COLLOIDAL METALS. 



53 



normal silver in a finely divided state, little if any being in true solution 

 (molecularly subdivided). He further concludes that the color of ruby 

 gold glass is due primarily to the presence of small spheres of gold; the 

 irregular blue and purple colors, sometimes exhibited by gold glass, are 

 then explained by the presence of crystallites (caused by the coagulation 

 of gold spheres) which reflect but do not transmit red light. 



100% 



90 



80 



70 



60 



C 



o 



if) 50 



'e 



It) 



30 



20 



10 



d^ {Au (Colloidal) 



.5 / 2 3 



Fig. 36. Gold; Silver; Nickel. 



In view of the fact that colloidal metals appear to behave exactly the 



reverse of films of a metal in the normal state, the subject deserves further 



consideration. 



Gold and Nickel. 



In fig. 36, curve a gives the transmission (Hagen and Rubens, loc. cit.) 

 of a metallic film of gold, which has the well-known transmission band in 

 the yellowish-green part of the spectrum. Curves c and d give the trans- 

 mission of suspensions, in water, of colloidal gold and nickel, respectively, 

 studied photometrically by Ehrenhaft. 1 The gold transmitted red, while 

 nickel (also Pt and Co) have a brown color by transmitted light. As in 

 the present work, the behavior of the colloidal material is exactly the 

 reverse of the normal metal film, thus placing it under the class known as 

 non-metals or " insulators." 



1 Ehrenhaft: Ann. der Phys., II, p. 489, 1903. 



