240 M. Carey Lea — Properties of Allotropic Silver. 



and iodine compounds. In some earlier experiments I ob- 

 tained effects of the same sort, but in much weaker degree 

 with alkaline haloids. But with purer products, the results 

 have been different. There is at first some darkening, but no 

 true color reaction and the allotropic silver appears to be 

 gradually converted into normal, so that it is no longer capable 

 of giving the brilliant color reaction with potassium ferrid- 

 cyanide, but, like normal silver, takes a pale and faint colora- 

 tion only. 



The perchlorides of platinum, gold and tin do not give the 

 color reaction, though by analogy one would expect that they 

 should, since they can lose chlorine with formation of a lower 

 chloride. 



Action of Light. — In a previous paper was mentioned the 

 remarkable fact that the gold- and copper- colored forms of 

 allotropic silver can be converted first into yellow and finally 

 into white normal silver by the continued action of light. 

 The earlier specimens of the blue form became brown by 

 exposure, but purer ones since obtained are likewise converted 

 into yellow by exposure, becoming continually lighter as the 

 action is continued. The conversion from the darker shades 

 to a bright yellow with full metallic luster is very easy, but 

 when the previous paper was written I had been only able to 

 obtain the white by keeping the paper, on which the silver was 

 coated, moist by a wet pad and by exposing for five or six 

 days. Since then I have obtained the gold-colored silver in a 

 more sensitive form, giving a perfectly white product by 

 exposure dry for half that time. 



The white silver thus obtained has all the character of 

 ordinary silver and does not show the color reaction with 

 ferric and cupric chloride, potassium ferridcyanide, etc. Just 

 in proportion to the exposure to light, the ability to give this 

 color reaction diminishes, so that after a day's exposure, when 

 the exposed part has become bright yellow, the color reagents 

 scarcely affect this yellow, whilst the protected part becomes 

 intense blue, purple, or green. In this way it is easy to 

 observe the gradual effect of light as it changes the allotropic 

 silver, finally converting it into what resembles in every way, 

 and is undoubtedly, ordinary silver. 



July, 1889. 



