D. CHEMISTRY AND METALLURGY. 205 



of recovering the metallic zinc so as to be re-employed in a 

 continuous process, has been again brought into operation at 

 Tarnowitz, in Silesia. The argentiferous zinc crust is now al- 

 lowed to cool in an iron basin, then placed in the liquating fur- 

 nace, where, by gentle heating, with full access of air, it is de- 

 prived of the greater part of its lead. By this means the 

 zinc is thoroughly oxidized and converted into the so-called 

 zinc dust, which is then distilled betAveen layers of powdered 

 coke, with the production of metallic zinc, free from silver, 

 on the one hand, together with a residue containing the whole, 

 of the silver, along with any lead remaining in the zinc dust. 

 18 A,A2Jril 9, 1875, 89. 



ON THE FUSIBILITY, ETC., OF ALLOYS OF SILVER AND 



COPPER. 



Mr. Roberts, chemist to the English Mint, has communi- 

 cated to the Royal Society the result of a detailed elaborate 

 investigation into the liquidation, fusibility, and density of 

 certain alloys of silver and copper. The melting-point of 

 the several alloys experimented upon by him varied from 

 840 Centigrade to 1330 Centigrade, the most fusible alloys 

 being those that contain from sixty to seventy per cent, of 

 silver ; and the fusibilities vary very much as to the electric 

 conductivities. The density of pure silver, when fluid, is 

 9.46; its density when solid is 10.57. This alloy, therefore, 

 on becoming fluid, expands at nearly double the rate that it 

 expands when at ordinary temperatures. Mr. Roberts has 

 also succeeded in obtaining excellent results in the electro- 

 deposition of iron, for which purpose he employs a solution 

 of the double sulphate of iron and magnesia. The iron thus 

 obtained possesses a higher electric conductivity than any 

 commercial iron, and occludes thirteen times its volume of 

 liydrogen. The tube of the metal, which was a vacuum tried 

 at the ordinary temperature, allowed hydrogen to pass 

 through it freely at a dull red heat. 



A NEW TEST FOR GOLD. 



M. Sergius Kern, of St. Petersburg, in studying the be- 

 havior of certain double salts of gold, made the observation 

 that the sulpho-cyanide of potassium was a most sensitive 

 reagent of this metal, which, as experiment proved, would 



