Electrolytes on Copper Colloidal Solutions. 597 



Is suported by Lottermoser's criticism o£ Duclaux's work, in 

 which the former constantly refers to a class of colloids 

 which can be changed by the addition of certain electrolytes 

 from hydrosols to hydrogels and vice versa ; whereas in no 

 case have the metallic colloids at present under discussion 

 shown that they are thus reversible. 



Exception must be taken, however, to the remark of 

 Duclaux when he says that " it is by no means evident that 

 the immobility of a micelle in an electric field implies that 

 the micelle does not carry a charge." Historically, the 

 only reason we have for attributing the possession of a charge 

 to the colloidal particle is the fact that it does move in an 

 electric field, and, if dependence is not to be placed on this 

 assumption, there is no ground for speaking of the particles 

 as being charged at all. If we mean anything by the 

 statement that a colloidal particle is positively or negatively 

 charged, it is surely a just conclusion to say that, if the 

 particle does not move in an electric field, it has lost its 

 charge. 



6. Conclusions. 



1. For a copper colloidal solution, the particles of which 

 are positively charged (i: e. move to the cathode), the influence 

 of added electrolytes on the velocity of the particle has been 

 determined. The electrolytes used were potassium chloride, 

 potassium phosphate, potassium sulphate, potassium ferri- 

 evanide, and aluminium sulphate. 



2. Evidence has been produced to show that it is the ion 

 bearing a negative charge that is active in reducing the 

 velocity. 



3. This power of the negative ion depends on the valency 

 in a way analogous to the valency relations found by Picton 

 and Linder, and by Hardy, for the coagulative power 

 of ions. 



4. The discharging power of two negative ions of the same 

 valency is the same. 



5. Observations on the coagulation produced in each case 

 shows that the particles coagulate when they lose their 



In conclusion, I wish to thank Professor J. C. McLennan 

 for his kind assistance and encouragement at all times ; I also 

 desire to express my indebtedness to Professor A. B. Macallum 

 for his helpful suggestions on many occasions. 



University of Toronto, 

 November 2nd, 1908. 



