16 
MUTUAL DECOMPOSITION. 
Mutual de- 
composition 
ot tlie inso u 
ble ne.nfi ai 
salts, &c. 
successive additions of alkali, the liquid can never be deprived 
of the whole of the carbonic acid it contains. 
If these results be compared with experiments C and E, it 
will be seen, that the solution which can no longer act upon the 
insoluble salt, (exp. C) is more alkaline than that which has 
no longer any action upon the insoluble carbonate (exp. E.) 
This difference may be measured by the proportion of the 
quantities of carbonic acid and sulphuric acid, which are then 
found in the two fluids. When the carbonate of potash can 
no longer decompose the sulphate of barytes, the carbonic acid, 
which remains in the solution, is to the sulphuric acid nearly as 
: : 3 : 1, and wlien the sulphate of potash can no longer act 
upon the carbonate of barytes, these two acids are nearly in the 
same relation as 3 to 2 ; from whence it follows, that the first 
liquor is much more alkaline than the second. 
It is easy to account for this difference, by examining the 
conditions of the equilibrium established in the two cases. 
When the sulphate of potash no longer decomposes the car- 
bonate of barytes, it is because the excess of alkali, which is 
developed in the liquid, can form an equilibrium against the 
power with which the sulphate of barytes tends to form itself 
under these circumstances. When the sub-carbonate of pot- 
ash can no longer decompose the sulphate of barytes, it is in 
consequence of the excess of alkali in the liquid not being 
sufficiently considerable to overcome the cohesion peculiar to 
this salt. Now, we know that, in order to overcome the effect 
of the cohesion of a body, when this effect is accomplished, it / 
requires a greater force than that w'hich will be precisely neces- 
sary to oppose the accomplishment of the same effect. There- 
fore, tlie sub-carbonate of potash ought to cease to decompose 
the sulphate of barytes, before the sulphuric and carbonic acids 
are in that relation in which these two acids are found when 
the equilibrium is established by the inverse experiment. 
Hence we may deduce this inference, that a mixture of sul- 
phate of potash, and of sub-carbonate of potash, in which the 
proportions of the sulphuric acid and carbonic acids shall be 
between the two limits which I have pointed out, will have r>o 
' action 
