is a constituent element of all the alkalies, as is the case with
ammoniac; but we have only slight presumptions, unconfirmed by any
decisive experiments, respecting the composition of potash and soda.
3. _Of Ammoniac._
We have, however, very accurate knowledge of the composition of
ammoniac, or volatile alkali, as it is called by the old chemists. Mr
Berthollet, in the Memoirs of the Academy for 1784, p. 316. has proved
by analysis, that 1000 parts of this substance consist of about 807
parts of azote combined with 193 parts of hydrogen.
Ammoniac is chiefly procurable from animal substances by distillation,
during which process the azote and hydrogen necessary to its formation
unite in proper proportions; it is not, however, procured pure by this
process, being mixed with oil and water, and mostly saturated with
carbonic acid. To separate these substances it is first combined with an
acid, the muriatic for instance, and then disengaged from that
combination by the addition of lime or potash. When ammoniac is thus
produced in its greatest degree of purity it can only exist under the
gasseous form, at least in the usual temperature of the atmosphere, it
has an excessively penetrating smell, is absorbed in large quantities by
water, especially if cold and assisted by compression. Water thus
saturated with ammoniac has usually been termed volatile alkaline fluor;
we shall call it either simply ammoniac, or liquid ammoniac, and
ammoniacal gas when it exists in the aeriform state.
4. _Of Lime, Magnesia, Barytes, and Argill._
The composition of these four earths is totally unknown, and, until by
new discoveries their constituent elements are ascertained, we are
certainly authorised to consider them as simple bodies. Art has no share
in the production of these earths, as they are all procured ready
formed from nature; but, as they have all, especially the three first,
great tendency to combination, they are never found pure. Lime is
usually saturated with carbonic acid in the state of chalk, calcarious
spars, most of the marbles, &c.; sometimes with sulphuric acid, as in
gypsum and plaster stones; at other times with fluoric acid forming
115