COMPOSITION OF OXIDE OF ZINC. Gl 



so much so, that it is not easy to dry this car- 

 bonate without sustaining at least a partial loss 

 of the water. But I have more than once suc- 

 ceeded in getting it with the exact atomic 

 proportions. The carbonate of zinc occurs in 

 the mineral kingdom, sometimes anhydrous, and 

 sometimes containing 1 atom of water. 



3. ARSENIATE OF ZINC. 



This salt was obtained by the following pro- ofarsemate 

 cess: 18-12,5 grains of the crystallized sulphate of zmc * 

 of zinc, and 20*75 grains of arseniate of 

 soda were dissolved in separate portions of 

 distilled water, and the two solutions, after being 

 well mixed, were evaporated to dryness, and 

 the dry mass digested in distilled water. A dou- 

 ble decomposition took place, and arseniate of 

 zinc separated in the state of a gelatinous looking 

 matter. Being washed and dried in the open 

 air, it constituted a white powder, weighing 26-5 

 grains. But when heated to redness, the weight 

 was reduced to 13 grains. By a careful analysis 

 of this salt, I found that its constituents were 



1 atom arsenic acid 7*75 



1 atom oxide of zinc 5-25 



8 atoms water 9'0 



It would be easy to increase the number of 

 these examples j but those given are sufficient 



I 



