OF MAGNESIA. 303 



reign matter amounts only to 2tbth of the min- 

 eral. 



5. Magnesia alba of the shops. It is obvious, Magnesia 

 from the analysis of this powder by different 3 

 chemists, that its composition varies considera- 

 bly. Berzelius has shown that the composition 

 is regulated by the quantity of water employed, 

 and by the temperature : for the powder is ob- 

 tained by precipitating the sulphate and muriate 

 of magnesia by an alkaline carbonate. Berze- 

 lius analyzed a portion of it washed in boiling 

 water, till the liquid ceased to dissolve any more. 

 He found it a compound of 



Magnesia 44-58 or 3-434 



Carbonic acid 35'70 - 2-75 

 Water 19-72 - 1-519 



100-00 



This approaches 



I atom carbonic acid 2-75 

 1J atom magnesia 3-75 



II atom water 1-6875 



But Berzelius considers it as a compound of 3 

 atoms carbonate of magnesia and of 1 atom of 

 quadrohydrate 



3 atoms carbonate of magnesia 1 5'75 

 1 atom quadrohydrate 7 





22-75 * 

 * Afhandlingar, VI. 24. 



