July i8, 1895] 



NA TURE 



287 



during electrolysis are observed by tracing the formation of the 

 precipitates which they give with a trace of a suitable indicator. 

 Thus solid agar jelly solutions of barium chloride and of sodium 

 chloride containing a little sodium sulphate were set u|) in contact, 

 and a current passed across the junction. The barium ions form 

 a little insoluble barium sulphate as they travel, and so their 

 velocity can be measured. The specific ionic velocity under a 

 potential gradient of one volt per centimetre can then be calcu- 

 lated, the area of cross section of the lube, in which the solutions 

 are placed, the mean specific resistance of the solutions, and the 

 strength of current being known. The follow ing table gives a 

 comparison between the results thus obtained and the numbers 

 theoretically deduced by Kohlrausch from the migration con- 

 stants and the conductivities of the corresponding aqueous 

 solutions : — 



Calculated velocity in 

 cm. per sec. 



Barium ... 0'00037 



Calcium ... o'ooo29 



Silver ... ... 0'00046 



Sulphate group (SO4) 000049 



Ob.served velocity in 

 cm. per sec. 



o '00039 

 0"ooo35 

 0-00049 

 o '00045 



June 20. — " On the Occlusion of O.xygen and Hydrogen 

 by Platinum Black." Part I. By Dr. Ludwig Mond, F. R.S., 

 Prof W. Ramsay, F. K.S..and Dr. John .Shields. 



The authors describe some preliminary experiments on the 

 occlusion of oxygen and hydrogen by platinum sponge and foil, 

 which in general confirm the results obtained by Graham. At 

 most only a few volumes of these gases are occluded by the more 

 coherent forms of platimmi. 



.■\fter giving details of what they consider the best method of 

 preparation of jilatinum black, they next describe some experi- 

 ments which had for their object the determination of the total 

 quantity of water retained by jilatinum black, dried at 100^ C., 

 and the amount of water which can be removed from platinum 

 black at various temperatures in vacuo. As the result of these 

 experiments they find that platinum black dried at 100^ retains 

 in general 0'5 per cent, of water, and this can only be removed 

 in vacuo al a temperature (about 400*) at which the black no 

 longer exists as such, but is converted at least partially into 

 sponge. At any given temperature the water retained by 

 platinum black seems to be constant. The density of platinum 

 black dried at 100° C. is I9'4, or allowing for the water retained 

 by it at this temperature, 21 '5. 



The amount of oxygen given off by platinum black at various 

 temperatures was determined. .Vltogether it contains about 100 

 volumes of oxygen : the oxygen hegins to come ofi" in quantity at 

 about 300' C. in vacuo, and the bulk of it can be extracted at 

 400' C. , but a red heat is necessary for its complete ren\oval. 

 Small quantities of carbon dioxide were also extracted, chiefly 

 between 100-200° C. 



In determining the quantity of hydrogen occluded by platinum 

 black the authors have carefully distinguished between the 

 hyilrogen which goes to form water with the oxygen always 

 contained in j>lalinum black, and that which is really absorbed 

 by the platinum per sc. Altogether aliout 310 volumes of 

 hydrogen are absorbed per unit volume of platinum black, but 

 of this 200 volumes are converted into water, or only 1 10 volumes 

 are really occluded by the platinum. Part of it can be again 

 removed at the ordinary temperature in vacuo ; by far the larger 

 portion can be extracted at about 250-300" C, but a red heat 

 is necessary for its complete removal. The amount of hydrogen 

 absorbed by platinum is very largely influenced by .slight traces 

 of impurity, probably grease or other matter which fornts a skin 

 over the platinum. 



Platinum black in vacuo absorbs a certain qu.antity of 

 hydrogen. On increasing the pressure of the hydrogen up to 

 about 200-300 mm. a further (juantity is absorbed, but after this 

 pressure is almost without eft'ect. By increasing the pressure 

 from one atTnospherc up to four and a half atmospheres, only 

 one additional volume of hydrogen was absorbed. On placing 

 platinum black charged with oxygen in an atmosphere of 

 oxygen, and increasing the pressure to the same extent, eight 

 and a half additional volumes were however absorbed. 



Platinum lilack charged with hydrogen and ])laced in an 

 atmosphere of hydrogen kept approximately at atmospheric 



NO. 1342, VOL. 52] 



pressure, and platinum black charged with oxygen and confined 

 in an atmosphere of oxygen, behave quite differently when 

 heated. In the former case hydr(jgen is imme<liately expelled 

 on raising the temperature, whilst in the latter case oxygen is 

 steadily absorbed until a temperature of about 360' C. (the 

 temperature of maximum absorption) is reached, when on 

 further heating oxygen begins to come o(T again. 



Incidentally it was noticed that mercury begins to combine 

 with oxygen at 237° C. , and that a mixture of platinum black 

 and phosphorus pentoxide absorbs oxygen al a high temperature, 

 probaljly with the formation of a phosphate or pyrophosphate. 



In the discussion of the results special reference is made to the 

 work of Berliner and Berthelot, and it is pointed out that there 

 is not suflicient evidence for the existence of such chemical 

 compounds as PtjoHj and Ptjnll;. Moreover, the authors are 

 of opinion that the heats of combination of hydrogen and 

 platinum as determined by Berthelot and Favre are valueless, 

 and that the heat which they measured is due for the most part 

 if nut entirely to the formation of water by the oxygen always 

 contained in platinum black. It has yet to be prcned that the 

 absorption of hydrogen by pure platinum black is attended by the 

 evolution of heat, and as regards the formation of supposed true 

 chemical compounds, solid solutions, or alloys, the authors 

 prefer to wait until suflicient data have been accumulated for an 

 adequate inquiry before coming to any definite conclusion. 



Royal Microscopical Society, May 15. — E. .M. Nelson, 

 Vice-President, in the chair. — Messrs. Watson and Sons ex- 

 hibited a simple centring underfitting for use with any ordinary 

 student's microscope. — The Chairman exhibited a new low- 

 lower lens by Zeiss, and a new photographic lens. — .Mr. 

 W. C. Bosanquet read a paper on the anatomy of Nycto- 

 Iheriis ovalis. — Mr. G. C. Karop read a paper, by Dr. A. 

 Bruce, describing a new microtome for cutting sections. — The 

 Chairman announced that the library would be closed from 

 August 12 to .September 9, and that the next. meeting would be 

 on (October 16. 



Mineralogical Society, June 18. — Lewisite and Zirkelite, 



two new Brazilian minerals, by Dr. E. Hussak, of the 

 Geological Survey of Sao Paulo, and Mr. G. T. Prior. 

 Lewisite is a new titano-antimonate of calcium and iron, which 

 was found with xenotime, monazite, cinnabar and other minerals 

 in the heavj' sand obtained by washing the gravel from a hill 

 slope at the cinnabar mine of Tripuhy, Minas Geraes, Brazil. It 

 is cubic, occurs in small brown tran.slucent octahedra, and has 

 the composition 5RO. 3.Sb„05.2Ti02. Zirkelite is a new titano- 

 zirconate of calcium and iron found in association with the new 

 zirconia mineral baddeleyite in the magnetite-pyroxenite 

 from Jacupiranga, Sao Paulo, Brazil. It is cubic, occurs 

 in Ijlack octahedra, and contains about 80 per cent. 

 of ZrO,^ and TiO.,. The authors descrilie the physical and 

 chemical characters of the tw'o minerals, and also give 

 an account of the minerals associated with the Lewisite at 

 Tripuhy ; amongst these occurs sparingly a new titano- 

 antimonate of iron, the description of which will be completed 

 when more material is obtained. 



P.VRIS. 



Academy of Sciences, July 8. — M. Marey in the chair. — 

 On the phy.sical characteristics of the moon and the interpretation 

 of certain surface details revealed by photographs, by .MM. 

 Loewy and P. Puiseux. A general discussion of surface charac- 

 ters of the moon and their origin, and comparison with certain 

 terrestrial features of possibly similar origin. — 0\\ the manner in 

 which any confused but periodic wave-agitation becomes regular 

 in the distance, reducing to a simple wave, by M. J. Bous.sinesq. 

 — Action of zinc chloride on resorcinol, by M. E. Grimaux. — 

 Comparison of the work done by muscles in the case of positive 

 work with that developed in the corresponding case of negative 

 work, by M. k. Chauveau. — Law of the distribution of mean 

 magnetism at (he surface of the globe, by General Alexis de 

 Tillo. — Volumes of salts in their aqueous solutions, by .\I. 

 Lecoci de Boisbaudran. The author considers all soUible 

 substances to belong to a continuous series of which the members 

 at the one end may show dilatation on solution, whereas the 

 members at the other end may exhibit contraction under similar 

 circumstances. He illustrates his theory by examples demon- 

 strating that the former at low temperatures give contraction also 

 on solution, whereas the bodies usually showing contraction on 

 solution exhibit dilatation on .solution in sufficiently concentrated 



