secondary order of combination, being formed by the union of two _mixts_
with each other, and may therefore be termed _compounds_. Hence I shall
not arrange the alkalies[31] or earths in the class of salts, to which
I allot only such as are composed of an oxygenated substance united to
a base.
I have already enlarged sufficiently upon the formation of acids in the
preceding chapter, and shall not add any thing farther upon that
subject; but having as yet given no account of the salifiable bases
which are capable of uniting with them to form neutral salts, I mean, in
this chapter, to give an account of the nature and origin of each of
these bases. These are potash, soda, ammoniac, lime, magnesia, barytes,
argill[32], and all the metallic bodies.
1. _Of Potash._
We have already shown, that, when a vegetable substance is submitted to
the action of fire in distilling vessels, its component elements,
oxygen, hydrogen, and charcoal, which formed a threefold combination in
a state of equilibrium, unite, two and two, in obedience to affinities
which act conformable to the degree of heat employed. Thus, at the
first application of the fire, whenever the heat produced exceeds the
temperature of boiling water, part of the oxygen and hydrogen unite to
form water; soon after the rest of the hydrogen, and part of the
charcoal, combine into oil; and, lastly, when the fire is pushed to the
red heat, the oil and water, which had been formed in the early part of
the process, become again decomposed, the oxygen and charcoal unite to
form carbonic acid, a large quantity of hydrogen gas is set free, and
nothing but charcoal remains in the retort.
A great part of these phenomena occur during the combustion of
vegetables in the open air; but, in this case, the presence of the air
introduces three new substances, the oxygen and azote of the air and
caloric, of which two at least produce considerable changes in the
results of the operation. In proportion as the hydrogen of the
vegetable, or that which results from the decomposition of the water, is
forced out in the form of hydrogen gas by the progress of the fire, it
is set on fire immediately upon getting in contact with the air, water
is again formed, and the greater part of the caloric of the two gasses
112