242 Mr. M. Carey Lea on 



Substances of a character nearly related to those that I 

 have described in this and the previous paper, are obtained 

 by acting on silver tartrate with stannous nitrate. The 

 method is more troublesome and gives inferior results, the 

 gold-coloured product is less pure. A beautiful steel-blue 

 substance obtained in this way was found to contain a con- 

 siderable quantity of tin, probably present as stannic oxide ; 

 10*87 per cent, of tin corresponding to 13*80 Sn0 3 was 

 found by analysis. Another analysis gave 10'66 per cent., 

 corresponding to 13*61 Sn0 2 . In the first case, the quantity 

 of silver found was 83*61, in the second 84*12 per cent. 

 These results do not lead to any satisfactory formula. The 

 tin is no doubt present as an impurity, and as the iron pro- 

 cess gave far better results, the examination was not carried 

 further. Silver citrate gives similar results. 



Action of Different Forms of Energy on 

 Allotropic Silver. 



1. Action of Electricity . 



High-tension electricity instantly converts gold-coloured 

 silver to the ordinary form. When paper covered with a 

 film of gold- coloured silver is held between the conductors of 

 a Topler-Holtz machine, each spark forms a grey dot of 

 ordinary silver. A powerful discharge is not necessary ; an 

 inch spark from a small machine is effectual, even when the 

 condensers are cut off. There is also a lateral action, which 

 is best seen when several slips of such paper are held loosely 

 together and placed between the conductors. When the 

 slips are opened a little, the lateral branches are beautifully 

 seen, playing through the silver. Their fine emerald-green 

 colour contrasts with the purplish shade of the spark. 



When several pieces are in this way held between the 

 conductors together, there is a transfer of silver from one 



In another vessel are placed : — 



Water 800 c.c. 



20-per-cent. sol. Rochelle salt 200 „ 



30-per-cent. sol. ferrous sulphate (crystallized) .... 107 „ 



(The substances must be added in the order above given, and be mixed 

 immediately before using. It is scarcely necessary to say that distilled 

 water must be used exclusively.) As soon as the mixtures are made the 

 iron solution is to be poured into the silver and vigorously stirred for some 

 time. The white silver tartrate becomes almost immediately bright red, 

 then deepens in colour, and finally becomes black. 



