106 PROCEEDINGS OF THE AMERICAN ACADEMY. 



nitrate thus prepared was concentrated by evaporation, and ammonia was 

 passed in until a mass of crystals of the blue ammonio-nickel nitrate was 

 formed. After the mother liquor had been poured off, the crystals were 

 washed with pure ammonia water, and were finally boiled in an excess of 

 pure water in the same platinum dish. The resulting basic hydroxide 

 was then changed to spongy nickel and nickelous bromide in the usual 

 fashion, bearing the title No. IV. 



Thus, while all of our samples of nickelous bromide analyzed had been 

 sublimed, the several samples had received previous to sublimation very 

 varying treatment. The fourth had been put through a process of puri- 

 fication far more searching than the first, which had merely been freed 

 from the ordinary known impurities. Hence the essential identity of 

 the results obtained from these several samples is very striking. 



Purification of other Materials. — Silver was purified exactly in the 

 manner described by Richards and Parker,* in a recent paper upon 

 the atomic weight of magnesium. The electrolytic crystals were finally 

 fused upon a boat of pure lime in a vacuum. For further details the 

 above mentioned paper should be consulted. 



With the co-operation of Mr. Baxter, bromine was purified in a pre- 

 liminary fashion by solution in strong aqueous calcic bromide, and a 

 subsequent separation. Carefully washed red phosphorus was used to 

 convert the bromine thus obtained, after it had been several times re- 

 distilled, into hydrobromic acid ; and the hydrobromic acid was freed 

 from iodine and organic matter by several fractional distillations with 

 bromine water. From this pure hydrobromic acid, bromine was obtained 

 by means of manganese dioxide free from chlorine. 2.10289 grams (in 

 vacuum) of silver yielded 3.66066 grams (in vacuum) of argentic bromide 

 on combination with this bromine, — a ratio of 57.445:100.00. Mr. 

 Baxter found 57.444 in a similar experiment, while Stas's value was 

 57.445 ; hence the purity of our bromine and silver was proved. 



Sodic hydroxide was freed from most metallic impurities (iron, etc.) 

 by electrolysis. Ammonia was redistilled in platinum vessels, as were 

 also nitric, and hydrochloric acids. Sulphuric acid was distilled in glass, 

 alkalies being a less dangerous impurity than platinum in the instances 

 where it was used. Water was purified by distillation first from alkaline 

 permanganate solution, and then with a trace of acid potassic sulphate. 



In processes where the presence of bromine rendered the use of pla- 

 tinum impossible, Jena glass, or at high temperatures Berlin porcelain, 



* These Proceedings, XXXII. 62. 



