^48 M. Berzelius 071 some Compounds 
what is contained by the magnesia. We have still to consider, 
in what they are united. Those who have paid no attention to 
the manifold relations which subsist between the oxygen of 
bases, and that of the acids combined with those bases, (rela- 
tions which constantly appear, except when the oxygen con- 
tained by the acid in its lowest degree of oxidation is to that 
contained at its highest, as three to two*), will probably say, 
that magnesia alba is a subcarbonate, composed of 2 atoms of 
acid, combined with 3 atoms of base, and 3 of water. But let 
us examine these ratios of combination, before we acknowledge 
their accuracy. It is plain, that if in reality they constitute 
a salt having an excess of base, the carbonic acid must possess 
the property of forming other salts having an excess of base, and 
saturated with their bases in a similar degree. 
It is well known that the green carbonate of copper is a sub- 
carbonate, in which the carbonic acid is combined with twice as 
much oxide of copper as in the ordinary carbonate, which re- 
sults from decomposing the neutral sulphate of copper by an 
alkaline carbonate. But in the mineral kingdom there is ano- 
ther carbonate of copper, — the blue one, wliich I have attempt- 
ed to prove, from the analyses of Klaproth and Vauquelin, to be 
a carbonate of copper, combined with a hydrate of the same 
metal = Cu Aq^ -f 2 Cu +. (Afharidlingar Fysik, &c. iv. 
130). This species of the carbonate of copper has since been 
analysed by Mr Philips; and the result of his investigation 
agrees, even in the decimal parts, with that calculated from the 
formula which I have just given. On the other hand, if this 
substance is not a kind of double salt, composed of the hydrate 
and the neutral carbonate of copper, (as its colour also seems 
to indicate), it must be a subcarbonate. But this subcarbonate 
could neither be analogous to that which may be supposed to 
form magnesia alba, nor conformable to the laws of chemical 
proportion, since it would be composed of 3 atoms of base, with 
4 atoms of acid. I may observe farther, that the water com- 
bined with salts, commonly called their water of crystallisation, 
* Which happens in the acids having nitrogen or phosphorus for their base. 
*}• Cu signifies oxidum cupricum» The rest of the symbols have already been 
explained. 
