Blake — Behavior of Red Colloidal Oold Solutions. 439 



Table III. 

 Volume of gold solution, 50°™^. 



Volume 

 ratio of 





^-KaAl- 



Aver- 



Final concentration 



ether 

 added. 





(S04)2.12H20 



em^. 



ages, 

 cm^. 



of electrolyte in terms 

 of normal strength. 







1-8 











1-7 



1-9 



1-8 



•00035" 









1-9 













2-58 









1:50 





2-65 

 2-50 

 2-10 



2-61 



■00050 





1 :25 





3-15 

 3-05 

 3-35 



3-18 



•00060 



Igrammol. ,. 



r 01 -^ — per liter 



3 



Saturated, 













exposed to 

 air during 

 titration. 



\ 



5-00 



5-00 



•00091 





Saturated, 











titrated 

 under 



8-75 

 9-20 



8-98 



•00151 





ether. 



J 









In the last two experiments of the table neither alnmininm 

 nor sulphnric or hydrochloric acid conld be fonnd in the ether. 

 Hence it appears that the presence of the ether tends to inhibit 

 the action of electrolytes to snch an extent that a red gold solu- 

 tion kept saturated with ether by a su|)erim posed layer of it 

 required more than four times as great a concentration of the 

 potassium alum to produce the change of color as was required 

 by a solution containing the same amount of gold and acety- 

 lene and but very little ether. The effect, if any, of varying 

 the amounts of gold and acetylene is covered up by the simul- 

 taneous variations produced by changes in the amount of ether 

 present. 



Since it was found impossible to turn red colloidal gold solu- 

 tions blue in the experiments with the electric current detained 

 at the beginning of this paper, other electrical means of bring- 

 ing about the change of color were sought ; but neither the 

 alternating current from an induction coil, giving an inch 

 spark in air, nor long-continued sparking between gold elec- 

 trodes with the direct current, as in Bredig's^ method of pre- 



*Loc. cit. Zeit. angew. Chem., 1898, p. 951 ; Bredig and Eeinders, Zeit. 

 Phys. Chem., xxxvii, 323, 



