iyS ESSAYS AND OBSERVATlOlSfS 



grains. This calcined magnejia was diffolved 

 in a fufficient quantity of Tpirit of vitriol, and 

 then again feparated from the acid by the ad- 

 dition of an alkali, of which a large quanti- 

 ty is neceflary for this purpofe. The mag- 

 mfia being very well walhed and dryedj 

 Weighed one dram and fifty grains. Iteffef* 

 vefced violently, or emitted a large quantity 

 of air, when thrown into acids, formed a red 

 powder when mixed with a folution of fub- 

 limate, feparated the calcarious earths from 

 an acid, and fweetened lime-water : and had 

 thus recovered all thofe properties which it 

 had but jufl now loft by calcination : not 

 had it only recovered its original properties, 

 but acquired befides an addition of weight 

 nearly equal to what had been loft in the firej 

 and, as it is found to effervefce with acids, 

 part of the addition muft certainly be air. 



This air feems to have been furniflied by 

 the alkali from which it was feparated by 

 the acid ; for Dr. Bales has clearly proved, 

 that alkaline falts contain a large quantity of 

 fixed air, which they emit in great abundance 

 when joined to a pure acid. In the prefent 

 cafe, the alkali is really joined to an acid,, but 

 without any vifible emiflion of air \ and yet 



the 



