MUTUAL DliCOMPOSITIOA’. 
11 
almost Instantaneously, is soon transformed into a crimson Mutual <lc- 
pow tier, wliicli is composed of crystals, which are too small to 
be disiineuished as to their figure, even with a magnifier. The ble neutral 
11 1- 1 r • . , sails, &c. 
liquid becomes alkaline as in the preceding expenment, and 
likewise contains the sub carbonate of potash ■, the specific 
gravity of this red precipitate is much greater than that of the 
chromate of lead, it is completely insoluble, and does not 
effervesce with the nitric acid, but it immediately turns to a 
yellow colour, and yields the oxide of lead to this acid. I shall 
confine myself in the present instance to observe, that it is a 
sub-chromate similar in its proportions to the sub-carbonates, 
that is to say, in which the chromic acid is combined with a 
quantity of the oxide of lead exactly double that which is 
found ill the neutral chromate. 
I shall return in a particular memoir to this salt, and several 
others of which I have had an opportunity of verifying the 
existence : these details at present would lead me too far from 
my subject. 
The result of all the preceding facts is — 1 st. that all the in- Result of tlw 
soluble salts are decomposed by the subcarbonates of potash 
and of soda, but that a mutual exchange of the principles of 
these salts cannot, in any case, be completely made ; or, in 
otlier words, that the decomposition of the sub-carbonates is 
only partial ; 2 d. that all the soluble salts, of which the acid 
forms, with the base of the insoluble carbonates, an insoluble 
salt, are decomposed by these carbonates, until the decompo- 
sition has reached a cert.aiu limit which it cannot pass. 
\Ve sliall now endeavour to trace the origin of these pheno- 
mena in appearancee so contradictory.* 
On a first examination it is evident these decompositions dif- 
fer essentially from all those that have been hitherto observed. 
If it has already been remarked, that the reciprocal action of 
two salts may give rise to opposite results, the cause has been 
found to consist in a difference of the circumstances necessary 
to obtain such or such a result. The different degrees of tem- 
perature 
