270 CHEMISTRY OF THE PROTEIDS CHAP. 



Cassius, which is a hydrosol of stannic acid and gold are thrown 

 down together by electrolytes having the opposite electrical load. 

 He also found that the precipitating action of mixtures of electrolytes 

 and colloids is an additive effect, and that in many cases an action 

 which seems to be brought about by an electrolyte is caused at least 

 partly by the presence of colloids. In this connection he draws atten- 

 tion to the work of Spring, 1 who showed that solutions of the salts of 

 plurivalent metals (such as aluminium chloride or ferric chloride) are 

 not optically void, and therefore must contain colloidal hydroxide ; 

 and also to the work of Mylius, 2 who accounts for the fact that meta- 

 phosphoric does, while orthophosphoric does not, coagulate albumin by 

 showing that metaphosphoric acid contains polymolecular particles, i.e. 

 that it is in fact a ' colloidal ' solution. Mylius further shows that 

 all acids which precipitate ordinary white of egg, after it has been 

 diluted, contain complex molecules. 



Biltz objects to a chemical explanation of colloidal solutions, and 

 considers Bredig's view to be correct, namely, that the cause of the 

 relatively great stability of pure colloidal solutions is the electrical 

 difference of potential between the colloid and the solvent. The author 

 wishes to point out that according to all laws of physical chemistry 

 the first essential for chemical interaction is the establishment of an 

 electrical load, or, in other words, that only those substances which 

 carry an electrical load are capable of acting upon one another 

 ' chemically.' To say, as does Biltz, that we are dealing with 

 adsorption-phenomena when a colloid is precipitated, is not giving an 

 explanation at all, but amounts simply to stating the premise over 

 again in a roundabout manner. If the cause of the adsorption is the 

 ionic difference of potential between two substances, then adsorption 

 means simply chemical union. 



The inter-relation of suspensions and colloids in viscid media ; the 

 behaviour of colloids upon one another, and how under certain circum- 

 stances one colloid may prevent the precipitation of a second colloid, 

 are fully discussed by Arthur Miiller. 3 



Whitney and Ober 4 were able to show that different metals com- 

 bine in equivalent amounts with colloids in forming precipitates, 

 thus : 



1 Spring, Bull, de I'Acad. Roy. de Belg. 1900, p. 483. 



2 F. Mylius, Ber. d. deutsch. chem. Ges. 36. 775 (1903). (The reader's attention is 

 especially directed to this important paper.) 



3 Arthur Miiller, ibid. Ges. 37- 11 (1904). 



4 Whitney and Ober, Zeit. f. physik. Chem. 39. 630 (1902). 



