insoluble; by afterwards evaporating the water, we
obtain the potash in a white concrete form: It is very fixed even in a
very high degree of heat. I do not mean here to describe the art of
preparing potash, or the method of procuring it in a state of purity,
but have entered upon the above detail that I might not use any word not
previously explained.

The potash obtained by this process is always less or more saturated
with carbonic acid, which is easily accounted for: As the potash does
not form, or at least is not set free, but in proportion as the
charcoal of the vegetable is converted into carbonic acid by the
addition of oxygen, either from the air or the water, it follows, that
each particle of potash, at the instant of its formation, or at least of
its liberation, is in contact with a particle of carbonic acid, and, as
there is a considerable affinity between these two substances, they
naturally combine together. Although the carbonic acid has less affinity
with potash than any other acid, yet it is difficult to separate the
last portions from it. The most usual method of accomplishing this is to
dissolve the potash in water; to this solution add two or three times
its weight of quick-lime, then filtrate the liquor and evaporate it in
close vessels; the saline substance left by the evaporation is potash
almost entirely deprived of carbonic acid. In this state it is soluble
in an equal weight of water, and even attracts the moisture of the air
with great avidity; by this property it furnishes us with an excellent
means of rendering air or gas dry by exposing them to its action. In
this state it is soluble in alkohol, though not when combined with
carbonic acid; and Mr Berthollet employs this property as a method of
procuring potash in the state of perfect purity.

All vegetables yield less or more of potash in consequence of
combustion, but it is furnished in various degrees of purity by
different vegetables; usually, indeed, from all of them it is mixed
with different salts from which it is easily separable. We can hardly
entertain a doubt that the ashes, or earth which is left by vegetables
in combustion, pre-existed in them before they were burnt, forming what
may be called the skeleton, or osseous part of the vegetable. But it is
quite otherwise with potash; this substance has never yet been procured
from vegetables but by means of processes or intermedia capable of
furnishing oxygen and azote, such as comb