Coagulative Power of Electrolytes. 475 



This coagulative action is of interest in certain physiolo- 

 gical inquiries; and it was in connexion with some physio- 

 logical work by Mr. W. B. Hardy* that the following 

 suo-o-estion originated. The matter, however, seems also to 

 have some bearing on the theory of the physical nature of 

 electrolytic solutions. 



The coagulative power of a substance may be taken to be 

 inversely proportional to the number of gram-equivalents 

 which must be added to a definite solution of the colloid in 

 order that immediate coagulation should follow- Thus, 

 according to the experiments of Linder and Pictonf, the 

 numbers expressing the concentrations of equi-coagulative 

 solutions of various sulphates, when acting on arsenious sul- 

 phide, range round the following mean values for monovalent, 

 divalent, and trivalent ions, the figure for aluminium chloride 

 being taken as unity: — 



930 : 2(3 : 0'9. 

 The relative coagulative powers would be proportional to the 

 reciprocals of these numbers, which are in the ratios 

 1 : 35 : 1023. 



Again, Schulze \ found for solutions of chlorides coagulative 

 powers in the ratios 



1 : 30 : 1650. 



These numbers are enough to show that the valency of the 

 metallic ion has an effect on the coagulative power very 

 different from that on properties for which the usual 1:2:3 

 ratios hold good. 



The coagulative powers of salts are certainly intimately 

 connected with their electrical properties (see Hardy, I. c.) ; 

 and an explanation of the curious valency relations must be 

 sought by the light of our knowledge of the electrical nature 

 of solutions. 



Let us suppose that, in order to produce the aggregation of 

 colloidal particles which constitutes coagulation, a certain 

 minimum electrical charge has to be brought within reach of 

 a colloidal group, and that such conjunctions must occur with 

 a certain minimum frequency throughout the solution. Since 

 the electrical charge on an ion is proportional to its valency, 

 we shall get equal charges by the conjunction of 2n triads, 

 '6n diads, or 6n monads, where n is any whole number. 



In a solution where ions are moving freely, the proba- 

 bility that an ion is at any instant within reach of a fixed 

 point is, putting certainty equal to unity, approximately repre- 

 sented by a fraction proportional to the ratio between the volume 



* Journal of Physiology, xxiv. p. 288 (1899). 

 t Journ. of the Cheni. Soc. lxvii. p. 63 (18%\ 

 % Journ. f. Prakt. Chem. xxv. p. 431 (1892>. 



