022 Concentration of Pb 11.so. 0000238 0.0-455 0.00238 0.00238 0'0 I00 0'00 I 0'0 I0 0'025 0.025 0.025 0.025 0.050 0'02 j 0' I00 E.M.F. against N calomel. 1'549 1'533 1'534 1'539 1.530 1-529 1.515 1.477 1'476 1 '479 1.476 1.476 1.465 1.459 E.M.F. against hydrogen standard. 1.832 1.816 1.817 1.822 1.813 1.812 1.760 1.759 1-762 1'759 1'7.59 1.748 1.742 1.798 P 1.825 1.815 1-829 1.850 1.821 1.826 1.827 1.826 1.829 1'826 1.826 1.817 1.820 1.834 Mean = 1.83 * In a paper to be read before the Faraday Society in December, 1906, an account of a systematic investigation into the use of strong ammonium nitrate to remove the diffusion potential will be found. It was shown that a saturated ammonium nitrate solution was the best method at present available for the elimination of diffusion potential in strong solutions.ON THE ELECTROCHEMISTRY OF LEAD concentration was taken from the table of solubility of lead superoxide in nitric acid; and the total plumbous concentration was known, since a definite amount of a standard plumbous nitrate solution had been added.C si has been used in the calculation of P, instead of -' S, C O ' The constancy of C S - the results makes it certain that 2 must be proportional to 2, and the co S O simplest assumption would be to take them as equal. There is a possible error in that all the lead dissolved by nitric acid has been taken as lead superoxide dissolving to form plumbic lead. If for any reason some really formed plumbous lead, the true value of So would be higher, and that of Si lower, so that 1-82 volt against the hydrogen standard is probably a minimum value.Experiments in more Dilute Solutions. It has been shown that the equilibrium constant for PbO, dissolving in HNO, to form tetrad lead ions is of the form- (Pb....) cHTHTG-u = constant. If it were possible to determine (H *) and (H,O), it would then be possible to calculate the value of P b . * * . in any strength of nitric acid solution. Our knowledge of strong solutions is at present too imperfect to enable this to be done, but as a first approximation we may, as before, take the total nitric acid concentration as a measure of H *, and calculate (H,O) as before. In this way values for P b * * . . in dilute solutions may be obtained, from which P can be calculated, and some such results are included in the following table.The formula used for the calculation of the amount of tetrad lead was :- PbTV = ( HN0,)?(H20)?:(ooooz4) grm.-equivalents per litre. H NO3 normality. 4.82 4-82 4-82 4-82 4-40 4 2 2 4-22 4-2 2 3'44 3'44 3'44 3'44 3'44 3'44 3'44 0.897 0.897 0.897 Active Mass of (H,O). 0.827 0.827 0.827 0.827 0.842 0.848 0.848 0.848 0.876 0.976 0'976 0'976 >oncentration of Pbrv. Sf. 0~000098 0*000064 0 ~ 0 0 0 0 ~ ~ 0.000026 0'0000002 Concentration of PbII. S O . 0'1 0'1 0'0 I 0'0 I 0'1 0'0 I 0'0 I 0'000 I 0'1 0'1 0'0 I 0'0 I 0'00 I 0'000 I 0'000 I 0'1 0'0 I 0'00 I so Si - E.M.F. against N calomel. 1-42 j 1 '424 I '443 1'439 1.417 1.407 1.409 1.444 1'379 1.380 1'394 1'393 1.413 1-422 1.423 1.256 1.283 1.308 P.1 '79 1-79 1-78 1-78 1'79 I *76 1.76 1-74 1'77 1'77 1-75 1 '75 1'74 1-72 1-73 1.71 1-71 1.70 The divergence in P from the value found in stronger solutions is not Any errors introduced by taking Pb * * * 6 as greater than one might expect.206 ON T H E ELECTROCHEMISTRY OF LEAD equal to the total amount of tetrad lead dissolved, and in the value for the active mass of water will be minor ones, but the substitution of (HNOJ4 for {H -)4 must produce a large error. Unfortunately, however, these errors can- not yet be eliminated, but it may be said that the experimental results agree with the theory within the limits of these known errors. The value of P determined within the limits within which the amount of Pb'" was analytic- ally estimated should be the most exact, but all the experiments agree in showing that the tendency Pb....+ Pb * . is one of the largest known. Plumbous Ion Coiaceialratioia i n Vasious Solutions. Further experiments were carried out in the hope that some estimate of 'Ci and C, might be obtained. It may be assumed that in a nitric acid solution in which excess of lead superoxide is present, the plumbic concentration will remain constant, though the plumbous concentration may be altered by alteration cf the amount of salt added. Dilution of the plumbous ion concentration to one-tenth will raise the potential by 0-0295 volt, or, generally, if C, and C, be the two con- centrations of plumbous ions, the difference will be- That the ionic concentrations C, and C, do not vary proportionately with the alteration of the total plumbous concentration, is clearly shown by the, following results.The last column gives the calculated difference if -2 were equal to 2, i.e., if the ratio of the ionic concentrations were equal to the ratio of the total amounts of plumbous salt. C G S S, HN03 normality. - 0.897 0.897 0.897 3'44 3'44 3'44 4-22 422 7'97 7'97 Total Pb.11 grm.-mols. 0'1 0'0 I 0'00 I 0'1 0'0 I 0'000 I 0'0 I 0'0001 0'0 I 0'001 E.1I.F. Rgainst N calomel. 1.256 1*2S3 1.308 1.380 I '394 1,422 1.407 1'444 1.515 1.529 1 Calculated 1 difference. Difference. 0'027 0.025 0.014 0.028 0.03 7 0-0 14 0.029 0'029 0.029 0.059 0.059 0.029 Solubility of Lead Nitrate in Nitric Acid. Incidental observations during the research had proved that lead nitrate was only slightly soluble in nitric acid, so some measurements were made toON THE ELECTROCHEMISTRY OF LEAD taken for analysis.- _ _ _ 20 5 5 207 determine if the solubility varied in a regular manner, and in the hope of information as to how the plumbous ion concentration varied on alteration of the nitrate ion concentration. In some cases the solutions were super- saturated by shaking with excess of lead nitrate at about 28O, before placing in the bath at 25'. . _ _ .~ H NO3 normality. water water 2'02 464 4'64 4'64 8'77 8'77 14.3 5 SoluBility of Lead Nitrate in Nitric Acid at 25'. - ! I c.cs. of Hours at 25O. 170 240 70 130 1 '4 170 2 I0 I12 220 Wt. of PbS04. 9.91 2 2'43 0.8 I 3 1.416 1.125 0.303 0'270 1'120 1'0102 Pb(N03)* grms.per litre. 541 531 178 61.2 61.4 60. j 13.2 14'7 0'536 Pb(N03)~ grm.-rnols. per litre. I '64 1.61 0.185 0.186 0.183 0.040 0'044 0-00 I 7 0.536 Plumbous Ion Concentrations from Potential Measurements. It is, of course, not possible to measure the plumbous ion concentration in nitric acid solutions with a lead electrode, but measurements were made in potassium nitrate solution, as it was thought that the equilibrium would be very similar. S. Labendzinski (loc. cit.) has made a few comparable measure- ments, which are included in the table for comparison. The electrodes used were platinum points plated with lead from a solution of lead acetate and a little acetic acid. When sufficiently coated they were washed with water, and then with a little of solution to be measured, and as quickly as possible placed in the cell and the measurement made.The E.M.F. was found to be at once constant, to remain so for some hours, aiid then slowly fall. In the following tables a is the observed potential when the lead cell was connected with the N calomel cell by a saturated ammonium nitrate solution, b is the potential when the two cells were directly connected with one another, and c are measurements of Labendzinski, comparable with b. E.M.F. of Lead Nitrate Solutions. Lead nitrate grm.-mok. per litre. I '00 0'100 0'010 0'001 E. 11. F. ' nitrate). 1 (dirbect) (Labentdzinski). ei against i 0.412208 ON T H E ELECTROCHEMISTRY OF LEAD ci is the normal potential of plumbous lead, the measure of the tendency Pb**+ metallic lead. The best value is that from the measurement in 0.100 N solution, as it is the result of several concordant experiments, and in more dilute solutions the potential is less steady.The normal potential of plumbous lead at 2 5 O is therefore - 9.137 volt against the hydrogen standard. In the next table are the results obtained when an alkali nitrate was also added to the solution. C, is the concentration of plumbous ions, if the normal potential Pb.*+ metallic lead be 0.137 volt. Pb(N03)z grin-mols. per litre. ._~___ 0'10 0'10 0'10 0'10 0'10 0'10 0'10 0'10 0'10 0'10 Alkali salt grm.-mols. per litre. 0 0.10 KNO, 0.50 KNO, 1-00 KNO, 1.00 (NHJNO, 1-00 NaNO, 2-00 KNO, 3-00 KNO, 5'00 (NH4WO3 10.0 (NH4)N0, E.M.F. _ ~ _ _ _ - i n l b Imm. nitrate).\ (direct). (Labklz.). I 0'449 0'454 0'465 0'478 0'474 0.465 0.490 0'499 0.5 I 2 0.529 0'4.55 ~ 0.460 0.469 0.480 0'479 0.469 0.490 0.498 0.5 I 0 0'529 0'10 0.078 0.030 0.0105 0.015 0.030 0.0042 0-00076 0'002 I 0'00020 Solvent.- Water . . . . . . . . . . . . . . . Nitric acid . . . . . . . . . . . . KNO, . . . . . . . . . . . . . . . _______ Pb(NW2 Normality. ~ grms. per litre. I - ' 536 i 2-02 1 178 Pb(N0313 grm.-mols. per litre. 1-62 I 0'534 It was at first thought that the plumbous ion concentration in nitric acid might be taken as the same as that found in a corresponding strength of an alkali nitrate. I t will be seen, however, that the addition of N sodium, potassium, and ammonium nitrates diminish the Pb- - concentration in widely different degrees. That this difference in the behaviour of sodium and potassium nitrate really exists had already been proved by experiments of Le Blanc and A.A. Noyes (Zeil. physik. Ch. 6, 386), who found that lead nitrate is inore soluble in potassium nitrate solution than in water, but in sodium nitrate solution it was less soluble than in water. Their figures, when considered with the above results, clearly prove that between KNO, and Pb(NO,), there is extensive complex formation, but not so between NaNO, and Pb(NO,),. From the solubility experiments it appears very unlikely that there is any appreciable complex formation between HNO, and Pb(NO,)=, They also determined the freezing points of some solutions.ON THE ELECTROCHEMISTRY OF LEAD 209 but in view of these abnormalities, it seems unsafe to draw any deductions as to the actual plumbous ion concentrations in nitric acid solutions, from experiments with alkaline nitrates.Since both the plumbous and plumbic ionic concentrations remain uncertain, all that can be done is to accept the total concentrations as the nearest estimates at present possible. The two errors will to some extent balance one another, but to what extent cannot be said. If + 1-82 volt against the hydrogen standard be taken as the value for the tendency Pb. - Luther ( Z e i f . Physik. Ch. 3, p. 488 ; 36, p. 385) has shown that if a metal exhibits two valences a and b (higher), and the normal potential for ion a + metal = e,, that of ion b + ion a = e,, and that of ion b --3 metal = e3 + Pb. *, there are several interesting deductions. e3 = X-G -+- (b-y?) e, h For lead, e, = - 0.137 volt, e, = + 1.82 volt, while a and b are 2 and 4, respectively, so that Pb.- * -> metallic lead = + 0.84 volt. Sulphate.-The normal potential P may theoretically be determined with any salt, but, for reasons which have been given, the nitrate is probably the best. A few experiments were made with the sulphate for comparison with the results already quoted. The potential of PbO, in sulphuric acid, ie., of plumbic sulphate, was measured with a platinum electrode, which had been coated with platinum black and lead peroxide, placed in a paste of plumbous sulphate and lead superoxide in acid of known concentration. The E.M.F. was measured against a N calomel electrode with saturated ammonium nitrate as the connecting solution.This was really the measure- ment of the potential on the peroxide plate of an accumulator. E.M.F. against N calomel. 4 H2S04 normality. 7'45 ..' ... ... 1.479 4.82 ... ... ... 1.434 From the method of experiment, the sulphuric acid must have been saturated with plumbous and plumbic lead. No estimation of the solubility of PbO, in H,SO, was made, but an approximation can be arrived at from the results with nitric acid. The equilibrium between lead superoxide and tetrad lead ions must be (Pb... *)(OH')4 = R (PbO,)(H,O)', and K, = (OH')(Ho), where k and K,,, are constants, so that in any solution the amount of Pb. * * varies with H.. In any sulphuric acid solution, then, the amount of Pb.... ions dissolved will be the same as in that of a nitric acid solution of equal hydrogen ion concentration.In this way 3 x I O - ~ grm.-mols. per litre is found as the approximate solubility of plumbic sulphate in 7-45 N sulphuric acid. The amount of lead sulphate dissolved by 29 per cent. sulphuric acid was estimated by Gladstone and Hibbert (Ref. in Dolezalek, Theorie des Bleiaccumulufors) as 0.012 grms. = 0.4 x I O ~ grm.-mols. per litre a t 18". The solubility of plumbous sulphate in 7-45 N acid may be taken as approximately 6x IO-~ grm.-mols. per litre. From these data, P = 1-74 volt against the hydrogen standard, as compared with 1-82 volt, found with the nitrate.210 ON THE ELECTROCHEMISTRY OF LEAD I ‘00 0.0576 0.822 0’539 1.8 x 10-4 0.484 390 x 1 0 4 - 0.82 I 0.538 1-7 x 10-’3 0.484 390 x 1 0 4 I ‘00 0’100 - 0’100 0.0089 0.767 0.767 Proper estimation of the solubilities of lead sulphate and lead super- oxide in sulphuric acid might bring about better agreement, but it is not surprising to find a lower value with the sulphate than with the nitrate, as this is a general phenomenon (e.g., compare Spencer, loc.cit.). Plumbous Ion Coweritration in Alkaline Solution. While working at plumbous ion concentrations, a few experiments were carried out in alkaline solution. Lead monoxide, PbO, is a typical inorganic amplioteric electrolyte. It dissolves in acids to form the ordinary lead salts, and can also behave as an acid anhydride, as with alkaline hydroxides it forms quite a different type of salt. The tendency to act as a basic radicle is much greater than the acid tendency, since it dissolves i n water to a slight extent to form an alkaline solution .The concentration of plumbous ions in alkaline solution may be deter- mined by the electromotive force of the solution with a lead electrode. Pure caustic soda was shaken for some hours with PbO, and lead electrodes were prepared as in previous experiments. Care was taken to prevent the adrnis- sion of atmospheric carbon dioxide, and no unnecessary time was lost in transferring the electrodes to the solution ; but there does not seem to be any special difficulty about the measurement of plumbous potentials, as the same result was obtained in an experiment where nothing more than the usual analytical precautions were taken to exclude atmospheric carbon dioxide, and in a similar experiment in which all vessels were filled with nitrogen, and a stream of nitrogen played on the solution while pouring from the bottle to the measuring vessel. If PbO dissolves in caustic soda accord- ing to the formula- Pb(OH), + N a O H e Na(OH),Pb the equation for the ionic equilibrium will be- Pb(0H); = k (PbO)(OH’). Since the total amount (a) of PbO dissolved must be practically the satne a s Pb(OH)’, this may be written- It is also known that- a = K (PbO)(OH‘). (Pb**)(OH’)” = L (solubility product) and PbO remains constant, so that- a ,/JPb.. = constant (k‘). The following are the results of four independent experiments. tial was measured against a N calomel electrode with direct connection. The poten- 24 x IO- 55 x 10-9 - - PbO dissolved. E.M.F. E.BI.F. nziz&,. I Grm.-mols. I against I against I I k’. per litre. N calomel. N hydrogen. 1 I 1 1 Pb.. 1 k’.ON THE ELECTROCHEMISTRY OF LEAD 211 The difference found in k’ may be due to the non-elimination of the diffu- sion potential. Up to the present no work has been done on the elimination of the diffusion potential at the surface of two liquids, one of which contains hydroxyl ions, The two values for k’ are therefore sufficiently close to support the formula NaPb(OH), for the compound formed when PbO dis- solves in NaOH. Solubility of Lead Monoxide in Water. Some yellow PbO, which had been thoroughly washed, was shaken for several hours with water at 2 5 O , and the Pb.. concentration measured from the potential with a lead electrode. Two concordant experiments gave the E.M.F. against N calomel as 0.614 volt within 0.005 volt. If 0.137 volt against hydrogen be taken as the N pluinbous potential, the concentration of Pb.. in the above solution was 3-8 x IO-~ grrn.-mols. per litre. In conclusion, I have much pleasure in expressing my best thanks to Professor Abegg for his advice and assistance during this research. UNIVERSITY OF BRESLAU.

ISSN:0014-7672    

DOI:10.1039/TF9070200199

出版商:RSC    

年代:1907

数据来源: RSC

摘要:

ON THE ELECTROCHEMISTRY OF LEAD 211 DISC USSI OhT. (Tuesday, December, 11, 1906, DR. T. M. LOWRY i n the Chair.) Mr. N. T. M. Wilsmore said that the author’s work was of considerable interest in connection with the theory of the lead accumulator. Dolezalek‘s theoretical investigations were based in great part on the hypothesis of Liebenow, that lead dioxide gave off bi-valent negative PbOi‘ ions-a some- what unlikely reaction. I t had been shown, however, by Abel that Dolezalek’s results could be reached equally well from Le Blanc’s assumption of the formation of quadrivalent positive Pb * * * ions ; hence the author’s measure- ments niight have further theoretical applications. Mr. H. L. Joly remarked that Prof. J. N. Collie had found a long time ago that oxygen behaved as a tetravalent element in some compounds.He hoped that somebody mathematically inclined would work out the accumulator problem afresh on Dr. Cumming’s new assumption. The Chairman said it would have been a great advantage if the solubility of lead peroxide in sulphuric acid had been determined by experiment rather than by calculation ; such an experiment might easily have been made, whilst the calculation could only lead to very uncertain results. Dr. A. C. Cumming (communicated) : The theory for the accumulator on the assumption of tetrad lead has been worked out mathematically by Abel (Zeit.fiir EZectroch. 7, p. 731). Dr. Lowry is of opinion that the estimation of the solubility of PbOe in sulphuric acid is an easy matter. Obviously no precipitation method could be used, so that one must evaporate the solution and weigh the lead sulphate. The evaporation of half a litre of 7 or 8 N sulphuric acid to obtain a few milligrams of lead sulphate is a process which requires much time and attention. I had hoped to have estimated this solubility experimentally, but a few experiments convinced me that it would require more time than I could give.I t seemed better, there- fore, to give a calculated value, which did not profess to be more than an approximation, than to do a hurried experiment. Since the reading of this paper, a research by Dolezalek and Finckh (Zed anorg. Ch. 51, 1906, p. 3201, has appeared on the same subject. Their investigation was carried out with I cannot agree with him at all.212 ON THE ELECTROCHEMISTRY OF LEAD solutions in sulphuric acid, and it may be meiitioiied that they regard the estimation of PbO, in sulphuric acid of less than z o N as impracticable. I t may be of some interest to compare their results with my calculation. The calculation led to the value -3 niilligrm. molecules per litre in 7.5 N sulphuric acid. The most dilute solution in which they were able to analytically estimate the PbO, was 20.7 N, which dissolved 1.8 millimols per litre, so that the value obtained by calculation was of the right order of magnitude, and nothing more was claimed for it. The experiments with sulphuric acid were, however, only an incidental part of the research, since I was mainly concerned with the determination of the value for Pb * - - * -> Pb * *. The mean value found was 1-83 volt, and it is satisfactory to notice that, working with the sulphate, Dolezalek and Finckh obtained values varying between 1.8j and 1-90 volt.

ISSN:0014-7672    

DOI:10.1039/TF9070200211

出版商:RSC    

年代:1907

数据来源: RSC

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CONTRIBUTIONS TO THE STUDY OF STRONG ELECTROLYTES. I. THE ELIMINATION OF POTENTIAL DUE TO LIQUID CONTACT. 11. THE POTENTIALS OF SILVER NITRATE SOLUTIONS. By ALEXANDER CHARLES CUMMING, D.Sc. (1851 Exhibition Research Scholar).‘k ( A Paper read before the Faraday Society on Tuesday, December 11, 1906, DR. T. M. LOWRY in the Chair.) I. THE ELIMINATION OF POTENTIAL DUE TO LIQUID CONTACT. It has been a constant source of difficulty in electromotive force measure- ments that, in addition to the electromotive forces between the electrodes and the solutions, there is another source of potential at the surface of contact of the two solutions one wishes to compare. Any actual measurement is the sum of these two, and to obtain one separately is not always easy. Planck (Wied. Ann. 40, p.561, 1890) has shown how the E.M.F. due to the contact of two dissimilar dilute solutions may be calculated if the composition and ionic con- centrations are approximately known. In practical work the data required for Planck‘s formula are often unavailable, and in any case the calculation is a most laborious one. Tower (Zeit. physik. Chem. 20, p. 198) showed that if two solutions were connected by a potassium chloride solution, the (‘ diffusion” E.M.F. was materially lowered, and, following a suggestion in Luther Ostwald’s book, it has become customary to use a N or a saturated potassium chloride solution, and to assume that the diffusion E.M.F. is thereby eliminated, so that the observed E.M.F. is solely from the electrode potentials. It may be readily proved that this is not quite accurate.If it is permissible to add a neutral salt to both solutions the diffusion potential is eliminated (Sackur, Zeit. physik. Chem. 38, p. 129), but such addition of salt naturally alters the ionisation cf the salts already there, and this cannot always be allowed for. N. Bjerrum (Zeit. physik. Chem. 53, p. 428) has recently investigated the effect of joining solutions with different concentrations of H ions by various strengths of potassium chloride solutions. He found that a saturated potassium chloride solution did not remove all the diffusion potential, but deduced an empirical rule that the amount of diffusion potential still un- removed was equal to the difference in the E.M.F. with saturated and with half-saturated potassium chloride as the connecting solutions.The reason for taking this particular correction is not clear, but for solutions containing H ions it appears to be satisfactory over the range of concentrations investigated by Bjerrum. In the course of another research this question of the elimination of diffusion potential was of importance, and a systematic attempt was made to * Communicated by N. T. M. WILSMORE, M.Sc. N 2’3214 CONTRIBUTIONS TO THE STUDY find the best method. The various methods were tried for two extreme cases, in one of which the anion was very much faster than the cation, and in the other the cation velocity was much the greater. In one set the system measured was the following :- Hg . Hg,Cl, I! HC1= C, X = C, HCl= C, Hg,CI, . Hg where C, = N, C, = - and X was any desired solution of known concentra- tion C,.The special case where X was onitted and the two solutions directly connected may be first considered. For the simple case of two solutions of the same substance, but of different concentrations, the electrode E.M.F. is giverl by the equation (Nernst, Zed. fhysik. Chem. 4, p. 129) :- (I II I1 N 10' where C, and C, are the ionic concentrations. The value of- RT - - log'' at 25' = 0'0591 Volt. F ' log, - The ratio 5 may be obtained from the conductivities, and the calculated electrode E.M.F. = 0.0563 volt. This calculation is made on the assumption that the influence of the calomel is the same in both cases, so that it may be neglected. This may not be quite correct, but, for present purposes, a small error from this source is of little importance.The diffusion E.M.F. between two solutions of the same substance, b u t of different concentrations, may be calculated from the formula- c, U - v RT c r t x v F C, e d = - - , - . log 2 where u and v are the ionic velocities. The values given by Ostwald for H and C1 are 347 and 75 respectively, so that- ed = 0.0381 volt. The mean experimental value from a number of readings with the two cells in direct connection was 0.0950 volt. Subtracting the calculated diffusion E.M.F. we have for the system- Hg I/ HgzC1, /I HC1= I HCI = . I Hg,Cl I/ il a ll Hg e = 0.0950 - 0.0381 = 0.0569 volt, as against the calculated value of 0.0563 volt. As a standard value against which to compare the later results, the E.M.F. was taken as 0.057 volt to within a millivolt. The results when the two cells were joined by various alt solutions may now be given.Since chlorides cannot always be used nitrates were tried CONNECTING SOLUTION. E.M.F. . . . . . . . . . . . . . . . Direct connection 0.0950 N Potassium nitrate . . . . . . . . . . . . . . . 0.0760 3 N ,, ,, (saturated) . . . . . . . . . 0.0683 With the saturated solution there was still a large amount, 0.011 volt, of diffusion potential not removed. Ammonium nitrate gave similar values with like concentrations, but in this case much stronger solutions could be used.OF STRONG ELECTROLYTES 21 5 CONNECTING SOLUTION. Direct connection . . . . . . . . . . . . . . . Ammonium nitrate . . . . . . . . . . . . 4 N 1 N 9 , 5 N 9 ) I O N ,, Saturated ammonium nitrate .. . . . . . . . )) 2 ) . . . . . . . . . . . . - 2 )) ,) )) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Correct value = 0.057. E.M.F. 0*0950 0.0848 0.0800 0.061 7 0.0566 0.0565 0'0740 To prove that the diffusion E.M.F. depends only on the strength of the solutions at the surface of contact, the following system was measured- The E.M.F. found was the same as that of the system- Though there is little experimental evidence on the subject, the principle underlying the use of potassium chloride as a connecting solution is that a salt which is to be of use for this purpose, must have an anion and a cation, which possess, as nearly as possible, equal velocities. That this is really a requisite condition may be readily shown, e.g., by the use of sodium nitrate or lithium chloride solutions.CONNECTING SOLUTION. E.M.F. Direct connection . . . . . . . . . . . . . . . 0.0950 N - lithium chloride . . . . . . . . . . . . . . . 0.0880 ), . . . . . . . . . . . . . . . 0-0682 N 1 ) ) , . . . . . . . . . . . . . . . 0.0464 4 N )) 8 N ,) 8 N Sodium nitrate . . . . . . . . . . . . . . . 0.0570 Saturated sodium nitrate . . . . . . . . . . . . 0.043 2 I 0 . . . . . . . . . . . . . . . . 2 N ,, , O"574 ,) . . . . . . . . . . . . . . . 0.0330 There is no sign in this case of a constant value being obtained with in- crease in the concentration, and the agreement of two of the above results with the correct value, 0.057 volt, is evidently fortuitous. A similar set of experiments was next carried out with solutions of a different type, in which the diffusion E.M.F.was in the reverse direction to the above. The two cells were N and -- lithium chloride solutions, each with a Hg 11 Hg,Cl, electrode. When the cells were directly connected the observed E.M.F. was 00361 volt. The diffusion potential calculated from the conductivities =0*0169 volt, and adding this to the observed value we have for the electrode E.M.F., e = 0.0530 volt. When the E.M.F. is calculated in the same manner as in the previous N I 02 16 CONTRIBUTIONS TO T H E STUDY E.M.F. BETWEEN N. AND Y f o HYDROCMORIC AciD. HYDROCHLORIC AciD -3------ ----- D I e 3 4 5 6 7 ti 7 IO II 1 2 1 3 rq STRENGTH OF CONNECTING SOLUTION. experiment, with the conductivities as a measure of C, and C,, the value.calculated is 0'0522 volt. The results with various connecting solutions may now be given. CONNECTING SOLUTION. E.M.F. Direct connection . . . . . . . . . . . . . . . 0.0361 N ammonium nitrate . . . . . . . . . . . . 0.0480 0.0532 5 N ?7 I O N ?, ,, 0.0543 Saturated potassium nitrate . . . . . . . . . . . . 0'0502 Saturated potassium chloride . . . . . . . . . 0.0515 J , . . . . . . . . . . . . . . . . . . . . . . . . Strong solutions of ammonium nitrate proved so satisfactory for both HC1 and Li Cl solutions, that it seems probable that a strong ammonium nitrate solution will be found generally useful for the elimination of diffusion potential, particularly when the electrode solutions are concentrated, as the connecting solution should always be much more concentrated than the solutions to be measured.The comparatively great solubility of ammonium nitrate makes it, there-OF STRONG ELECTROLYTES 217 fore, preferable to potassium chloride when the electrode solutions are strong. The following observation is not directly connected with the above experiments, but is of some interest in itself. N When the N and - HCI cells were connected by means of a hydrochloric acid solution of some other concentration, it was found that the E.M.F. remained the same, though the strength of the connecting solution was varied from - up to the most concentrated acid. I have not been able to find any reference to a similar observation, but it may be readily shown to follow from Nernst’s theory. The E.M.F. between two solutions of the same substance, but of different ionic concentrations, C, and C,, is given by the formula- I 0 N I00 If, in the case we are considering, C, and C, be the concentrations in the two cells, and C, that of the connecting solution, the diffusion potential between one cell and the connecting solution is- ?2.PT . log c, u + v F c4 and between the other cell and the connecting solution, The resultant diffusion potential is the difference between these- or the same as with direct contact, whatever the value of C, may be. This, of course, applies to any two cells joined by a solution of the same substance. In addition to the experiments with the hydrochloric acid cells, it was proved to be true for the pair of lithium chloride cells used in the above experiments.With direct connection, or when joined by a lithium chloride N solution of any concentration from - up to SN, the observed E.M.F. remained the same. 1 0 11. THE POTENTIALS OF SILVER NITRATE SOLUTIONS. It is well known that the Ostwald dilution law, which holds so well for weak electrolytes in aqueous solutions, finds an apparent exception in the case of strong electrolytes ; in other words, the alteration in the proportion of ionised to unionised substance with dilution is not in accord with the law of mass action, if we take the conductivity as a measure of the amount ionised. This has been a fruitful source of experiment and discussion, and in the following research an attempt was made to obtain some fresh information on one of the disputed points. While many accept the conductivity as a measure of the ionisation, others, and notably Jahn, believe that in strong solutions the conductivity yields too high an estimate, i.e., that the degree of dissociation is less than L.PCc Jahn (Zeit. physik. Chew. 33, p. 370) has measured the ionic concentrations2 18 CONTRIBUTIONS TO THE STUDY of potassium chloride and other salts by means of electromotive force measure- ments, and according to his results the substances examined obey the dilution law in very dilute solution. The following experiments with silver nitrate were undertaken in the hope that further information in this direction might be obtained. Silver nitrate is readily obtained pure ; it can be measured with pure silver rods as electrodes, and thus eliminate any possibility of error from the use of a depolariser, such as calomel, which must, even if only to a small extent, go into solution ; and finally it possesses the advantage that its two monad ions have almost identical velocities, so that the correction for diffusion potential is very small.ExferimentaZ.-All measurements were made in a thermostat at 25O. The E.M.F. was determined by the Poggendorff compensation method with a DArsonval galvanometer, or, in the case of solutions below -, a Lippman electrometer as zero instrument. One set was made by electrically coating platinum wires with silver from a potassium silver cyanide solution. Another set was made in the same manner with a solution of silver chloride in strong hydrochloric acid, while the third set were pure silver wires obtained from Herzus.At first these wires were sealed into tubes with fusible glass, and the junction covered with a layer of asphalt, and then with paraffin. It was found, however, that the contact between the silver and the cover was never perfect, but always introduced errors, while plain uncovered silver rods answered the purposc excellently. These rods were always cleaned before use with ammonia, dilute nitric acid, and then water, and were found to give no difference of potential in a - silver nitrate solution. At least two electrodes were used in each cell, and as it was found that the E.M.F. was the same with all three kinds of electrodes, the silver rods were generally employed, as they were the most convenient. ?!- Silver Nitrate.-With the solutions in direct connection with one N I00 The silver electrodes were prepared in three different ways. N I0 I 0 I00 another a number of experiments were made.N Example: Two silver rods (AI and A2) served as electrodes in the - All four rods had I 0 N solution, and two others (BI and B2) in the - solution. I 0 0 N been cleaned just before use and tested against one another in - silver nitrate. I0 AI against BI =0-0588 volt. A2 ,, BI =o'o5y1 ,, AI ,, B2=0*0;91 ,, A2 ,, R2=0'0590 ,, Mean = 0'0590 ,, Three other similar experiments gave the following mean values :- 0.0591, 0.0589, 0-0587 volt. In some other experiments, in which the number of electrodes or some small detail in the method of measurement was altered, the results were as follows :- 0.0591, 0'0592, 0.0588, 0.0591, 0'0590, 0.0589.OF STRONG ELECTROLYTES Platinum points plated with silver from a solution of silver chloride in strong hydrochloric acid were next used as electrodes. E.M.F.= o*osgo 0'05go volt. ln each cell two electrodes were next tried, one (AI) a silver rod and the other (Az) a platinum point plated with silver from a potassium silver cyanide solution. In the other cell were a similar pair of electrodes, BI and Bz respectively. AI against BI =0*0593 volt AI ,, B2=0'0590 ,, A2 ,, BI =0-0590 ,, A2 ,, Bz =0'0591 ,, N N The mean value for all the measurements of - against - silver nitrate was 0-05cp volt. When the diffusion E.M.F. was eliminated by connecting the two cells by a I O N ammonium nitrate solution, the mean value for the E.M.F.was 0.0556 volt. SimiIarly with saturated potassium nitrate as the connecting solution the mean E.M.F. was 0.0555 volt. Nernst (Zeit. fhysik. Chem. 4, p. 129) has given the formula for the diffusion potential between two strengths of the same solution as- I 0 I 0 0 From Ostwald's figures u at 2 5 O = 71-0, and v = 63.0. The conductivities of Lob and Nernst (Zeit. physik. Chem. 2, p. 948) may be taken as a measure of C, and C,, so that- 8 x 0'0591 x log,o- 1'003 ed= - I34 0.1217 =0'0033 Volt. Even if it be not quite correct to take the conductivities as a measure of C, and C,, the ionic concentrations, it must be near enough to the truth for the calculation of this small correction. N N We have now the E.M.F. of - . - silver nitrate by three methods, the difference being due to the different methods for the elimination of the diffusion potential.I 0 I 0 0 ELIMINATION OF DIFFUSION POTENTIAL. E.M.F. By calculation . . . . . . . . . . . . . . . . . . 0.0556 By ammonium nitrate . . . . . . . . . . . . 0.0556 By saturated potassium nitrate . . . . . . . . . 0.0555 Nernst in his fundamental paper gave the formula for the E.M.F. between two solutions of the same kind as- and suggested the conductivities as a measure of C, and C,. If we calculate the value of e from the conductivities of silver nitrate in - I 0 and - I 0 0 solution, we obtain e = 0.0557 volt. N N220 CONTRIBUTIONS TO THE STUDY The close agreement between this value and that found experimentally proves that the ionic concentrations as measured by the conductivity and by E.M.F.measurements are the same, or at least in the same ratio. Special attention must be directed to this, as it accords with the view of Ostwald and Arrhenius that the conductivity yields a true measure of the ionic concentra- tion, in contradistinction to the results of Jahn (Zoc. cit.). Some other strengths of solution were also measured, but not in so much detail as the pair given above. N - against -!!- Silver Nitrate.-The electrodes used were silver rods. I00 1 ,- The potential in all cases where a solution below -was used was badly defined and hard to measure. Six experiments, in each case with two electrodes in each cell, were made with the solutions directly connected. The mean values were as follows :- N I00 0'0612 0'0620 0.0618 0.06 I5 0'0622 0.0618 mean = om618 volt. Calculated diffusion potential = 0.0038 volt, so minus dffusion potential Six similar separate experiments, but with elimination of diffusion potential E.M.F. = 0.580 volt. by 10 N ammonium nitrate solution- 0'0577 0'0579 0'0577 0.0591 0.0578 0'0579 mean = 0.0579 volt. The E.M.F. calculated from Nernst's equation with the conductivities as a measure of C, and C, = 0.0580 volt. N against - Silver Nitrate.- I 0 Mean E.M.F. with direct connection = 0.0312 volt. Calculated diffusion potential = o*oozz e = 0*0290 With elimination of diffusion potential- (a) by ammonium nitrate = 0.0286 ( b ) by saturated potassium nitrate = 0*0290. The E.M.F. calculated from Nernst's equation and the conductivities is 0.0292 volt. Conclusion.-The deduction from these experiments is that for silver nitrate the electromotive forces of its solutions are such as to support the belief that the conductivity gives a true measure of the ionic concentration. A. A. Noyes (Technological Quarterly, 1904, 17, p. 293), from a review of the experimental data on the subject, regards this as generally true for strong electrolytes, and it may be pointed out that the experiments in the first part of this Paper with hydrochloric acid and lithium chloride cells also support this view. It is with great pleasure that I take this opportunity to thank Professor Abegg for his kind assistance during the progress of this research. UNIVERSITY OF BRESLAU.

ISSN:0014-7672    

DOI:10.1039/TF9070200213

出版商:RSC    

年代:1907

数据来源: RSC

摘要:

OF STRONG ELECTROLYTES 221 DISCUSSION. Mr. N. T. M. Wilsmore welcomed Dr. Cumming’s work as an important advance towards the correct measurement of electrode potentials. There were more difficulties in the use of Planck’s formula than had been mentioned. Planck himself had pointed out that the formula held good only when ionisa- tion was practically complete in both solutions, and when all the ions present had the same valency. Dr. Cumming’s method appeared to be entirely successful in eliminating contact potential between different solutions, thus allowing the electrode voltages to be measured directly. The Chairman said as regards Jahn’s work on strong solutions, the conductivity could not be relied on as an exact measure of ionisation for con- centrations exceeding - The expression ‘( strong solution ” was a relative one ; at one time a 5 per cent. solution would have been called dilute. One of the chief factors to be considered was viscosity. This was generally appreciably greater in a - solution than in pure water. Silver nitrate solu- tions were not very viscous and the conductivity method of determining ionisation might be applied to somewhat stronger solutions than in the case of certain other salts. N I00 N I 0

ISSN:0014-7672    

DOI:10.1039/TF9070200221

出版商:RSC    

年代:1907

数据来源: RSC

摘要:

STORAGE BATTERIES AND THEIR ELECTROLYTES. By R. W. VICAREY, Member of the American Electrochemical Society. ( A Paper read before the Faraday Society on Tzmday, Dccember 11, 1906, In July, 1905, I submitted a Paper to this Society, intended as a rtsumt of a subject of a most important and interesting nature, entitled ‘( Storage Batteries and their Electrolytes.” That Paper may now be considered as an introductory one to this and subsequent Papers that I propose to submit as soon as leisure will permit me to arrange and tabulate my collection of data and experience. It has given me the greatest pleasure to note how much attention has been given to my Paper of July by those directly and indirectly connected with storage batteries, and it will encourage me to avail myself of every opportunity that may occur from time to time to complete the proposed series of Papers.It is my intention to divide the subject into four separate sections, i e . - DH. T M. LOWRY in tlzc Chair.) I . The Manufacture and Works. 2. The Acids used. 3. The User of the Battery. 4. The Water used as Diluent. Seeing great difficulty in the production of an ideal battery without the co-operation of these four departments, I consider it advisable j o make the above four divisions. I. MANUFACTURE. Until very recently the manufacture of the storage battery plate was carried out in most works by rule of thumb. In other words, no definite quantitative results were aimed at, and as soon as the original inventor of the process had completed his laboratory experiments and handed them over to be reproduced on a large scale in practice, then began troubles and unforeseen irregularities, This condition of affairs very naturally resulted in introducing modifications or slight alterations of the original process in such a way that great differences of opinion occurred even between those who should have known most about the processes, and it soon became common for every storage battery maker to have his own particular secrets of manufacture, even when two or more makers were adopting the same original process.But science has been making grcat strides, and side by side with it the keen competition of commerce has brought makers to realise the necessity of producing the most serviceable article at the least possible cost. This has brought the storage battery industry to such a state of uniformity that a comparison of price lists of the principal makers shows that there is very little to choose between them.The following table has been compiled from the latest complete lists that I have been supplied with, and I would call your attention to the remarkable uniformity which is apparent throughout, 222Type. I Maker. E.P.S. E pstei 11 A.B.P. Tudor Tudor E ps tein Hart ... D.P.Co. A.B.P. A.B.P. E.P.S. ... ... ... ... ... ... 6 . . ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... Pritchett and Gold ... Epstein . . . . . . Hart . . . . . . . . . E.P.S. . . . . . . Hart . . . . . . . . . Pflugen . . . . . . ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ...... ... ... ... ... ... ... ... ... ... ... ... ... ... ... P A C.S. H.E. L.E. B C.S. S.A. S.O. s. w. W.S. - C AL L AT P TABLE I. Cornjarison of Price Lists, 1902. Whether including Accessories No No Yes Yes Yes No Yes No Yes Yes No No No Yes No Yes No Cost in Shillings per Plate Complete. I 2.83 12'00 12-00 9'33 9'33 7-83 6.00 6.66 6'33 6.3 I 5'90 5'83 5'83 4'52 3 '92 3'43 1.86 Cost in Shillings per lh. of Cell Complete. ___~.____._ 0'350 0'444 0.378 0.583 0.583 0.566 0.240 0'384 0'440 0'434 0'327 0.232 0.614 0.285 0.387 0.686 0.516 Cost in Shillings per Ampere Hour Capacity. 0.275 0.308 0.171 0.622 0.622 0'349 0'200 0'3'7 0.27 I o 198 0.263 0.267 0'353 0.227 0'21 I 0.38 I 0.1614 Cost in Shillings per lb. of Plates only. .- ? 0'837 0.625 1.076 1.076 I '04.4 ? ? 0.863 0'798 ? ? 1.166 ? ? ? 0'775 Lbs.per Ampere Hour of Cell Complete. 0.785 0.692 0'453 1.066 0.800 0.615 0.833 0.825 0.615 0'457 0.803 1.088 0'579 0'797 0.546 0'555 0'333 Ampere Hours per lb. of Cell Complete. 1,272 1.444 2-185 0'937 1.250 I -626 1'200 1-21 I 1.627 2.186 I '244 0.919 1.938 1.253 1.830 1.800 3.000224 STORAGE BATTERIES AND THEIR ELECTROLYTES whether as regards specified capacity at a given price, weights of cells for a given capacity, or the number of plates per cell for a given output. Thus possibly a Plant; type of cell may contain, say, seven plates, while a Faur6 of the same output will contain eleven or perhaps thirteen plates, yet in all probability each of these cells will be found to occupy approximately the same volume. Nevertheless I am of opinion that there is much room left for improve- ment by the manufacturer.It is true that he is dependent upon, and, in a large measure, entirely in the hands of the user, according to the manner in which the latter handles his batteries ; but it should pay the manufacturer to make more stringent systems, and not place too much reliance on the maintenance system. I t is not generally known what a large amount of incidental expenses occurs in the manufacture of accumulators, and this is to a great extent why some companies have had so short a life. Experimental work is very expen- sive, and even a very small capacity test with one cell of IOO ampere-hours’ capacity will quickly run into hundreds of pounds. The result is, information on many points is scarce and valuable, for few, even when having every facility, care to commence experimental work that may end one knows not where.I think it may be of interest if I give a few of the experiences that one may expect to meet with if one contemplates experimenting in a commercial or practical manner. We may take as an example the nickel cell adopted by Edison. As a rule, in a new works, probably no troubles will be experienced for some considerable time. But after a time, for no apparent reason, and without any warning, it becomes an impossibility to continue successfully. I have been unfortunate enough to have had some experience in nickel accumu- lator experiments, and I am not at all sure that the Edison cell will not be found in practice to be as erratic and peculiar as the lead cell of the present day.As regards the lead cell, it is needless to point out how troublesome lead is to manipulate in electrochemical work. Until very recently it had not even been possible to deposit it satisfactorily, although after all these years there seems to be hope of this at least being accomplished. In our imaginary new works the manufacturer will start with new material and new plant, and the results obtained may be fairly uniform, and possibly troubles even unknown. But, unfortunately, the use of such things as lead salts, sulphuric acid, and the innumerable materials that go to make up the manufactured article, must in time introduce impurities, and these will exhibit themselves in one of two places, either in the manufactured article, or in and about the plant at the works, or possibly in both places.Such unknown quantities as here referred to are generally due to buying at the cheapest rate, failing to ascertain the quality of chemicals bought by analysis, or endeavouring to economise unwisely. These are things that the manufacturer can guard himself against. But there are other and more far-reaching uncertainties that he has to face, namely, those caused by the carelessness of employis. For instance, a works may be newly equipped from top to bottom, and all may be going well, when incidents such as the following, many of which I have seen personally, may occur : (I) A carpenter repairing an acid tank will drop a brass screw into the acid and leave it to tell its own tale by depositing on the plates or dummies ; (2) a labourer will carry acid in iron pails ; (3) a labourer will empty one acid into a tank of different acid ; (4) a labourer will sweep up the floor of the casting shops and empty his sweepings into the metal pot containing pure metal ; (5) a wireman will file, solder, or repair cable leadsSTORAGE BATTERIES AND THEIR ELECTROLYTES 225 over cells or acid tanks ; (6) the dropping of such things as nuts, bolts, pliers, spanners, &c., in a cell and leaving them there, finally pumping the acid from that cell with that from others into the large mixing tank ; (7) the putting of wet plates on dirty floors or leaving them exposed to rain and weather ; (8) breakdowns of engines and dynamos in the middle of important processes, necessitating possibly the scrapping of several hundred plates ; (9) insufficient formations ; (10) the use of bad water.These and similar almost unavoidable occurrences are some of the troubles that a manufacturer has to face. The ideal accumulator works should be erected on carefully chosen ground away from all manufacturing centres, i.e., as far in the open country as railway facilities for transport of goods, in and out, will permit. Brick or elaborate and expensive buildings are not necessary ; they should, in fact, be specially avoided, as their deterioration and cost of maintenance amount to a considerable figure per annum owing to the effects of the acid fumes. Nothing is more satisfactory than sheds constructed simply of new and clean wood. As the product has to pass through several separate and different pro- cesses, it is very essential that each process be carried out in separately- constructed shops, or rooms, thereby preventing any interference of one process with another.It will be gathered from my previous Paper that ammonia plays a very important part in accunlulator practice by causing irregularities both in the works and also on the installation, although the extent to which ammonia affects the storage battery has yet to be thoroughly investigated. It may be stated, however, that nitrogen, combined with either oxygen or hydrogen, must always be looked upon as a subtle enemy, Now several processes of manufacture, both chemical and electrochemical, make use of nitrogen in the preliminary treatment of the plates, in the shape of nitric acid, nitrate salts, or nitric peroxide, and the nitrogen invariably remains in the plates to be dealt with subsequently, usually in a sulphuric acid bath of various densities.Nitrogen appears to be capable of repeated and unlimited oxidation and reduction ; for instance, if we have a sulphuric acid solution and add to it known quantities of nitrates or nitric acid under certain conditions the current may reduce the whole of the nitrogen compound present to ammonia, which, of course, combines with the sulphuric acid to form ammonium sulphate. On the other hand, under different conditions the nitrogen may be oxidised to nitrite, and subsequently to nitric acid. These compounds each have their respective characteristics and they each appear at their respective places, ammonia at the negative or spongy plate, and the nitric acid or nitrates at the positive or peroxide plate.The most striking effect appears to be, in the case of ammonia, a serious loss of original capacity in the negatives ; and in the case of the nitrates, an excessive growth of the positives, with disastrous results. It may be thought by some that both effects would appear simultaneously, seeing that the nitrogen is capable of undergoing alternately oxidation and reduction. It unfortunately does not so happen in practice for some reason not yet ascertained. Here, then, we have two very important things of the utmost concern to the manufacturer. In the majority of cases the maker has no control over the methods adopted by the users in handling his battery, and therefore it becomes a very delicate matter to decide whether such impurity has been introduced since the battery left the maker or was originally there before it left his hands.It should be mentioned in passing that nitrogen in the form of ammonia, or oxides, is very common in most waters and in most atmo-226 STORAGE BATTERIES AND THEIR ELECTROLYTES spheres, and therefore can easily be introduced into the cells in ignorance by the user, notwithstanding that the maker has handed over a battery perfectly free from the nitrogen impurities used in the manufacture. Returning to the manufacturer, it might be urged, why use nitrogen com- pounds at all, seeing the possible dangers its non-elimination can lead to. But it must be remembered that this element is the best agent we have for assist- ing in the oxidising process of the positives; and that it has also the very attractive property of causing the plates to acquire a good rich colour, besides effecting economy in production. In the works the troubles mostly experienced are due to ammonia, which of a necessity is almost sure to exist, and cases have come under the writer's notice where newly-made plates have shown considerable loss of capacity due to this. There is a popular idea that a treatment of the plates in a bath of ammonium sulphate eliminates all nitrogen impurities, and it has been put into practice by many makers.According to the late Desmond Fitzgerald : "When, by the protosulphate of iron test or otherwise, the presence of an oxide of nitrogen, say, nitrous anhydride (N,O,), is detected, the acid may be purified by adding to it sulphate of ammonia, and heating until it fumes strongly and ceases to give off any gas.The oxide of nitrogen is thus decomposed and its nitrogen evolved, according to the following equation : I n the same manner nitric acid is completely eliminated. zHNO, + z (NH,),SO, = 2H,S04 + 7H,O + 6N, and this equation is applicable to the following suggested process for getting rid of nitric acid in plates treated by nitric acid as described at the com- mencement of this section, viz., saturate the plates with a weak solution of sulphate of ainmonia and heat to 6000 F. The fusing point of lead is higher than this, viz., 618.8" F." But the vital point remains, is it practical ? To this I must answer that few accumulator works have the necessary facilities to carry the work out as I believe was intended by Fitzgerald.For instance, he says, "saturate the plates with a weak solution of ammonium sulphate and heat to Goo0 F." Now this would imply that the plates are to be dipped, or better immersed, in a solution of ammonium sulphate for a sufficient time to become saturated, after which they are to be taken out of the bath and heated to 600" F. To obtain 600" F., when the melting-point of lead is only about 619" F., requires very delicate adjust- ment and not only careful but skilful handling, and such work, I think, can only be done satisfactorily in a muffled furnace. I know of a manufacturing works, which, suffering from nitric acid troubles, adopted Fitzgerald's sug- gestion, as follows : They immersed their plates in the ammonium sulphate bath and heated the bath up to as high a temperature as possible (which was only 2 1 2 O F.) for a prolonged period, the plates were then taken out and placed in adrying room for a period of some thirty odd hours, the temperature of the drying room bcing maintained at 100" F.Now we see how true is the adage, "What is food for one is poison for another." What Fitzgerald referred to was found by himself to be success- All this is perfectly true from a chemical standpoint.STORAGE BATTERIES AND THEIR ELECTROLYTES 227 ful, but was no doubt specially applicable to the manufacture of his lithanode plate. He himself says on p. 159 of “The Lead Storage Battery” : (( It was found necessary to expel the whole of the ammonia from the plates, by heat if the period of seasoning was insufficient, prior to painting with peroxide, otherwise the latter was liable to become decomposed with production of a nitrate according to the equation : 3PbO, + 2NH3= NH,NO, + H,O + 2PbO.” Here we have pointed out the danger of the presence of ammonia, yet we find a manufacturer adopting Fitzgeralds suggestions in such a way as actually to introduce more nitrogen impurity than originally was present.Can anything more clearly illustrate how dangerous it is to use other people’s advice or suggestions without due consideration as to their applicability. Needless to say the case quoted involved a loss of many thousands of pounds.As before stated, many makers use nitrogen in some form or other in their processes, and I again say, in view of the advantages gained, they are justified and correct in doing so, but it is absolutely imperative that they adopt means by which they can ensure its total elimination before the plates are considered finished and out of their control. This, no doubt, means a very great deal to those makers who make a practice of partially forming the plates in the works and completing the process when erected in situ, but if nitrogen is used at all the difficulties must be met. It will be of interest to give some of the peculiar experiences to be met with in works, and directly traceable to nitrogen, although accelerated more or less by other impurities, in the first place dealing with works whose practice it is to complete their process and make capacity tests before despatch.Here it has sometimes been found that whole batches of plates have failed to the extent of some 10 to 20 per cent. of their listed capacity in a sudden and unaccountable manner. I know an extreme case in which instead of giving a six hours’ discharge at normal rate the cells gave out in twenty minutes. This, which appeared on the first test after the formation process, was repeated at intervals with many batches of newly-made plates, and after much experimental work was capable of being attributed to the presence of nitrogen compounds. Another common experience again attributed to nitrogen is that of an unusual fall in sp. gr. during discharge, with failure to rise correspondingly in the succeeding charge.For example, given a battery designed on correct lines in respect of quantity of active material, correct spacing between plates, theoretical volume of working electrolyte, and proper sp. gr., under ordinary atmospheric conditions, and suppose it discharged at a normal rate lasting, say, six hours, then if the density at start be 1’200 at 60’ F., then at the finish, correcting for temperature, the density should be about 1.170; or if it be 1.220 at the start, it should be 1.190 at the finish, these figures on the average applying to any type and size of cell at present on the market. But it some- times happens that instead of a fall in sp. gr. of 0.030 something like 0.060 is experienced, and I have at the present moment in my laboratory two cells whose fall has been 0.119 and 0.121 respectively, being the greatest fall I have ever known, and this occurring without any visible changes being observed.Now, in practice many people charge until a fixed density has been attained, and in such cases we invariably are informed that the charge required in ampere-hours is something like 20 to 50 per cent. in excess of the discharge taken out in ampere-hours, obviously an uneconomical procedure228 STORAGE BATTERIES AND THEIR ELECTROLYTES for the owner. On the other hand, many people control their charge by making it a fixed percentage of perhaps 10 to 15 per cent. in excess of the pre- ceding discharge, and in these cases a systematic decrease in sp. gr. is often experienced. These results, indirectly traceable as a rule to nitrogen impuri- ties, are equally deleterious to the welfare of the batteries ; in the first case causing systematic overcharging, with the shedding of much active material, and in the second case systematical undercharging and much expansion due to sulphating, buckling, and so forth.Dealing now with works whose practice it is to complete their processes in situ, the same experiences will be met with as before mentioned, but they are the cause of even more anxiety than if met with in the works. In any case greater risks are run by those adopting this system, because of local conditions over which the maker has no control, such, for example, (I) as the presence of harmful neighbouring works, (2) low charging current available, preventing the formation being carried out at its proper current density, (3) unforeseen stopping of the charging current, (4) the quality of the water used as diluent, &c., &c.Finally we have to consider works that deliberately use nitrogen compounds, and here the following experiences are met with, in addition to those cited above: (I) A very excessive shedding of PbO, appearing periodically ; ( 2 ) an abnormal heating of the forming electrolyte, that is to say, if the average forming temperature is 25 to 30" C., it may suddenly at critical points run up to as much as IOOO C., and in cases where glass boxes are used, cause them to break and so stop the formation ; (3) heavy deposits of spongy lead, generally on one side of the negative plate or dummies, sometimes on both, such deposit being sufficient actually to bridge across to the opposite plate and cause short circuits so rapidly as to need a man's whole time to remove them during the single formation ; (4) abnormal growth or expansion of the positives during formation.For example, a serrated lead plate, 12 in. x 12 in,, and weighing 20 lbs. to the square foot, should grow, horizontally and vertically, not more than 0.375 in. when formed by a Plant6 method. Anything exceeding this growth should be considered abnormal, and its cause looked for in the electrolyte or in the forming bath. Now I have come across plates measuring 13 in. by 14 in. which have grown in one formation as much as IQ in. high and nearly I in. long, the duration of such formation being a little under forty hours at a current density of 0-003 amperes per sq.cm. of developed surface. This was not an isolated case, but occurred on several occasions in a batch of about 500 plates. Some of these plates, instead of being melted down, were put up for experimental testing, and in three such cells, each containing seven plates, discharged at a high rate (I+ hour), the positives grew vertically 3& in. in five weeks without breaking, bursting, or even buckling, whilst in three other cells discharged at a low rate (Le,, nine hours), the growth was only 13 in. vertically in the same time, and the plates buckled and broke. The formation of a very troublesome and obstinate sulphate of lead often gives serious trouble to the manufacturer.This particular sulphate is not capable of either oxidation or reduction; that is to say, when making Plant6 plates, if this sulphate once develops during the first oxidising process it resists all attempts to decompose it in subsequent reversals. I have devoted much study to this particular sulphate, as I attribute to it those peculiarities experienced in plates that show evidence of not working with uniform current density, and consequently buckle early. As is well known it is not easy to collect sufficient material to work upon from an actual plate, but I have successfully collected some of this particular sulphate, crystal by crystal, when intermixed with PbO, active material, andSTORAGE BATTERIES AND THEIR ELECTROLYTES 229 I have analysed these samples and found them to agree with analyses made by an independent chemist.The compound may be termed a hemibasic sulphate 2PbSO; PbO, whose molecular weight is 829, and which contains 74'9 per cent. of lead, 80.7 per cent. of lead oxide, and 19'3 per cent. of SOs. The troubles experienced with this sulphate alone supply sufficient matter for a separate Paper which may, perhaps, appear in the future. So far we have dealt with the presence of nitrogen compounds alone, but great as are the dangers associated with these alone, they are multiplied ten- fold when some metallic impurity is present also. The most common of such impurities may be said to be iron, and as stated in my Paper of last July (p. 17), it accelerates the deleterious action of nitrogen compounds to an alarming degree.Unfortunately iron appears in small quantities in very nearly all natural waters, in almost all samples of sulphuric acid, in all samples of lead oxides, used for pastes, in a large majority of samples of rain water, and in most so-called distilled waters, taken from the steam boiler in use on the generat- ing plant. I t is, indeed, almost as common an impurity as nitrogen in its various forms, and hence the same care must be taken to keep down the quantity present to the lowest point possible. Although there are many impurities other than iron and nitrogen having deleterious effects on storage batteries, it is principally my intention to deal in this Paper with only these two most common impurities. We will proceed to consider their effect on current density of formation, a matter that has not nearly sufficiently been experimented upon by makers.Different electrolytic reaction take place side by side on the prepared surfaces of the electrodes, and in proportion to the current density adopted, the process may be either an oxidising or a reducing one. Oxidation is most facilitated by concentrated solutions and low current density at the positive, whilst reduction is facilitated by concentrated solutions and low current density at the negative. High current density and dilute solutions do not assist either oxidation or reduction at the respective electrodes, for it is possible that the substance which is reduced at the negative may be oxidised at the positive, and the substance which is oxidised at the positive may be reduced at the negative, and when this happens, the two active opposing currents neutralise each other with the result that no work is done internally.Now, I find by practice and repeated experiments that both ammonia and iron have several oxidising values, and by experimenting with pure sulphuric acid of sp. gr. 1.200, and varying percentages of iron sulphate, that the electrolytic reactions are seriously affected thereby. In one experiment made, 4 voltameters were arranged in series using strips of pure platinum as electrodes, and the electrolyte containing 0'001, 0.01, 0.1, and 1.0 per cent. of iron and ammonia respectively. Test No. I. The platinum electrodes used measured 10 cm. by I cni. Therefore the current rate in amperes multiplied by 10 will give the current density per square decimeter of working surface exposed on one plate.The sulphuric acid used was redistilled and all traces of ammonia removed thereby, and it was found to be quite free from iron when analysed previous to use. This precaution was necessary to ensure the introduction of any substances other than the iron and ammonia salts required.230 STORAGE BATTERIES AND THEIR ELECTROLYTES Current in Amperes. Per Cent. Losses in Gases. Per Cent. Losses in Gases. Per Cent. Losses in Gases. Current in Amperes. Per Cent. Losses of Per Cent. Losses of Per Cent. Losses of Per Cent. Losses of Gases. Gases. Gas. I Gases. 0'1 Per Cent. Fe. I O O I Per Cent. Fe. I 1.0 Per Cent. Fe. O*OOI Per Cent. Fe. Per Cent. Losses in Gases. I 8.9 12.13 17.8 20.6 28.0 10'2 1-07 1'7 1'9 4'2 9'9 1'1 0'22 0.3 I 0.78 0-92 1-13 3-30 0.252 0.156 0109 0053 0'2 I 0'01 I 32'3 50'7 57'3 63'9 75'8 87.8 This experiment was repeated several times with approximately the same results, after which the solution was replaced by pure sulphuric acid of the same density, and ammonia added in the proportions o*oor, 0'01, 0.1, 1.0 per cent., other conditions remaining unchanged.Test No. 2. I 1.0 Per Cent. NH3, I 0.1 Per Cent. NH3. I 0.01 Per Cent. NH3 10001 Per Cent. NH3 0.8 1 '3 1'9 2.6 3'9 5'1 0'253 0.167 0.048 0.009 0'20 I 0'111 11'1 19'4 23'7 29.2 40% 49 '9 3'3 6.1 14'3 19'7 23.8 29.0 0'0 I 0'9 1'7 3'2 4'7 6.8 From these tables we gather the results effected by each impurity separately. The next thing to be done was to combine the two impurities, using the same proportions of each in the one solution.Test No. 3. 1-0 Per Cent. Fe. 1'0 Per Cent. KH3. 0.1 Per Cent. Fe. 01 Per Cent. NH3. 0.01 Per Cent. Fe. O O I Per Cent. NH3. 0001 Per Cent. Fe. yo01 Per Cent. NH3. Current in Ainperes. Per Cent. Losses in Gases. Per Cent. Losses in Gases. Per Cent. Losses in Gases. Per Cent. Losses in Gases. 0.256 0.219 0.161 0.05 I 0.014 0'100 10.6 15'3 2 1.5 29.1 40.2 55'7 43'7 54'2 63.8 84'9 96'7 105.2 2'9 4'7 19'4 26'3 32'4 12'1 1-15 3'8 9'2 17.1 27'3 30'4 These figures as shown in the three separate experiments speak for them- selves. Attention should be called to the fact that nearly all the current densities employed in the experiments are considerably higher than those adopted in the forming of plates, or in the discharge and charge ratesSTORAGE BATTERIES AND THEIR ELECTROLYTES 231 adopted by users ; therefore seeing that the danger increases with decrease of current density, the results to be expected will be all the more serious in practice.It is evident that the effects of these impurities is not a matter to be neglected by manufacturers, and since it is known that all the nitrates and all the nitrogen oxides can, under certain conditions, be reduced to ammonia ; and on the other hand, that ammonia, under certain conditions, can be oxidised through its various stages to nitric acid, it behoves the manu- facturer to watch his cells both in and out of the works wherever these conditions may be found to exist. So far I have referred to my own experiments, but in order to support my observations I am able to bring forward data collected, from different standpoints, however, by other workers.In vol. 111. p. 542, of the Electuo- Chemist and Metallurgist are tabulated the results of a long series of researches by Dr. Franz Peters on the electrolytic formation of PbO,, and I append here a curve, showing how few of the processes there mentioned give anything like efficient results in cases where ammonia or nitrogen has been used. K. Elbs in Zeifs. fiir Elektrochemie, vii. p. 261, gives some confirmatory evidence in relation to the effects of iron in sulphuric acid. J. M. Bell in Journ. Phys. Chem., Dec., 1903, pp. 652-5, gives some further results dealing with the effects of the presence of iron in sulphuric solutions, and confirming the conclusions here set forth.It is evident from a study of these data that the adoption of an economical current density is a most important matter for the manufacturer to study, and a great saving may be effected in cost of production by ascertaining what actual current density is most suitable to every particular type of plate and formation. The current density, however, must not be cut too fine, or possibly erratic behaviour inside the works will be transferred to outside the works. There are to-day several accumulator works using current densities of formation that far exceed those actually and theoretically necessary. In view of the very different behaviours and nature of products when concentration of electrolyte and current density are varied, I would suggest the following simple experiment : Take pure metallic lead plates, and immerse in baths containing sulphuric acid of, say, 1.100 sp.gr., and varying percentages of nitric acid or some nitrogen salt.If a series of such experimental cells be subjected to a fixed current density for a fixed number of hours, and the positive plates carefully watched, very different behaviour will be noticed in the different cells, some cases producing a copious supply of peroxide of lead, such peroxide precipitated as fast as it is formed ; others producing no precipitate but very nearly the same quantity of peroxide of lead, strongly adherent ; other cases producing peroxide, very much inter- mixed with a sulphate of lead ; and, finally, if the percentage of nitric acid be high (say about 2 per cent.), nothing being produced but white sulphate of lead with scarcely a trace of peroxide intermixed, This experiment should be also carried out by using a series of cells of the same concentration throughout, but a different current density for each, when the results obtained will be practically the same.It is evident that there is in every case a current density most suitable for every existing con- dition. The diagram (Fig. I) shows how the percentage of PbO, varies in proportion to the mixture per 100 ampere-hours applied. The dotted line indicates the ampere-hours applied, the thick black line indicates the number of grams produced, the thin line indicates the percentage of PbO, to that of the energy required to produce it.It will be noticed that in some cases the production of peroxide of lead is high compared232 STORAGE BATTERIES AND THEIR ELECTROLYTES ii 'kSTORAGE BATTERIES AND THEIR ELECTROLYTES 233 to cost of energy, whilst in others the reverse is the case ; therefore there are profitable processes and unprofitable ones, and if a maker has already a profitable one it is undoubtedly to his advantage to make it as much more profitable as he possibly can. In the early days of the Epstein type of plate, which I believe is still being manufactured with success, ammonia and ammonium salts in combina- tion with potassium, sodium, aluminium, and calcium salts were used very plentifully in the process of manufacture. But in 1891 it was accidentally discovered that better plates were obtained by avoiding the use of such salts in the forming bath, and no doubt many similar cases experienced could be quoted. I have indeed made the ammonia question a special study, princi- pally because I have had much to do with ammonium processes, and there- fore have been fortunate in being able to gather much information on the subject during the past fifteen years, and I must admit that to avoid the entry of ammonia and iron into the works or the battery-room is a most difficult, if not impossible, matter ; but there is sufficient evidence to show that a great deal of trouble can be avoided, and a great deal of saving effected, if an effort is madc by makers to avoid these impurities as much as possible, by extra care in their own works, and by stringent rules and instruc- tions to users of their plates outside the works. To insist upon its total elimina- tion would make the future of the storage battery such that, instead of being an essential section of an electrical generating plant, it will become a luxury. But when, as I shall show later, one can find actual proofs of batteries having been started with electrolytes containing only small percentages of ammonia and iron, and subsequently doubling and even trebling the quanti- ties present in less than the first year's working, then it is time that manu- facturers should do their utmost to bring the responsibility of failure upon the shoulders of the right person, and to do this they must first adopt such methods in their own works that there will be no possibility of failures being ascribed to failure on their part to eliminate all dangerous impurities.

ISSN:0014-7672    

DOI:10.1039/TF9070200222

出版商:RSC    

年代:1907

数据来源: RSC

摘要:

STORAGE BATTERIES AND THEIR ELECTROLYTES 233 DISCUSSION. Mr. H. L. Joly said that he was afraid he must have had a wrong notion as to what a Paper should be ; he thought that such a communication should be a crystallised embodiment of careful experiment and theory, but the present Paper appeared to him a colloidal mass of hints, generalities, and unfinished research, while a fresh perusal of the Paper of which this one was a sequel hardly helped one to reach a satisfactory conclusion. Taking the Paper page by page, he found that the author bewailed the ignorance and care- lessness of battery makers, and quoted figures intended to show the uniformity apparently prevailing in the accumulator trade. He thought that for many years nearly every accumulator factory boasted of a Reichsanstalt of its own, and that the uniformity was apparent only in the failures of the ‘i inventions ” issued from the laboratories to reach a healthy commercial stage.Price varied for certain cells of a given capacity, in a standard container and given weight, between 64d. and IS. 3d. per plate. The reference to careless workmen showed forcibly the need to educate the men, and if they were refractory to intellectual training, to keep over them a foreman with keen eyes. Over-forming has often caused greater trouble than under-formation.234 STORAGE BATTERIES AND THEIR ELECTROLYTES The advice to remove to the country, for pure air and siniple life, was a counsel of perfection ; works could not be erected near heaven and benefit by cheap rates of transport, besides which everybody was now removing to the country to escape rates rather than impurities in the atmosphere.The author sees in ammonia the greatest incubus that ever beset accumu- lator manufacture, and yet, as he says, the question has not yet been thoroughly investigated ; why, therefore, not refrain from considering the case against ammonia as proven before placing a record indisputable scientific evidence thereof ? Nitrogen forms a large part of our atmosphere, and it happens to be useful in many respects. Its compounds are easily detected, and with care their introduction in cells can be prevented. The author quotes on page 227 some erratic results which he attributes to nitrogen compounds, but he expects us to receive this statement without giving us any detail as to the cells, their history, &c., and we cannot discuss his opinion any more than accept it implicitly if he means that such trouble was due to spontaneous absorption of atmospheric impurities by the electrolyte.Coming now to the vital question of sulphate, he had examined micro- scopically many plates for the presence of sulphate (or sulphates), and he thought it a difficult matter to collect enough from one plate for satisfactory analysis ; collecting from various plates would introduce varying conditions, and if the author’s theory were correct, could hardly be accepted. He would much like to see the actual crystals of this so-callcd hemibasic salt, and to hear more, not about the trouble it causes, but about its physical charactcr- istics, density, crystallography, solubility, &c.He thought that this salt might be a mixture of ordinary PbSO, and Kuhn’s sulphate PbSO,PbO, which was originally obtained by digesting PbSO, with ammonia. He wondered whether through some lapse of memory the author had not inadvertently mixed up his experimental sulphates. Regarding the voltameter tests, the gas analysis study of the oxygen efficiency of the accumulator had already been done by Dr. Rokotnitz with lead electrodes, not platinum, and as nobody would dream of using platinum as an auxiliary electrode in accumulator research, he thought figures obtained by Rokotnitz, method would be more valuable than those given by the author. The tendency was now to abandon the delicate mercury electrode, and even cadmium, to use the spongy lead test plate, much more consistent in the results it gave, and capable of immediate interpretation by ordinary battery workers without scientific training. It was therefore a pity that the author, as a man of practical achievements, should have used platinum, and moreover given such scant information about his voltametric measurements.Had he used lead plates, the analysis of the gases evolved would have proved of some interest and perhaps helped to further the author’s theory. In summing up, the author touched upon the vital point of the whole question; perfect purity would be a luxury. We could hardly picture a trust of accumulator makers selling certified pure acid and water, and keeping a watch on the atmosphere of their clients’ battery rooms, to facilitate their fulfilment of maintenance contracts.The author proposed to show later further proof of the noxious effects of nitrogen compounds, It was to be hoped that he would find it possible to gather them all into one terse, lucid, and decisive Paper, and when such a Paper came, if the author could prove his case satisfactorily, he would be the first to congratulate him thereupon. Dr. A. C. Cumming said that for a prolonged experiment it was better to avoid the use of platinum electrodes, since a minute trace of platinum inSTORAGE BATTERIES AND THEIR ELECTROLYTES 235 the solution was sufficient to ruin the cell by causing evolution of gas. If possible the lead peroxide should be deposited on a lead plate, but if it was necessary to use platinum it should be coated with platinum black and a fresh coat of lead peroxide given for each experiment.Regarding the ammonia question, was it not a fact that some one had recommended washing with ammonium acetate solution to renovate them ? Of course, in view of the bad effect of ammonium salts, it would really have the opposite effect. Mr. W. R. Cooper was sorry that the discussion had not been taken up more readily by manufacturers. He supported the opinions of Mr. Joly on the Paper, which seemed as if it had been written too hurriedly. The table on page 223 was compiled from 1902 tests. The author should have utilised more recent material than that four years old, and the reference to a curve on page 231 is not very clear. In the experimental results given on page 230, which are stated “ to speak for themselves,” no reference to the duration of the experiments is made, and they seemed to him to be vague.Mr. R. W. Vicarey (communicaled reply) : In reply to Mr. Joly, I regret that he should think that I was under a wrong impression as to what should constitute a Paper. I agree with him that it should be a crystallised embodi- ment of careful experiment and theory, but would point out that experiments in accumulator work necessarily extend to very long periods and involve great expense, and even when such experiments are crystallised to their smallest embodiment they are likely to form a Paper containing too large a quantity of matter for any society to publish. During my experience of nearly twenty years I have been able to collect a very valuable series of experimental information which throws much light upon the question of ammonia in storage batteries, but it is impossible to quote in a Paper these experiments in detail to be sufficiently conclusive to satisfy scientific inquiries.My principal object is to excite interest in others, being now satisfied myself upon the point. As regards the troubles experienced. by careless workmen, all manufac- turers will be able fully to understand me, although they may not desire to comment upon the matter. As regards removal to pure air, I am pleased to note that my advice is thought a counsel of perfection, and I think that Mr. Joly will have to admit that although we are none of us perfect, we must all aim to become so as far as we possibly can, and none can deny that town air contains far more ammonia than country air.I am quite prepared to have the subject of my Papers doubted to a very large extent, and I myself, on page z of my first Paper, specially point out that although my investigations start from 1893, “ it was not until 1902 that I received final confirmation to convince me absolutely,” and therefore I cannot be surprised at others not accepting my statements at once. I would strongly suggest to Mr. Joly what I have suggested to others with great success, namely, not to take what I say as facts, but try some experiments for himself, extending them over a period of more than one year, and less than two, and then bringing his results in a Paper before this Society, when, if I am wrong, I shall honestly admit the fact.I t is the necessity for extended duration of most carefully watched circumstances and data that makes reliable information so difficult to obtain, but if expense is not a matter of consideration, there is a very simple and easy method as given in my first Paper on page 2, i.e., “ Break a Winchester of ammonia in a battery room and watch the results.” If I am wrong it will cost nothing ; if I am right it will cost a very great deal. Will any one try this 1 VOL. 11-T9236 STORAGE BATTERIES AND THEIR ELECTROLYTES My remarks on the erratic behaviour of the plates in the present Paper do not refer to atmospheric nitrogen impurities, but to the nitrogen used in the manufacturing process. With reference to the sulphates, my remarks specially apply to the manufacturers’ experience in the works, and seeing that this sulphate often occurs in fairly large patches on the plates during their formation, it is more easy to collect this sulphate in large quantities for analysis than Mr.Joly appears to imagine. I willendeavour to obtain some for him, so that he may investigate its special properties for himself. With reference to my using platinum plates, a point also raised by Dr. Cumming, I had reasons for doing this which I need not explain, but I would point out that the differences of results, whether platinum or fully-formed lead plates are used, is negligible for all practical purposes, unless the experiments are of long duration, in which case lead is to be preferred. Replying to Dr.Cumming on the ammonia question, it is quite correct that ammonium acetate has been used for the desulphating of badly sulphated plates, and ammonium sulphate is used by some makers at the present day for washing and for forming the plates, but if data has been kept of such plates as may not have been properly washed, or not had the ammonia entirely eliminated, it will be found that the use of ammonia is not so beneficial as it is supposed to be. In reply to Mr. Cooper, it is a pity that the subject is not taken up with more interest by the manufacturers, as it certainly is of great importance to them and I had hoped to have heard some confirmations of my remarks. It is a very difficult matter to write a quite satisfactory Paper on a subject that covers so large a field,and Papers when too long are very apt to become most uninteresting to their readers.Reference to the curve will be readily understood if it is compared with the table found in vol. iii., page.542, of the Electro-Chemist arid Metalluigist, as the references giving the solutions used will be found on the abscissae. As regards the duration of the voltameter experiments, these were con- ducted as representing the gas losses that would occur during the three-, six-, nine-, and twelve-hour charge of a battery, and the duration of the tests were these periods respectively. STORAGE BATTERIES AND THEIR ELECTROLYTES 233 DISCUSSION. Mr. H. L. Joly said that he was afraid he must have had a wrong notion as to what a Paper should be ; he thought that such a communication should be a crystallised embodiment of careful experiment and theory, but the present Paper appeared to him a colloidal mass of hints, generalities, and unfinished research, while a fresh perusal of the Paper of which this one was a sequel hardly helped one to reach a satisfactory conclusion.Taking the Paper page by page, he found that the author bewailed the ignorance and care- lessness of battery makers, and quoted figures intended to show the uniformity apparently prevailing in the accumulator trade. He thought that for many years nearly every accumulator factory boasted of a Reichsanstalt of its own, and that the uniformity was apparent only in the failures of the ‘i inventions ” issued from the laboratories to reach a healthy commercial stage.Price varied for certain cells of a given capacity, in a standard container and given weight, between 64d. and IS. 3d. per plate. The reference to careless workmen showed forcibly the need to educate the men, and if they were refractory to intellectual training, to keep over them a foreman with keen eyes. Over-forming has often caused greater trouble than under-formation.234 STORAGE BATTERIES AND THEIR ELECTROLYTES The advice to remove to the country, for pure air and siniple life, was a counsel of perfection ; works could not be erected near heaven and benefit by cheap rates of transport, besides which everybody was now removing to the country to escape rates rather than impurities in the atmosphere. The author sees in ammonia the greatest incubus that ever beset accumu- lator manufacture, and yet, as he says, the question has not yet been thoroughly investigated ; why, therefore, not refrain from considering the case against ammonia as proven before placing a record indisputable scientific evidence thereof ? Nitrogen forms a large part of our atmosphere, and it happens to be useful in many respects.Its compounds are easily detected, and with care their introduction in cells can be prevented. The author quotes on page 227 some erratic results which he attributes to nitrogen compounds, but he expects us to receive this statement without giving us any detail as to the cells, their history, &c., and we cannot discuss his opinion any more than accept it implicitly if he means that such trouble was due to spontaneous absorption of atmospheric impurities by the electrolyte.Coming now to the vital question of sulphate, he had examined micro- scopically many plates for the presence of sulphate (or sulphates), and he thought it a difficult matter to collect enough from one plate for satisfactory analysis ; collecting from various plates would introduce varying conditions, and if the author’s theory were correct, could hardly be accepted. He would much like to see the actual crystals of this so-callcd hemibasic salt, and to hear more, not about the trouble it causes, but about its physical charactcr- istics, density, crystallography, solubility, &c. He thought that this salt might be a mixture of ordinary PbSO, and Kuhn’s sulphate PbSO,PbO, which was originally obtained by digesting PbSO, with ammonia.He wondered whether through some lapse of memory the author had not inadvertently mixed up his experimental sulphates. Regarding the voltameter tests, the gas analysis study of the oxygen efficiency of the accumulator had already been done by Dr. Rokotnitz with lead electrodes, not platinum, and as nobody would dream of using platinum as an auxiliary electrode in accumulator research, he thought figures obtained by Rokotnitz, method would be more valuable than those given by the author. The tendency was now to abandon the delicate mercury electrode, and even cadmium, to use the spongy lead test plate, much more consistent in the results it gave, and capable of immediate interpretation by ordinary battery workers without scientific training.It was therefore a pity that the author, as a man of practical achievements, should have used platinum, and moreover given such scant information about his voltametric measurements. Had he used lead plates, the analysis of the gases evolved would have proved of some interest and perhaps helped to further the author’s theory. In summing up, the author touched upon the vital point of the whole question; perfect purity would be a luxury. We could hardly picture a trust of accumulator makers selling certified pure acid and water, and keeping a watch on the atmosphere of their clients’ battery rooms, to facilitate their fulfilment of maintenance contracts. The author proposed to show later further proof of the noxious effects of nitrogen compounds, It was to be hoped that he would find it possible to gather them all into one terse, lucid, and decisive Paper, and when such a Paper came, if the author could prove his case satisfactorily, he would be the first to congratulate him thereupon.Dr. A. C. Cumming said that for a prolonged experiment it was better to avoid the use of platinum electrodes, since a minute trace of platinum inSTORAGE BATTERIES AND THEIR ELECTROLYTES 235 the solution was sufficient to ruin the cell by causing evolution of gas. If possible the lead peroxide should be deposited on a lead plate, but if it was necessary to use platinum it should be coated with platinum black and a fresh coat of lead peroxide given for each experiment. Regarding the ammonia question, was it not a fact that some one had recommended washing with ammonium acetate solution to renovate them ? Of course, in view of the bad effect of ammonium salts, it would really have the opposite effect.Mr. W. R. Cooper was sorry that the discussion had not been taken up more readily by manufacturers. He supported the opinions of Mr. Joly on the Paper, which seemed as if it had been written too hurriedly. The table on page 223 was compiled from 1902 tests. The author should have utilised more recent material than that four years old, and the reference to a curve on page 231 is not very clear. In the experimental results given on page 230, which are stated “ to speak for themselves,” no reference to the duration of the experiments is made, and they seemed to him to be vague. Mr. R.W. Vicarey (communicaled reply) : In reply to Mr. Joly, I regret that he should think that I was under a wrong impression as to what should constitute a Paper. I agree with him that it should be a crystallised embodi- ment of careful experiment and theory, but would point out that experiments in accumulator work necessarily extend to very long periods and involve great expense, and even when such experiments are crystallised to their smallest embodiment they are likely to form a Paper containing too large a quantity of matter for any society to publish. During my experience of nearly twenty years I have been able to collect a very valuable series of experimental information which throws much light upon the question of ammonia in storage batteries, but it is impossible to quote in a Paper these experiments in detail to be sufficiently conclusive to satisfy scientific inquiries.My principal object is to excite interest in others, being now satisfied myself upon the point. As regards the troubles experienced. by careless workmen, all manufac- turers will be able fully to understand me, although they may not desire to comment upon the matter. As regards removal to pure air, I am pleased to note that my advice is thought a counsel of perfection, and I think that Mr. Joly will have to admit that although we are none of us perfect, we must all aim to become so as far as we possibly can, and none can deny that town air contains far more ammonia than country air. I am quite prepared to have the subject of my Papers doubted to a very large extent, and I myself, on page z of my first Paper, specially point out that although my investigations start from 1893, “ it was not until 1902 that I received final confirmation to convince me absolutely,” and therefore I cannot be surprised at others not accepting my statements at once.I would strongly suggest to Mr. Joly what I have suggested to others with great success, namely, not to take what I say as facts, but try some experiments for himself, extending them over a period of more than one year, and less than two, and then bringing his results in a Paper before this Society, when, if I am wrong, I shall honestly admit the fact. I t is the necessity for extended duration of most carefully watched circumstances and data that makes reliable information so difficult to obtain, but if expense is not a matter of consideration, there is a very simple and easy method as given in my first Paper on page 2, i.e., “ Break a Winchester of ammonia in a battery room and watch the results.” If I am wrong it will cost nothing ; if I am right it will cost a very great deal.Will any one try this 1 VOL. 11-T9236 STORAGE BATTERIES AND THEIR ELECTROLYTES My remarks on the erratic behaviour of the plates in the present Paper do not refer to atmospheric nitrogen impurities, but to the nitrogen used in the manufacturing process. With reference to the sulphates, my remarks specially apply to the manufacturers’ experience in the works, and seeing that this sulphate often occurs in fairly large patches on the plates during their formation, it is more easy to collect this sulphate in large quantities for analysis than Mr. Joly appears to imagine.I willendeavour to obtain some for him, so that he may investigate its special properties for himself. With reference to my using platinum plates, a point also raised by Dr. Cumming, I had reasons for doing this which I need not explain, but I would point out that the differences of results, whether platinum or fully-formed lead plates are used, is negligible for all practical purposes, unless the experiments are of long duration, in which case lead is to be preferred. Replying to Dr. Cumming on the ammonia question, it is quite correct that ammonium acetate has been used for the desulphating of badly sulphated plates, and ammonium sulphate is used by some makers at the present day for washing and for forming the plates, but if data has been kept of such plates as may not have been properly washed, or not had the ammonia entirely eliminated, it will be found that the use of ammonia is not so beneficial as it is supposed to be. In reply to Mr. Cooper, it is a pity that the subject is not taken up with more interest by the manufacturers, as it certainly is of great importance to them and I had hoped to have heard some confirmations of my remarks. It is a very difficult matter to write a quite satisfactory Paper on a subject that covers so large a field,and Papers when too long are very apt to become most uninteresting to their readers. Reference to the curve will be readily understood if it is compared with the table found in vol. iii., page.542, of the Electro-Chemist arid Metalluigist, as the references giving the solutions used will be found on the abscissae. As regards the duration of the voltameter experiments, these were con- ducted as representing the gas losses that would occur during the three-, six-, nine-, and twelve-hour charge of a battery, and the duration of the tests were these periods respectively.

ISSN:0014-7672    

DOI:10.1039/TF9070200233

出版商:RSC    

年代:1907

数据来源: RSC