10 
MUTUAL UECOMPOSITIOS. 
fle- 
ronipofition 
of il «■ insolu- 
L*o ni-rirdl 
salts, &*;. 
^Vlien, ■ therefore, the first portions of tlie sulphuric acid have 
been preci|)itated from the sulphate of soda or po;a’'li, the 11- 
c}uor, becoming by that means charged with excess of alkali, 
dissolves a part of the sulphate <jf lead ; and if it contained 
carbonic acid, this sulphate would be immediately transformed 
into a carbonate that would be preeipiialed. At tins period, 
therefore, the decomposition can make no further progress. 
For tlie same reason, the lesults of the inverse experiments 
ditTcr from tinrse wlii-ii are presented by all tlie other salts. 
1’Lere is no limit in the aciion of the sub-carbo-ate of potash, 
or of soda, on tlie sulphate of lead j but tlie decomposition 
continues till there is evidently no longer any carbonic acid in 
the liquid 
Tlie explanation of the two preceding anomalies is still fur- 
ther cunfnined by the decomposition of these two carbonates 
by the sulphates of magnesia and ammonia, of which the 
bases form, w iib c.aibonic acid, an insoluble or volatile salt, 
which, by separating itself from the liquid, in proportion as it 
is formed, continues to restore the primitive circumstauces. 
I have analysed several salts that have been thus regenerated, 
irem their base of barytes, stromian, and of lime, and their 
proportions did not appear to me to difl'er from those which 
they had when they were obtained by direct precipitation j 
but il is not so with some of the metallic salts. 
If a perlectly neutral solution of the chromate of potash be 
poured upon an excess of carbonate of lead well pulverised, 
these two salts are mutually decomposed even at the ordinary 
temperature of from 10^tol.'3“. In this case, the carbonic 
ficid is not disengaged, the liquid turns a pale yellow, and be- 
comes very^ alkaline, and the precipitate at the .same time 
takes a yellow colour, and contains chromate of lead. The 
equilibrium is, without delay, established, and the carbonate 
of lead does not expeiience any further alteration, although 
there is still some chromate of potash in solution. 
Bui if the experiment be performed at the temperature of 
cbuiliiron, and on the contrary an^ excess of the chromate of 
potash be employed, the chromate of lead which is formed 
almost 
