584 



Mr. E. F. Burton on the Action of 



not the negatively charged sulphate ions, are the active ones 

 in bringing about the discharge of the particles. It was 

 further found that, not only was the charge of the particles 

 reversed, but at the point where the charge was zero, i. e. 

 at the point when the particles did not move in the electric 

 field (Hardy's isoelectric point), the solutions showed a mini- 

 mum stability. For example, to refer to a table taken from 

 the former paper, two samples of a gold solution to which 



Table I. 

 Gold Colloidal Solution. 



No. 



Grins. Al added 

 per 100 ccs. sol. 



Specific Conduc- 

 tivity at 18° C. 



Velocity of the 



particles in 



crns./sec./ volt/cm. 



1. 

 2. 

 3. 

 4. 





 19X10" 6 

 38X10" 6 

 63xl0" 6 



3-GxlO- 6 



5-2X10" 6 



6-6xl0" 6 



11-6X10 -6 



*-33xl0~ 5 

 -17-lXlO" 5 

 +1-7X10" 5 

 +13-5X10 -5 



* In this table, as in all succeeding ones, the + sign denotes motion 

 toward the cathode, the — sign toward the anode. 



were added respectively 19xl0~ 6 and 38xl0 -6 grm. of 

 aluminium per 100 ccs. coagulated at the end of a few hours, 

 while another sample of the same solution, to which 63 X 10 ~ 6 

 grm. per cc. were added, did not completely coagulate at the 

 end of four days. As a result of this work we have strong- 

 evidence as to the validity of the assumption that, in these 

 solutions at least, coagulation is brought about through the 

 discharge of the colloidal particles by the ions of the electro- 

 lyte introduced into the colloidal solution, and that the 

 deportment of the Bredig metallic colloidal solutions is 

 similar to that which Hardy found displayed by his specially 

 treated albumen solutions. 



2. PUKPOSE OF THE EXPERIMENTS. 



The results given below may be viewed as an instalment of 

 a systematic investigation on the effect of various electrolytic 

 solutions on the velocities of colloidal particles in an electric 

 field, and consequently the effect on the size and sign of the 

 charge possessed by those particles. Copper colloidal solution 

 has been selected because its particles are positively charged, 



