r oe 
228 ESSAYS anp OBSERVATIONS 
quently for two days, This, after being’ 
filtrated, formed a cream or cruft upon its 
furface when expofed to the air; changed 
the colour of the juice of violets into 
green ; feparated an orange coloured pow. 
der from a fclution of corrofive fubli- 
mate ; became turbid upon the addition 
of an alkali; was entirely {weetened by 
magnefia ; and appeared fo ftrong to the’ 
tafte, that I could not have diftinguifhed. 
it from ordinary lime-water. And when 
J threw fome falt ammoniac into’ the lime 
which remained, the vapour of the volatile’ 
alkali inmediately arofe from the mix- 
ture. 
In this experiment therefore the air is 
firft driven out of the chalk by an acid, 
and then, in order to feparate this acid 
from it, we add an alkali which has been: 
previoufly deprived of its air; by which 
means the chalk itfelf is alfo obtained 
free of air, and in an acrid form, or in the 
form of flaked lime. 
We have alfo feveral proceffes for ob- 
taining the volatile alkali in a cauftic 
form, which feem to be only fo many me- 
thods 
