[ 369 1 
bafe, by means of common air, during the evapora- 
tion of the water in which they are diffolved, as will 
be (hewn hereafter. 
The mephitic air of the acidulce , although it is 
foluble in water, and imparts thereto its brifk and 
pungent tafte, which has been ufually {filed fubacid ; 
and although it produces effects exadlly fimilar to thofe 
of acid fpirits (by readily uniting to various earthy fub- 
ftances, which of themfelves are not foluble in wa- 
ter, but, by their union with this aereal fluid, are 
rendered foluble therein, and communicate to the 
water peculiar favours, and form therein faline con- 
cretes of the neutral kind ; which concretes, fo 
formed, are again feparable into their component 
ingredients, by all thofe ways by which the acid and 
alcaline principles of other neutral falts are feparable 
from each other) yet it differs from all acid fpirits, 
found in a liquid form, in its rare texture and its 
elaftic quality, and in not ftriking a red colour with 
fyrup of violets, and other blue tindfures of vege- 
tables ; which change in the blue colour of thofe 
tindfures, is ufually effeemed a teft of the prefence 
of an acid. Befides the trials which other gentle- 
men and myfelf have made, by mixing fyrup of 
violets with pure water, impregnated with various 
kinds of mephitic air, in which no change in the 
colour of the fyrup was obferved, I have for feveral 
days fufpended pieces of linen, that had been dyed 
blue with frefh juice of violets, in the mephitic air 
of spa water, and alfo in that of chalk; and, when 
the linen was taken out of the faid air, did not 
perceive its blue colour in any wife changed, al- 
Vol. LX1V. B b b though 
