154 HISTORY OF CHEMISTRY [LKCT. ix.
(as base), both water atoms are driven off, and a hitherto
unknown salt, sodium metaphosphate, is produced. The
acid contained in this salt is characterised by being saturated
by one atom of base, whilst, in the free state, it contains
one atom of water. The silver compound was again different
from either of the others. In this case the ratio of the
quantities of oxygen in base and acid was as I to 5.
Finally, it was shown in the investigation that rneta-
and pyro-phosphoric acids, as well as the majority of their
salts, pass ,into ordinary phosphoric acid or a salt derived
from it, when boiled with water, or still better, when fused
with sodium carbonate.
Two important theoretical conclusions can be directly
deduced from Graham's investigation.
(i.) In acids there is a certain number of atoms of water,
and salts are formed by the replacement of these.
(2.) The atoms of the acids are not always equal in
number to the atoms of the bases, and in some, even the
ratio is variable. Thus Graham showed how, from the same
phosphoric anhydride, to prepare three hydrates which were
able to take up quite different quantities of base.
Liebig, in 1838, stated these conclusions with great clear-
ness and precision.8 A man of his genius could not, how-
ever, rest satisfied with publishing thoughts that were merely
conclusions drawn from the experiments of others. We are
indebted to Liebig for an excellent investigation of a series
of organic acids, from which it appeared that phosphoric acid
does not stand alone with respect to its behaviour towards
bases, but that in the cases of certain other acids, one atom
likewise possesses the property of saturating several atoms
of base. Founding, as he did, upon a broader basis, he
was then able to introduce the idea of the polybasic acids.
Liebig's experimental investigation embraces fulminic,
cyanic, meconic, comenic, tartaric, malic, citric, and other acids.
He finds relations amongst the salts of each of these acids,
8 Annalen. 26, 113 ; compare Coraptes Rewius. J, 863,