“PHYSIGAL anv LITERARY. 193 
and twelve grains. This calcined magne- 
fia was diffolved in a fufficient quantity of 
- fpirit of vitriol, and thea again feparated 
from the acid by the addition of an alkali, 
of which a large quantity is neceflary for 
this purpofe. The magnefia being very 
well wafhed and dried, weighed one dram 
and fifty grains. Ir effervefced violently, 
or emitted a large quantity of air, when 
thrown into acids; formed a red powder 
when mixed with a folution of fublimate ; 
feparated the calcarious earths from an 
acid, and fweetened lime water: And had 
thus recovered all thofe properties which 
it had but juft now loft by calcination: 
Nor had it only recovered its original pro= 
perties, but acquired befides an addition 
of weight nearly equal to what had -been 
loftin the fire; and, as it is found to effer- 
yefce with acids, part of the addition 
muft certainly be air. 
Tuts air feems to have been furnifhed by 
the. alkali from which it was feparated by 
the acid; for Dr Hales has clearly proved, 
- that alkaline falts contain a large quantity 
of. fixed air, which they emit in great a= 
mv eL. II. Bb bundance 
