RICHARDS AND ROGERS. — ATOMIC WEIGHT OF ZINC. 165 



was allowed to act upon the phosphorus and water with the usual pre- 

 cautious in an apparatus made wholly of glass. The acid thus formed 

 was distilled in five fractions, of which the first consisted chiefly of 

 water and a trace of bromoform. Only the last fraction of the distil- 

 late containing perhaps a third of the bromine taken, was used in the 

 work ; and this was redistilled with the further rejection of the first 

 and last portions. The remainder was analyzed quantitively with pure 

 silver in order to test its freedom from chlorine, with very satisfactory 

 results. The silver was prepared, weighed, and dissolved with great 

 care, the precipitate was collected upon a Gooch crucible, and all 

 weighings were reduced to the vacuum standard. 



Purity of Hydkobromic Acid. 



No. of 

 Experiment. 



(3) 



(4) 



Weight of Silver. 



1.86058 

 1.72320 



Weight of 

 Argentic Bromide. 



3.23884 

 2.99983 



Percent of Silver in 

 Argentic Bromide. 



57.446 

 57.443 



Average 57.444 



Stas found 57.445 



Preparation of Zincic Bromide. For experiments 5 and 6 zincic 

 bromide was made by simply dissolving in a platinum dish the pure 

 oxide in the pure acid described above. For experiment 7 similar 

 zincic bromide was sublimed in a wide glass tube in a current of pure 

 dry carbon dioxide. The next experiment, No. 9, was made with 

 similar zincic bromide prepared wholly in glass and not sublimed. 

 A large portion of the substance was then prepared by exact neutrali- 

 zation and evaporation in a platinum dish, a strip of pure zinc was 

 added to precipitate a trace of platinum, — which had been dissolved 

 because of the presence of traces of oxidized nitrogen in the oxide, — 

 and the whole was subjected to crystallization. The mother liquor 

 served for analysis 8, and the pure white crystals for the third series 

 of preliminary determinations (Experiments 10, 11, 12, and 13). 



Preparation of Silver. — This substance was prepared by the method 

 described in a recent paper upon the atomic weight of barium.* 



Pure argentic chloride was reduced by means of pure sodic hydrate 

 and invert sugar, and the metal was washed and fused in a gas flame 



* These Proceedings, XXVm. 22; XXIX. 64. 



