J. C. Blake— Colloidal Gold. 385 



Hence, it appears that adsorption phenomena are not pro- 

 nouncedly concerned, if at all, in the color changes brought 

 about in red gold solutions by electrolytes, or in the subsequent 

 precipitation of the blue or of the spongy gold. Some inter- 

 esting results might be obtained in this connection by working 

 with neutral red gold solutions, such as might have been pre- 

 pared by dialysing the ones here described ; but it is difficult 

 to see how any such results could be intelligible unless differ- 

 entiated by a series of parallel experiments from the effects 

 due to the hydrolysis of neutral salts and absorption of the 

 basic radical by porous solids. If these two effects are identical, 

 as suggested by Whitney and Ober, then Whetham's hypothe- 

 sis can receive no support from the results to be obtained with 

 them. 



The " blue gold " precipitated in these experiments is amor- 

 phous and has a dark bronze appearance when viewed in 

 reflected light. The three apparently allotropic forms of gold 

 here noted, named according to the colors most readily ob- 

 served, as in the case of silver,* are the following : 





Color in 



Color in 



Form of gold. 



reflected light. 



transmitted light. 



"Yellow gold" 



Golden 



Blue 



"Blue gold" 



Dark bronze 



Blue 



"Red gold" 



Light goldenf 



Red 



* This Journal [4J, xvi, 282 (1903). 

 f Well seen in the Tyndall effect. 



Am. Joue. Sci. — Fourth Seeies, Vol. XVI, No. 95. — November, 1903. 

 27 



