MUTUAL DECOMPOSITION. 
15 
The insoluble carbonates have, as is known, a composition :uauial «K*- 
analogous lo that of the soluble sub-carbonates ; aiul though 
the force of the cohesion they possess, diminishes the energy of l»Ie luniial 
the alkali they contain in excess, it does net entirely destroy it. ’ 
When an insoluble carbonate is in contact with a neutral sch.ble 
salt, the base of the carbonate must tend to take pait of the 
acid of the neutral salt ; and if, from this uiiitn, an in»t.iuble 
salt can result, the'force of cohesion peculiar to this compound, 
will determine the formation. The carbonic acid, i f which 
the elasticity is no longer overcome bv the affinity of the base, 
combined wiili a tnore fixed acid, escapes in tlie lorm of gas — 
the same elVect being prodncerl on liesii quantities, the liquid 
becomes sufficiently alkaline to absorb the carbonic acid in its 
nascent state j and then the sub r aibonate of potash or of 
soda is formed, which replaces the dtcomposcd neutial salt. 
The precipitation of tlie acid on the insoluble carbonate, and 
the absorpiioti of the carbonic acid by the liquid, continues 
until the resistance which the excess of alkali so dcvelojied 
opposes tire precipitation of the acid, and forms an equili- 
brium to the force by which that precipitation was effected. 
All actloti then ceases, so that the more cohesion the insoluble 
salt possesses, the greater will be the proportion of acid taken 
from the soluble s.ilt. 
By admitting this explanation, all the phenomena which be- 
long to these decompositions, are pctfectly accounted for. We 
see, first, why all the insoluble salts, without exception, are 
decomposed by the sub-carbonates of jjotash and soda, because 
there is not one of these salts which cannot be decomposed 
partially by potash or soda ; secondly, that the .-.ub-carbonates 
which I have named are the only ones that can possess this 
general property, because the c.nbonic is the only acid which 
can form insoluble contpounds w ith the bases of all the inso- 
luble salts without neutralizing them. Thirdly, w hy the addi- 
tion of potash or caustic soda makes the decomposiiion make 
fresh progress; for, in this case, by the increase of the mass 
of alkali, a fresh quantity of insoluble carbonate should be 
formed. But from the expciiment (^F) it is seen, dial by the 
sue- 
