280 SALTS 



No other genus of salts, except those of soda, 

 contains 12 atoms of water. 



4. SALTS OF BARYTES. 



Sulphate, 1. Sulphate of barytes. This well known 

 salt contains no water of crystallization ; though 

 the native crystals decrepitate, and probably, 

 therefore, contain a little water mechanically 

 lodged between their plates. I find that preci- 

 pitated sulphate of barytes, if it be well washed, 

 and thoroughly dried by exposure to the air for 

 a sufficient time, retains about 3 per cent, of 

 water, which is easily driven off by exposing the 

 powder to a red heat in a platinum crucible. 

 This amounts to rather more than the third of 

 an atom of water which is only mechanically 

 lodged in the pores of the powder, and not 

 chemically combined with it. The constituents 

 of the salt are 



1 atom sulphuric acid 5 

 1 atom barytes 9*75 



14-75 



Nitrate, 2. Nitrate of barytes. This salt usually crys- 

 tallizes in octahedrons ; it is not altered by ex- 

 posure to the air ; it is apt to be contaminated 

 with muriate of barytes, and then contains 



