Blake — Behavior of Red Colloidal Gold Solutions. 441 



extended investigation. Thus the presence of the electric cur- 

 rent increased the activity of the potassium akim, but retarded 

 that of the sodium sulphate. Since the acid radicals were the 

 same, it is necessary to attribute the difference in behavior to 

 the basic radicals, thus strengthening the belief that the basic 

 radical is the active factor in causing precipitation when the 

 current is not acting. In one experiment with a hundredth- 

 normal solution of j)otassium alum, it was found that the 

 amount of electrolyte required to turn the red solution blue 

 was not changed by the passage of the current under the same 

 conditions as before for ten minutes and subsequent titration 

 after the current was broken. This supports the conclusion 

 arrived at above (p. 435) that red colloidal gold solutions are not 

 necessarily permanently affected by the passage of the electric 

 current. 



The separate coagulation and precipitation of red gold solu- 

 tions and the separate coagulation and precipitation of blue 

 gold solutions, as well as the reverse change of color from blue 

 to red with its apparent hysteresis, are being studied further. 

 The fact that these gold solutions show five different effects on 

 the addition of electrolytes, instead of two as in most col- 

 loidal solutions, renders them exceedingly interesting from a 

 theoretical standpoint. Until the activity of electrolytes in 

 bringing about each of these effects is better understood and 

 differentiated, it would seem that speculation with regard to 

 the causes which induce them would be idle ; for in the 

 process of turning red solutions blue as ordinarily conducted 

 all live phenomena are doubtless involved. Some results 

 obtained by titrating the same gold solution first to the purple 

 color, then immediately to the violet color, are given below. 

 The fact (noted above) that in the former case the gold settles 

 slowly in the form of a purple or violet powder, in the latter 

 case in the form of a blue powder and at the maximum rate, 

 indicates that within the limits between the two readings is 

 included the entire range of concentration of the electrolyte 

 necessary to increase to the maximum the rate of subsidence of 

 the red gold, to complete the change of color from red to blue, 

 and to precipitate the blue gold thus formed. 



Table V. 



Volume of gold solution, SO'^'"^ Electrolyte, ~ KAKSOOa.l^HaO. 

 Titrated to purple. Titrated to violet. 



2-25 

 2-45 

 2-50 



3-65 

 3-40 

 3-45 



2-40 y 2-41 3-45 } 3*49 



2-70 

 2-30 

 2-30 



3-55 

 3-50 

 3-40 



