C 223 ] 



Consequently per Bergman 100 grs. common magnefia fhould 

 lofe 55 per cent, in a ftrong heat, and per Butini it fhould lofe 

 nearly 60, and with this determination two experiments of Klap- 

 roth's agree. See 2 Klapr. 9 and 20 ; yet in another experiment 

 the lofs was but ■r%%, 2 Klap. 1 74. 



Hence we fee the proportions of air and water are variable, but 

 the fum of both generally amounts to 55 per cent, at theleaft, and 

 and hence I rate the mere earthy part in common magnefia at 45 

 per cent, when by a ftrong heat lefs is found I believe the differ- 

 ence to have been volatilized. The various proportions of fixed 

 air arife from the various proportions of it contained in the dif- 

 ferent precipitants ufed in obtaining magnefia. 



Note however, the water may gradually be expelled from 

 common magnefia in a heat much below ignition. 



Epsom. 



In my former paper I have ftated that 35 grains of common 

 magnefia, containing 15,7^ of mere earth, were faturated by 50 

 grains of vitriolic acid, whofe fp. grav. was 1,5654, diluted with a 

 large proportion of water, but containing, as appears by the table, 

 27,23 real acid, and from this and a comparative experiment, I de- 

 duced that 100 parts of cryftallized Epfom contained 17 of mere 



earthj 



