240 ESSAYS anp OBSERVATIONS 
feems to be confirmed by the following 
experiment. 
I expofed a fmall quantity of a pure 
vegetable fixed alkali to the air, in a broad 
and fhallow veiffel, for the fpace of two 
months; after which I found a number 
of folid cryftals, which refembled a neu- 
tral falt fo much as to retain their form 
pretty well in the air, and to produce a 
confiderable degree of cold when diffolved ° 
in water. Their tafte was much milder 
than that of ordinary falt of tartar; and 
yet they feemed to be compofed only of 
the alkali, and of a larger quantity of air 
than is ufually contained in that falt, and 
which had been attracted from the atmo- 
fphere: For they ftill joined very readily 
with any acid, but with a more violent 
effervefcence than ordinary; and they 
could not be mixed with the fmalleft por- 
tion of vinegar, or of the fedative falt, 
without emitting’a fenfible quantity of air, 
As it now appeared that feveral alka- 
line fubftances have an attraction for fix- 
ed air, I tricd a few experiments to learn 
the 
