RICHARDS AND ROGERS. — ATOMIC WEIGHT OF ZINC. 



163 



increases about 0.001 of its apparent volume for each degree of tem- 

 perature ; and the small appropriate correction is applied below. 



Specific Gravity of Zincic Bromide. 



The value 4.22 is used in the work which follows. In this connec- 

 tion it may be of interest to compare the sj^ecific gravities of the sub- 

 stances recently determined here. 



Specific Gravities compared with Water at 4°. 



PRELmiNARY ANALYSES OP ZiNCIC BrOMIDE. 



Preparation of Zincic Oxide. The zincic bromide used for the 

 first series of experiments was made by the action of pure hydrobromic 

 acid upon pure zincic oxide. For the preparation of the oxide "pure" 

 zinc of commerce was dissolved in pure dilute sulphuric acid, and the 

 solution was allowed to remain over an excess of the metal for several 

 weeks. The filtered solution was acidified with sulphuric acid, warmed, 

 and treated with well washed hydric sulphide, until a considerable 

 mass of pure white precipitate had formed. 



