34 On the Metallic Salts. 
otherwise one substance would become alternately the solvent 
and precipitant of the salt. 
From the tenor of our papers it cannot be misconceived thas 
water was intended as the medium of solution, particularly as I 
stated the acid as the agent promoting the solubility, not as dis- 
solving the salt; and those least acquainted with chemistry are 
fully satisfied that neither the salts, alkalies, nor even acids them- 
selves are soluble without such medium. 
H. evidently finds a difficulty in the attempt to reconcile 
the incongruity of one body assisting alternately the solution and 
precipitation of a salt. With him I should find some hesitation 
in admitting the fact, unless it could be accounted for on ra- 
tional principles: but we observe ammonia precipitating and 
redissolying the metallic salts; we observe likewise. water sa- 
turated with a salt beginning to crystallize,—the crystallization 
proceeding to a certain point, and the water then redissolving 
the crystals deposited. It is needless here to enter into the 
causes producing such effects, I merely wished to show that che- 
mistry was not without facts of this kind. With respect to the 
case under consideration, acid cannot be added to an unlimited 
extent ; for upon the addition of too considerable a quantity the 
salt may be deprived entirely of the water by superior affinity, 
as Berthollet has clearly demonstrated, 
The slight degree of acid, either in excess or free, which is 
apparent by the test, unless supported by other very powerful 
proofs cannot be depended on as decisive: the test proving no 
more than that +,4,;dth or ,,!,,dth part of the solution was acid, 
which minute portion might possibly adhere to the crystals. 
If a sufficient quantity of acid existed in the salts to require 
the preposition super, an effervescence on the affusion of water 
and the addition of carbonated alkali, would be observed in- 
variably; but which is seldom the case with the neutral salts 
carefully procured. Besides, many crystallized salts, on the ad- 
dition of water, divide into super- and sub-salts; the former solu- 
ble, the latter insoluble or nearly so: and sometimes the at- 
traction of the water for the acid is sufficiently strong in a de- 
gree to overcome the attraction of the acid for the base; either 
of which might be given as a reason for the indication of 
acidity. 
The salts of lead are conspicuous as being generally insoluble, 
owing probably to the great attraction between the acid and 
hase; and it has not been denied them, on that account, to 
class with the neutrals, and they are soluble on the addition of 
free acid. Not only an increase of the acid forming the salt, 
but often the addition of a different acid, as the acetic acid to 
the 
