M. 0. Lea — Gold-colored Allotropic Silver. 183 



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-colored 

 product is less pure. A beautiful steel-blue substance obtained 

 in this way was found to contain a considerable quantity of tin, 

 probably present as stannic oxide, 10*87 per cent of tin corres- 

 ponding to 13*80 Sn0 2 was found by analysis. Another analy- 

 sis 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 process gave far better results, the examination was 

 not carried farther. Silver citrate gives similar results. 



Action of different forms of Energy on Allotropic Silver. 

 ]. Action of Electricity. 



High tension electricity instantly converts gold-colored sil- 

 ver to the ordinary form. "When paper covered with a film of 

 gold-colored silver is held between the conductors of a Topler- 

 Holtz machine, each spark forms a gray 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 color contrasts with the 

 purplish shade of the spark. 



When several pieces are in this way held between the con- 

 ductors together, there is a transfer of silver from one piece to 

 the other, so that the back of each piece of paper is blackened 

 by silver carried over from the one behind it. 



That the branching gray spots in this way formed, are nor- 

 mal silver, is easily proved by immersing the piece in a dilute 

 solution of potassium ferricyanide. The part acted upon by 

 electricity is not affected by the reagent, while the rest of the 

 film shows the coloration characteristic of allotropic silver. In 

 Plate I the upper figure shows a slip of paper, at one end of 

 which electricity has been transmitted, and the figure below, a 

 similar slip that has been subjected to the action of the fer- 

 ricyanide, showing that where electricity has passed the silver 

 has become normal and is not affected by the reagent. 



