MUTUAL DECOMPOSITION, 
17 
action either on the sulphate of bar)'tes, or on the carbonate of Mutnal de 
the same base, This is what experiment likewise confirms. of "the*hisol», 
I have already observed, that for the other insoluble salts l)le neutral 
there vvill be other relations of quantity; but there is always a ' * • 
certain interval, more or less considerable, between their limits. 
The sub-carbonates of potash and soda being likewise able 
to decompose all the insoluble salts in the dry way, and this de- 
composition depending on properties different from those upon 
which the decomposition is effected in the humid way, it was 
interesting to compare the results of these two different modes 
of decomposition. 
Experiment G . — I heated to ignition for an hour in a crucible 
of platina, a mixture of the sub-carbonate of soda, and sulphate 
of barytes in excess. The two salts entered into a state of 
fusion ; and after cooling, the mass was pulverized and placed 
in a filter, on which boiling water was poured. I expected to 
find the liquor neutralized, or not far distant from that state ; 
but, on the contrary, it was strongly alkaline, and effervesced 
briskly with the acids. On analysing it, I found that it con- 
tained carbonic and sulphuric acid in the same proportions as in 
a solution of the sulphate of soda exhausted upon the carbonate 
of barytes. This evidently arises from the sulphate of soda, 
in proportion as it dissolves, re-acting on the carbonate of 
barytes, with which it finds itself in contact, and this re- 
action is almost instantaneous. It is sufficient to pour a boiling 
solution of neutral sulphate of soda on the carbonate of barytes 
placed in a filtre, in order that more than three quarters of the 
sulphuric acid may be precipitated and replaced by a corres- ^ 
ponding quantity of carbonic acid. It is, therefore, impossible 
to verify by experiment whether, as the theory indicates, the 
exchange of the brse and the acid be completely made between 
the soluble sub-cnrbonates and insoluble salts, in operating by 
the dry way j but it is seen, that the decomposition proceeds 
much faUher than in the humid way. 
1 shall terminate this memoir with some observations on the 
measure of affinities, and on the applications that may be de- 
duced from the theory I have been explaining. 
Since the quaniity of sub-carbonate of potash and of soda 
Vol.XXXVI.—No. 166. C 
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