THE COLLOIDAL STATE 105 



salts of glycocoll with calcium chloride and lithium chloride, although none could 

 be obtained with potassium chloride. A fact which also makes the evidence rather 

 uncertain is that, in order to maintain constant composition in successive re- 

 crystallisation, it was necessary to add dilute acetic acid. If recrystallised from 

 water, no constant composition was shown. 



I have repeated some of these experiments, but have been unable to get crystals of 

 constant composition, even using acetic acid, and have been compelled to conclude that the 

 preparations of Pfeiffer and Modelski consisted of mixed crystals, although it is difficult to 

 account for their results being in accordance with these required by the chemical formula?. 

 I found that, unless the solutions were very highly concentrated, the pure amino-acid, both in 

 the case of glycocoll and of leucine, crystallised out first and that it was not till the mixture 

 was evaporated nearly to dryness, or by the addition of alcohol, that the neutral salt came 

 down also. Further evidence on this point is therefore necessary. 



On the other hand, there is certain evidence that salts are adsorbed by proteins. 

 Such effects as those on the temperature of coagulation are found to be expressed 

 by a formula similar to that of adsorption, and not by stoichiornetrical relations. 

 The amount of salt attached to the protein particle is found to be in certain pro- 

 portion to that free in the external phase. Pauli (1912, p. 231) also points out 

 that there is evidence that a surface action is in question, in that the viscosity 

 of protein solutions is always lowered by the addition of a salt. This implies 

 that the surface of contact is changed from one between albumin and water to one 

 between salt and water. 



If salts are adsorbed by protein, it is to be expected that, in the case of comparatively 

 insoluble salts, a considerable difference would be found in their apparent solubility in water 

 and in protein solutions. This has been found to be the case, by Pauli and Samec (1909, 

 p. 241), for calcium sulphate, phosphate and carbonate,, silicic acid and uric acid. The amount 

 of very soluble salts adsorbed would be too small a percentage of the total solubility to be 

 detected. 



Some experiments made by myself (1906, p. 182) on the rate of removal of salts from gelatine 

 by. water, also point to the adsorption nature of the union, as also other experiments on the 

 taking up of salts. 



A further fact in connection with the question before us is that measurements of electrical 

 conductivity show no effects of neutral salts similar to those which are so obvious where we 

 know that true chemical reaction takes place, viz., with strong acids and alkalies. 



The experiments of Bugarsky and Liebermann (1898, pp. 68, 72) show that 

 no combination occurs between proteins and neutral salts, whereas it does between 

 proteins and strong acids or alkalies. (See also page 221 below.) 



Chemical combination between neutral salts and proteins is, then, very 

 doubtful and cannot be used in explanation of observed facts unless directly 

 proved to take place. 



The fact that the effect of anions on the imbibition of water by starch and by 

 albumin is identical, as shown by Samec (1911, p. 154), is difficult to understand 

 on the assumption of a chemical union. 



That there are relationships of an electrical nature between proteins and ions, 

 apart from effects on the solvent or chemical reactions, is shown especially by the 

 work of Mines (1912, p. 217) with regard to the action of various ions on 

 emulsoids, inclusive of proteins. There is, in fact, an .action similar to that on 

 suspensoids or hydrophobe colloids. This latter we have already seen to be due to 

 electrical charges as such and it is natural to look for similar effects in the case of 

 proteins. Perhaps the most striking evidence in this connection is the behaviour 

 of the heart muscle, which will be better discussed in Chapter VII., under the 

 action of electrolytes in general. For the present, we may note that the heart of 

 the dogfish is 10,000 times more sensitive to various simple trivalent ions than to 

 the bivalent ion Mg- (p. 216). This extraordinary disparity between the effects 

 of two ions, not very different chemically, but whose electric charges are as 3 to 2, 

 shows distinctly that electrolytes have an effect on proteins or other emulsoids in 

 addition to the possible formation of salts, and that this effect is in relation 

 to their electric charges. This again being due to the adsorption by a surface of 

 ions of opposite charge to its own, will clearly depend on the sign and amount of 

 the charge of the protein particle; in water this charge is small as a rule, but 

 in acid or alkali, by the increased production of colloidal ions, the charge will be 



