RICHARDS AND ROGERS. — ATOMIC WEIGHT OF ZINC. 171 



The solution of the last crystals was allowed to stand for two days 

 over several grams of the purest crystalline electrolytic ziuc in a 

 large platinum dish. At the end of that time the solution contained 

 some basic salt, but the dish showed no sign of a metallic coating. 

 The solution was filtered, treated with an excess of freshly distilled 

 ammonia, and electrolyzed. A thin rod of very pure zinc served as 

 the negative pole, and a platinum wire as the positive. Six decom- 

 posing cells were run simultaneously on a shunt from a fifty-volt 

 dynamo which was being used for charging a storage battery. The 

 current in each decomposing cell varied from one to one and a half 

 amperes, — if a much stronger current was used the cells became too 

 warm. As Ramsay and Reynolds * have suggested, it is advisable to 

 remove the remarkably beautiful crystals from time to time as they 

 grow ; for this purpose a bent five-pronged glass fork made from a 

 heavy rod was found very useful. The crystals were washed with 

 ammonia until the washings were absolutely free from sulphuric acid, 

 then with ^^ure very dilute hydrobromic acid, and finally with much 

 pure water. About forty grams of pure zinc thus formed were treated 

 with an excess of pure bromine, which had been shaken with an alka- 

 line bromide in aqueous solution, dissolved in concentrated calcic 

 bromide, precipitated by water, and distilled under dilute pure hydro- 

 bromic acid. The Jena glass flask in which the combination took 

 place was cooled during the reaction. The red solution was filtered 

 in a glass funnel through asbestos, and the excess of bromine, together 

 with any trace of iodine which may have been present, was driven off 

 by leaving the Jena flask upon the steam bath for some time in a very 

 much inclined position. The diluted colorless solution was evaporated 

 to small bulk, and the greater part of it was subjected to fractional 

 crystallization by cooling to zero. A portion which had crystallized 

 twice successively, from water was labelled (A), and another portion, 

 the extreme mother liquor remaining from two crystallizations was 

 labelled (C). Sample (B), the intermediate fraction, was not used in 

 these experiments, as (A) and (C) were proved to be identical. 



Before analysis both (A) and (C) were subjected either to distillation 

 or to sublimation. Tlie sublimation was carried on in the lower part 

 of a platinum retort, to which had been fitted closely a glass adapter 

 for conducting the current of pure dry carbon dioxide. The substance 

 to be sublimed was contained in a small platinum crucible fitted with 

 a wire handle, by which it could easily be raised, lowered, or removed. 



* Loc. cit. 



