MAGNESIA AND MAGNESIUM. 279 



SECT. VII. 



OF THE ATOMIC WEIGHTS OF MAGNESIA AND 

 MAGNESIUM. 



THE atomic weight of magnesia may be deter- 

 mined in the same way as that of the fixed alka- 

 lies. For sulphate of magnesia, which crystallizes 

 in four-sided prisms with square bases, and is per- 

 fectly neutral, may be rendered anhydrous by 

 heat, without losing any of its acid. 



1. 7*5 grains of anhydrous sulphate of mag- Atom of 

 nesia, and 13*%5 grains of chloride of barium, 

 were dissolved in two separate portions of dis- 

 tilled water. The two solutions being mixed 

 together and agitated, a double decomposition 

 took place, sulphate of barytes precipitated, 

 while muriate of magnesia remained in solution. 

 The supernatant liquid, after the sulphate of 

 barytes had subsided, was perfectly neutral. 

 Being tested by sulphate of soda, and muriate of 

 barytes, it did not become in the least muddy by 

 the addition of either of these reagents, showing 

 that it contained neither barytes nor sulphuric 

 acid. Hence, the sulphuric acid in 7*5 grains 

 of anhydrous sulphate of magnesia just saturates 

 the barytes from 13*25 grains of chloride of ba- 

 rium so that it amounts to precisely 5 grains. 

 The remainder of the salt consisting of magne- 



S 4 



