ents, which
seem to shew a greater difference between the forces wherewith the
calcarious earth and magnesia attract fixed air, than between those
which dispose them to unite with the acid. The repulsions however hinted
in the second are perhaps more doubtful, tho' they are suggested in many
other instances of decomposition; but the bounds of my present purpose
will not allow me to enter upon this subject, which is one of the most
extensive in chemistry.

We meet also with a difficulty with respect to the volatile alkali
similar to the above. Thus a calcarious earth that is pure or free of
air has a much stronger attraction for acids than a pure volatile
alkali, as is evident when we mix quick-lime with salt ammoniac; for the
alkali is then immediately detached from the acid: and agreeably to this
I found, upon trial, that a pure or caustic volatile alkali does not
separate a calcarious earth from an acid. Yet, if we mix a mild volatile
alkali, which is a compound of alkali and air, with a compound of acid
and calcarious earth, these two last, which attract one another most
strongly, do not remain united; but the acid is joined to the alkali and
the earth to the air, as happens in the precipitation of a calcarious
earth from an acid, by means of the common or mild volatile alkali.

I remember likewise a parallel instance with regard to quick-silver.
This metal has an attraction for the vitriolic acid, and when joined to
it appears under the form of turbith mineral: but this attraction is
weaker than that of the fixed alkali for the same acid; for if we mix a
dissolved salt of tartar with turbith mineral, the turbith is converted
into a brown powder, and the alkali into vitriolated tartar; which
change happens the sooner, if the pure or caustic alkali is used. Yet,
if to a compound of quick-silver and the nitrous acid, we add a compound
of the fixed alkali and the vitriolic acid, or a vitriolated tartar, and
digest the mixture with a strong heat, the vitriolic acid does not
remain with the alkali, but is joined to the quick-silver which it
attracts more weakly, composing with it a turbith mineral; while the
alkali is joined to the nitrous acid which it likeways attracts more
weakly than it does the vitriolic, and is converted into salt-petre.

From some of the above experiments, it appears, that a few alterations
may be made in the column of acids in Mr. _Geoffroy's_ table of elective
attractions, and that a new column