Blake — Behavior of Bed Colloidal Gold Solutions. 437 



Table I. 



Vol. of 



gold 

 solution 



50 

 50 



50 

 50 

 50 



50 

 50 

 50 

 50 

 100 



50 



50 



50 



100 



50 

 100 



20 



Electrolyte. 



n 



To" 



n 

 100 



-KA1(S0J,.12H,0 

 -KA1(S0,),.12H,0 



-BaCl, 



-Ba(N03), 



-NaCl 

 - NaCl 



Amt. 



Of 

 elect, 

 cm^. 



Aver- 

 ages for 



5Qcm3_ 



0-4 

 0-4 



0-4 



2-1 





2-2 

 2-2 



2-2 



2-8 





3-3 





3-2 



3-11 



30 





6-5 





3-4 





3-7 



3-45 



3-3 





6-8 





7-7 



7-6 



15-0 





100 





Final concentration of 

 electrolyte in terms 

 of normal strength. 



■0008 of 



■0004 of 



0058 of 



0064 of 



1 gram mol. 

 3 

 per liter. 



1 gram mol. 



3 

 per liter. 



1 gram mol. 



2 ^- 



per liter. 



1 gram mol. 



2 

 per liter. 



•13 of 1 gram. mol. 

 per liter. 



•083* of 1 gram mol. 

 per liter. 



These results are in accord with Whetliam'sf hypothesis, 

 that the activity of electrolytes toward colloidal solutions is an 

 exponential function of the valency of the basic elements 

 which they contain, the final concentration of sodium chloride 

 necessary to induce tlie change of color from red to blue being 

 22*4 times that of barium chloride, which, in turn, is 14^5 that 

 of potassium alum. I^o amount of a tenth-normal solution of 

 sodium chloride brings about the change of color within a 

 reasonable length of time (see the last experiment of the table), 

 the final concentration required, •18-normal, being greater than 

 that of a tenth-normal solution. The fact that the change of 

 color takes place suddenly at a given concentration of the 

 electrolytes and that a weaker concentration of the same elec- 

 trolytes does not produce the change of color even after a con- 

 siderable lapse of time, tends to disprove the hypothesis of 

 Whetham, since time should be an active factor in bringing 



* Solution not turned blue in two days. 



f Jour, of Physiol., xxiv, 288; Phil. Mag., xlviii, 474. 



