Sainte-Claire Deville’s Theory of Dissociation. 203 
of state of the chlorine, how does it happen that the same amount 
is produced when the chlorine combines, not being in the gaseous 
state at all ? If hydrochloric acid and zinc are placed together, the 
chlorine unites with the zinc, and the same quantity of heat is 
evolved as when the zinc burns in the gas ; and the same amount is 
absorbed by the decomposition as if both the constituents again 
attained the gaseous state; or if (to take an instance where no 
gas is present, either in combination or decomposition) zine 
causes a deposition of copper from chloride of copper, exactly the 
same heat is produced by the combination of the chlorine and 
copper, and exactly the same quantity is absorbed by the decom- 
position, as if the chlorine and copper acted as gases, changing 
their state as they combined or decomposed. Unless, therefore, 
it is imagined that when the chlorine leaves the copper or hy- 
drogen it becomes for a time a gas and enters into the disso- 
ciated state, absorbing heat, and again becomes solid, giving it 
up, I cannot see how the temperature is raised. But even 
granting that it does so the phenomenon could not be accounted 
for, because when zinc decomposes chloride of hydrogen or 
chloride of copper, more heat is produced by the combination 
than is lost by the decomposition: and such could not occur if it 
were due to the latent heat of dissociation ; for the heat would be 
taken in the first instance from the materials afterwards heated, 
and so an exchange only, and not an increase, would be effected. 
It might be said that the zinc influences the result ; that is, that 
metals have a certain amount of heat connected with them which 
is given out in combining, and that this being greater in some 
instances than in others, might account for the increase of tem- 
perature when the zinc displaces the hydrogen. But if all bodies 
have definite quantities of heat, as Sainte-Claire Deville seems to 
think, the same order ought to be observed in the amounts evolved 
by their combination with the gases. For instance, if an equi- 
valent of chlorine, by uniting with zine, copper, silver, &c., pro- 
duces heat, the quantity of which varies in the order in which 
the metals are named, oxygen ought to do the same, if the 
heat evolved in combination was previously connected with the 
combining bodies: but it is known that such is not the case. 
Chlorine produces more heat with silver than it does with copper, 
and oxygen the reverse. Instances of this kind might, of course, 
be multiplied ; and they prove, I think, that no fixed amount of 
heat, resulting either from change of condition, or from latent 
heat becoming evolved as it does in the condensation of vapour, 
can be connected with matter as part of its constitution, inde- 
pendent of alteration of the relation of particles. 
Deville, in fine, thinks that every body possesses a certain 
amount of heat, or condition in itself whereby heat can be pro- 
