COMPOSITION OF OXIDE OF ZINC. 55 



2. CARBONATE OF ZINC. 



Carbonic acid . 2 '75 

 Oxide of zinc . 5-25 



3. ARSENIATE OF ZINC. 



Arsenic acid . 7*75 

 Oxide of zinc . 5-25 



We shall verify this statement by a rigid analysis 

 of these three salts. 



1. SULPHATE OF ZINC. 



Sulphate of zinc, or white vitriol, is a well A ^ a iy sis f 



sulphate of 



known salt which crystallizes in beautifully tran- zinc - 

 sparent four-sided prisms, terminated by four- 

 sided pyramids ; or if the crystallization be rapid, 

 it assumes the form of long slender white 

 needles. However carefully prepared, it always 

 reddens vegetable blues. But it crystallizes also 

 with an excess of acid. In that case, the crys- 

 tals assume the form of large flat rhomboids, 

 which are not altered by exposure to the air, 

 and may be raised to the temperature of at least 

 500 without being deprived of their excess of 

 acid.* 



* I am doubtful whether this salt constitutes a truly distinct species. 

 I found its composition 



1^ atom acid 6-66 

 1 atom oxide 5-25 

 8 atoms water 9-00 



20-91 



or, it consists of one atom of the protohydrate of sulphuric acid, combined 

 with three integrant particles of the neutral salt. 



D4 



