FOR ELECTRIC RUBBERS, 157 



tals are found to extend higher up upon the rod. During the 

 process a considerable portion of the sulphur is sublimed and 

 escapes. The period for withdrawing the crucible from the 

 fire is known by the sublimation of the sulphur ceasing and 

 the depth of the crystalization upon the rod, when withdrawn. 

 The great difficulty it occurs to me, is to avoid giving too high 

 a heat — by carefully watching and regulating the heat I have 

 succeeded in obtaining a sulphuret, admirably adapted for 

 electrical rubbers. This which is now submitted was prepared 

 in two hours. If the crucible be allowed to cool very slowly, 

 much more brilliant crystals are procured having all the lustre 

 and beauty of gold. This process is evidently a great im- 

 provement over the old method which required several hours 

 for its completion. I have generally used an open furnace for 

 this preparation, and have succeeded in regulating the heat of 

 a charcoal fire without difficulty. Dr. Edmondson informs 

 me that he succeeded with a spirit lamp, in obtaining some 

 very fine mosaic gold, and 1 have seldom seen handsomer 

 than that which he employs. The smaller crystals are more 

 mutuous and adhere more readily to the rubbers than the 

 larger, which enables us to present a greater surface of metallic 

 coating to the cylinder or plate, they are consequently prefe- 

 rable for electrical purposes. 



The Amalgam, used as a substitute for mosaic gold, is 

 made from two parts mercury, one part tin, and one part zinc. 

 The zinc is first melted in an iron ladle or crucible, the tin 

 then added, which readily fuses in the melted zinc, and then 

 the mercury. The proportions of this mixture are such as to 

 form a crystalized alloy or amalgam, when the melted mass 

 is poured out upon a sheet of iron or other cooling incombus- 

 tible. To avoid misapprehension, it seems proper to add, that 

 neither of the mixtures described, is original with myself. 

 The former is from Turner's Chemistry, and the latter from 

 Brewster's Encyclopedia, Art. Electricity. It is recommended 

 by Baron Keinmayer, who found that with the common amal- 

 gam, he could charge a liCyden vial having 1 \ square feet of 

 coated surface with ten revolutions, whereas, with the amal- 

 gam which he recommends, he required only six. A battery 

 consisting of 53 square feet of coated surface, required 250 

 revolutions with common amalgam, whereas with the new 



