242 ESSAYS anp OBSERVATIONS | 
the phial very frequently. After fome days 
the powder was increafed to more than 
double its former bulk; and, when the 
phial was opened, the alkaline {pirit emit- 
ted a moft intolerably pungent fmell. It 
likewife floated upon water, but was not 
perfectly cauftic; for it ftill yielded fome 
air when mixed with acids, and alfo ren- 
dered lime-water turbid : Neither of which 
would probably have happened if I had 
ufed a greater quantity of maguefia, or 
had allowed the mixture to remain a lon- 
ger time inthe phial. I now wafhed out 
the whole of the mixture into a bowl, and 
dryed the maguefia until it loft all fmell 
of the alkali. It weighed a dram and fif- 
ty eight grains, effervefced violently with 
acids, and therefore contained a large 
quantity of air, which had been drawn 
from the alkali by a ftronger attraction. 
HaviNc formerly fhewn, that mague- 
fia faturated with air feparates an acid 
from a calcarious earth, which it is not 
able to do after being deprived of its air 
by fire; I now fufpected that the air was 
the caufe of this feparation, becaufe I 
found 
