596 Mr. E. F. Burton on the Action of 



on aluminium sulphate were not carried out as far as those 

 on potassium sulphate, nevertheless the corresponding curves 

 show a remarkable coincidence in the region common to the 

 two curves. 



These latter two curves have an additional importance in 

 that they show that the action of the SO4 ion is practically- 

 independent of the metal ion. Since aluminium is trivalent 

 and potassium monovalent, i£ the metal ions exerted any 

 marked influence on the copper particle we should expect 

 these two curves to be very far apart. 



Again, comparing the five curves, one has the very 

 strongest evidence of the great differences in the powers of 

 monovalent, divalent, and trivalent acid ions to reduce the 

 velocity of the positively charged copper, and consequently, 

 to produce coagulation. Examination of the curves will 

 show that the velocity results indicate that the ratios of the 

 powers of various acid ions to reduce the velocity of the 

 copper particles are not very far removed from the observed 

 ratios of the powers of the same ions to produce coagulation. 

 These latter ratios for monovalent, divalent, and trivalent ions 

 as found by Picton and Linder * were 1 : 35 : 1023 ; the- 

 analogous ratios suggested in accordance with Whetham's- 

 theory f of coagulation were 1 : 32 : 1024. 



Some time since Duclaux published results of his work 011 

 colloids synthetically prepared by a double decomposition, 

 as, for example, the colloidal solution of copper ferrocyanide 

 resulting from the action of cupric chloride (CuCl 2 ) on 

 potassium ferrocyanide. In this case he finds that the 

 colloidal particle retains varying quantities of the potassium, 

 to which he gives the credit for the existence of the colloidal 

 particle. This portion of the colloidal unit he calls the 

 " partie active," and draws the conclusion that the coagulation 

 of the colloid is brought about through the substitution of 

 the " partie active " by some other ions. In the course of 

 his argument, he expresses " most formal doubts as to the 

 exactitude of Hardy's law according to which the coagulative 

 power of an ion is the greater, the higher its valency." The 

 law of Hardy referred to above is based on the experimental 

 work of Picton and Linder and others, as well as that of 

 Hardy himself, and is uniquely supported by the theoretical 

 contribution of Whetham. The conclusions arrived at by 

 Duclaux seem so diametrically opposed to all this work, as 

 to suggest the possibility that Duclaux was dealing with 

 colloidal solutions quite different in their constitution from 

 those upon which the above law was based. This conclusion 



* Loc. cit. t ' Theory of Solution/ p. 396. 



