404 PROCEEDINGS OF THE AMERICAN ACADEMY. 



vious researches in this laboratory. A large quantity of heterogeneous 

 silver residues were reduced to metallic silver by means of sticks of pure 

 zinc in slightly acid solution. After the silver had been washed with 

 water until free from halogens, it was dissolved in nitric acid, and the 

 solution was filtered. Silver chloride was precipitated from the diluted 

 nitrate by means of hydrochloric acid, and the precipitate of silver chlo- 

 ride was thoroughly washed. From this silver chloride, metallic silver 

 was again obtained by reduction with cane sugar in strongly alkaline 

 solution. After being washed until free from chloride, the metal was 

 again dissolved in nitric acid in a Jena glass flask. By reduction with 

 amnionic formate (prepared from redistilled formic acid and redistilled 

 ammonia), the silver was once more obtained in the metallic state. The 

 beautiful mass of crystals was then dissolved in the purest nitric acid, 

 and the nitrate, after concentration of the solution, was four times re- 

 crystallized from the purest water in platinum until free from acid. In 

 this crystallization, and in all others, centrifugal drainage in a machine 

 employing platinum funnels as baskets 16 was always used, in order to 

 free the crystals entirely from any adhering mother liquor, the mother 

 liquors all being rejected. 



Hydrochloric Acid. — Hydrochloric acid was prepared by distilling 

 the commercial chemically pure acid, after dilution with an equal 

 volume of water. 



Hydrobromic Acid. — The methods for obtaining pure bromine have 

 been recently tested by one of us, 17 and the processes found suitable for 

 the purpose were employed here. A considerable quantity of hydrobro- 

 mic acid was prepared by passing a current of pure hydrogen sulphide 

 through a layer of bromine covered with water. The hydrogen sul- 

 phide was generated by the action of dilute sulphuric acid on ferrous 

 sulphide, and was thoroughly scrubbed in gas washing bottles and towers 

 containing water. After the precipitated mixture of sulphur bromide 

 and sulphur had been removed by decantation and filtration, the acid 

 was boiled* with the occasional addition of small portions of recrystal- 

 lized potassium permanganate. This was done to eliminate any iodine 

 which might have been present. 



The hydrobromic acid was then heated with the calculated quantity 

 of recrystallized potassium permanganate, the bromine being condensed 

 in a Jena flask cooled with running water. In this way three eighths of 

 the bromine remained behind as potassium and manganous bromides, 

 the remaining five eighths beinjj distilled from the solution of these bro- 



16 Richards, Jour. Amer. Chem. Soc, 27, 110 (1905). 

 " Baxter, These proceedings, 42, 20-1 (1906). 



