440 Blake — Behavior of Red Colloidal Gold Solutions. 



paring gold hjdrosols (aqueous colloidal solutions), served to 

 bring about the desired result.f Hence the following experi- 

 ments were made in order to find out, if possible, whether 

 electrical phenomena were demonstrably concerned in bring- 

 ing about the change of color. In the experiments given 

 under A of Table lY a red colloidal gold solution containing 

 0'0193 gram of gold per liter was titrated with electrolytes 

 without the presence of the current, for purposes of compari- 

 son ; in those given under B the titration was made in the 

 presence of electrodes of platinum wire at a potential dif- 

 ference of 110 volts and O'S'^™ apart. In these experiments 

 the first noticeable change of color of the liquid from red to 

 purple was taken as the end-point. Under these conditions 

 the liquids included under A, as Avell as those titrated with 

 sodium sulphate under B, assumed a distinct purple or violet 

 color vrithin ten minutes after the titration was completed, but 

 the gold remained suspended for some days, finally settling in 

 the form of a purple or violet powder. The liquids titrate 

 with potassium alum in the presence of the current changed 

 from purple to blue almost at once. 



Table IY. 



Volume of gold solution, 100'="^^. 

 A. Titrated without the electric current. 



Electrolyte. 



n 



Too 



■KA1(S0J,.12H,0 



^-Na,SO, 



Amt. 





of 





elect. 



Aver- 



cm^. 



ages. 



3-19 





2-90 



3-01 



2-95 





15-8 





16-4 16-3 



17-2 





Final concentration of 

 electrolyte in terms 

 of normal strength. 



. 1 Q^rara mol. 



'00029 of -^ per hter 



B. Titrated in the presence of the electric current. 



j^-KAl(S0J,.12H,0 

 n - Na.SO. 



1-36 





1-45 



1-35 



1-25 





20-4 





18-2 



20-1 



21-8 





„ 1 o-ram mol. ,. 

 00013 of ^^ — i perhter 



167 of 1 gram mol. per liter 



These results are sufiicient to show that the phenomena 

 involved in the titration of red gold solutions with electrolytes 

 in the presence of the electric current are complex and demand 



*Cf. Spring, loc. cit. 



