186 On Iodine. [Szpr, 
of chlorurets in solution in water, that when they are dissolved only 
a very slight change of temperature takes place ; while if the water 
were realiy decomposed, the variation would be very great. 
The temperature produced by the solution of a solid body being 
the result of two opposite causes, it is dificult to distinguish the 
heat owing to the combination of the liquid with the solid from 
that which is owing to the change of state in the solid. But inde- 
pendent of this consideration, I must remark, that some of the 
ehlorurets produce cold when dissolved in water, and others heat. 
Thus the chloruret of sodium sinks the temperature of the water 
about 3°5°, while that of calcium raises it more than 108°. Far- 
ther, if it be demonstrated that the forces, which determine the 
double saline decompositions, are sufficient to operate the separation 
of the elements of water and their union in the circumstances of 
which we are speaking, we ought to admit that the state of con- 
densation of the oxygen and hydrogen in water is little different 
from that which thev experience in the hydro-chlorate, and then the 
variations of temperature owing to the separation or re-union of 
these two elements ought to be but little sensible. Besides, my 
object is not to prove that only hydro-chlorates exist in solution in 
water. I believe, on the contrary, that according to the nature of 
the substance with which the chlorine is combined, the chlorurets 
may dissolve in water without undergoing decomposition, or be 
changed into hydro-chlorates during that solution. 
To acquire still further light on that head, I supposed that on 
mixing a solution of sulphate of ammonia with that of chloruret of 
calcium or barytes, there ought to be produced a great deal of heat, 
if these metals were not combined with oxygen; for having to pass 
into the state of oxide in order to combine with sulphuric acid, the 
decomposition of the water must necessarily take place, and its 
oxygen experiencing a great condensation on uniting to the calcium 
or barium, there ought to be a very sensible disengagement of heat. 
On mixing solutions of chloruret of calcium and sulphate of am- 
monia nearly in equal volumes, the temperature scarcely rose half a 
degree, though such a quantity of sulphate of lime was formed that 
the whole mixture became solid. The solution of chloruret of 
barium treated in the same way produced an elevation of about 3°5°. 
From these facts it would seem that in the solution of chloruret of 
calcium the metal is in the state of an oxide, while in that of chlo- 
ruret of barium the metal is still in the metallic state. 
Analogy, to which one should not vield too blindly in chemistry, 
but which ought not to be neglected when founded on a numerous 
series of phenomena, furnishes still, as we shall see, some proba- 
bilities in favour of the existence of the hydro-chlorates. 
It cannot be doubted that sulphur, and even phosphorus, ap- 
proach a good deal to chlorine and iodine, and that of course their 
combinations have an analogy with each other. But if we dissolve 
in water the sulphuret of potassium, we obtaima combination the 
odour of which announces the presence of bydro-sulphurie acid, 
