May 6, 1909] 



NA TURE 



297 



water, gluten gradually loses its coherence, and disperses 

 as a cloudy, colloidal solution or hydrosol, which is pre- 

 cipitated by a trace of salt or alkali. The change is due, 

 not to the water, but to the carbonic acid which is pre- 

 sent. In the absence of salts cohesion is destroyed by 

 traces of acid or alkali. With low salt content ooooi 

 normal acid, for instance, disperses the protein almost 

 instantaneously. Strong acids, however,' disperse gluten 

 only when their concentration is low. Above a certain 

 critical value, e.g. 0.05 normal HCl, the acid restores and 

 maintains cohesion. Alkalies act in the same way. 



A hydrosol of gluten is precipitated by salt, and the 

 gluten restored to its characteristic stringy state. There 

 is, therefore, an antagonism between salts and acids or 

 alkalies. 



The relations between acids and salts were investigated 

 by varying the concentration of acid and determining the 

 concentration of salt necessary to maintain cohesion, i.e. 

 to oppose completely the dispersive power of the acid. 

 The results show that at first, as the concentration of 

 acid increases, the concentration of salt must be increased 

 also until a point is reached beyond which further addition 

 of acid lessens the quantity of salt which is needed to 

 preserve cohesion. 



We may conclude from this that the dispersive action 

 of acid increases with increasing concentration to a maxi- 

 mum beyond which it decreases to zero. A weak acid, 

 such as lactic acid, will not maintain cohesion at any 

 concentration. 



Very dilute acid or alkali breaks up coherent gluten by 

 forming round each protein particle a double electric layer. 

 The protein may be looked upon as an amphoteric electro- 

 lyte similar to an amino-acid. It reacts with acids or 

 alkalies to form salts of a peculiar nature, which, by 

 ionisation, form double electric layers. Excess acid or 

 alkali suppresses the feeble ionisation, and so restores 

 cohesion. 



The potential difference between protein and fluid was 

 determined by measurements of the migration of the protein 

 in unit field. It was found to increase with increase in 

 the concentration of a strong acid up to a maximum, 

 beyond which it diminishes. The curve expressing the 

 relation of concentration of acid to the potential differ- 

 ence has the same form as that which expresses the effect 

 of a salt upon the dispersive power of acid. Salts act 

 by preventing the formation of electric double layers. 



April 29. — Sir Archibald Geikie, K.C.B., president, .in 

 the chair. — Xote on the results of cooling certain hydrated 

 platin-cyanidcs in liquid air : J. Emerson Reynolds. 

 Some months ago Sir James Dewar directed the writer's 

 attention to the fact that a colourless crystalline material, 

 which was supposed to be lithium platino-cyanide, became 

 temporarily red when cooled in liquid air. On repeating 

 the experiment with some of the material which Sir James 

 Dewar had placed in the writer's hands for examina- 

 tion, he found that, after several repetitions of the treat- 

 ment, a permanent yellow substance was also formed, 

 which did not return to the usual colourless condition at 

 ordinary temperatures. Chemical examination of the 

 material led to the conclusion that it was a mixture of 

 lithium chloride, cyanide, and sulphate, including merely 

 a trace of platino-cyanide, but that rather less than 5 per 

 cent, of lilhium platinicyniiide was present, and that the 

 colour changes at low temperatures were due to the 

 presence of the latter salt. Pure lithium platino-cyanide 

 was freshly prepared for comparison, and when analysed 

 was found to consist of Li,Pt(CN),|,5H,0. The grass- 

 green crystals of this salt did not become red when 

 immersed in liquid air, but merely became paler in tint, 

 therefore that salt could not be concerned in the produc- 

 tion of the phenomena noted above. On the other hand, 

 pure lithium platinicyanide, when fully hydrated, was 

 shown by analysis to have the composition 



Li,Pt(CN)3,3H,0. 



When the nearly colourless crystals of this compound were 

 slowly cooled in liquid air they became of an intense red 

 colour, and this change was found to coincide with the 

 loss of one molecule of water of crystallisation, which was 

 resumed when the temperature was allowed to rise, the 

 NO. 2062, VOL. 80] 



colourless tri-hydrate being reproduced. Further, on rapid 

 cooling of the tri-hydrate, a portion always passed beyond 

 the red stage, and more or less of a yellow substance was 

 formed. This turned out to be a yellow mono-hydrate. 

 This hydrate also resumes water at ordinary temperatures, 

 and affords the colourless tri-hydrate ; but it was found 

 that when certain neutral salts are present, as in the case 

 of Sir J. Dewar's material, this re-hydration is inhibited, 

 and the yellow mono-hydrate persists at higher tempera- 

 ture — hence all the phenomena noted at the outset were 

 explained. Similar changes of colour and composition can 

 be effected by heating the platinicyanide, but this appears 

 to be the first case in which successive stages of dehydra- 

 tion of a crystallised salt have been traced on cooling the 

 substance in liquid air. — A phenomenon connected with the 

 discharge of electricity from pointed conductors ; with a 

 note by John Zeleny : H. T. Barnes and A. N. Shaw. 

 In the study of point discharge made by Prof. John 

 Zeleny, it was noticed that, when examined under the 

 microscope, steel needle points, after discharging as anode, 

 showed an irregular deposit, which extended outwards 

 some little distance, and resembled ordinary rust. A 

 much smaller deposit was noticed when the point was 

 made the kathode. The authors have investigated, some- 

 what in detail, the character of this deposit, not only for 

 steel points, but also for points of other metals. Using a 

 microscope of high power, it was possible to distinguish 

 characteristic forms of the deposit. These the authors 

 classify as (i) a granular deposit; (2) a tubular deposit; 

 (3) a smooth formation ; and (4) a thin film formation. 

 The four types are all probably connected with each other, 

 but in appearance they are quite distinct. The tubular 

 formation is perhaps the most interesting, and appears to 

 be a tube of oxide growing up around a minute droplet 

 of water, or, perhaps, hydrogen peroxide. These tubes 

 were seen to elongate under the microscope when blown 

 upon by moist air, and to swell up at the end as though 

 water vapour were condensing through the thin film of 

 oxide closing the tube. In some cases the swelling caused 

 the oxide film to burst. In dry air the liquid appeared to 

 recede in the tube, leaving a hard, horny structure of oxide 

 extended. The granular deposit appeared to be broken 

 down tubes, while the smooth formation appeared to be 

 drops of liquid with oxide so hardened as to be incapable 

 of extension. The thin film formation was produced only 

 on metals less easily oxidised. The appearance of water 

 drops on the point makes it seem probable that it is the 

 water vapour in the discharge chamber which has con- 

 densed around the negative ions and been swept into the 

 anode point. Discharging i-n absolutely dry air gave no 

 sign of any deposit on even the most easily oxidised metals. 

 The slightest trace of moisture in the chamber caused a 

 growth of deposit as much as 50 per cent, of the total 

 amount obtained when discharging in steam. The metals 

 giving the greatest deposit were aluminium, zinc, steel, 

 and cadmium, while gold was found to give no deposit 

 at all. Prof. Zeleny points out that the presence of water 

 droplets on the point indicates a much lower temperature 

 there than the luminosity might lead us to expect. This 

 he verifies by making a .point out of the junction of two 

 dissimilar metals. — The efifect of temperature on ionisation : 

 J. A. Crowther. The effect of temperature on the ionisa- 

 tion produced in a gas by Rontgen rays was first investi- 

 gated by Perrin, who, using air, concluded that the total 

 ionisation in a gas was independent of the temperature if 

 the pressure were kept constant. McClung, however, who 

 repeated these experiments later with air, carbon dioxide, 

 and hydrogen, found that the ionisation in a gas was 

 independent of the temperature if the density of the gas 

 is kept constant, that is, if it is heated at constant volume. 

 Although no source of error could be indicated in Perrin 's 

 work, there was little doubt that the later experiments of 

 McClung were correct, and that between the limits of his 

 experiments (15° C. to 272° C.) and for the gases used 

 the ionisation "produced by Rontgen rays was independent 

 of the temperature when the gas was kept at constant 

 density. It is well known that the ionisation produced by 

 rays of given intensity in certain gases and vapours, for 

 example, methyl iodide, ethyl bromide, or carbon tetra- 

 chloride, is much greater than that in air or carbon 

 dioxide. The present investigation was made to discover 



