Sainte-Claire Deville’s Theory of Dissociation. 205 
But this state of dissociation is altogether founded on gra- 
tuitous assumptions. The ground from which it springs is this : 
that as compound bodies when heated expand, the constituents 
must recede from each other as well as the compound particles. 
But this proposition has yet to be proved. I believe many facts 
favour an opposite conclusion: for instance, not to speak of the 
manner in which solids and fluids, when szmple bodies, expand, 
being somewhat similar to the same process in compounds, Gay- 
Lussac’s law with respect to the equal expansion of all gases and 
vapours for equal increments of heat, would surely show that 
the constituents of a compound do not recede from each other 
in expanding. Hydrogen, or any other simple gas, and vapour 
of ether, or other compound gas, expand exactly according to 
the same law. Could this occur with the simple particles of 
hydrogen to the same extent precisely as with compound mole- 
cules of ether, where, instead of two, we have ten elementary 
atoms to divide the distance and moving force between them? 
The resistance to expansion of a gas by heat seems to be the 
weight of the atmosphere; and consequently in all gases, the 
same resistance being present, the same expansion is attained by 
a certain increase of temperature. Now in a simple gas the 
weight is the only resistance ; whereas, if Deville’s theory is cor- 
rect, there is in compound gases not only the weight, but the 
affinity of the constituents to be partly overcome; and yet the 
same expansion is noticed for the same increase of temperature 
in both. But this would be impossible, except we imagine that 
the separation of these constituents does not absorb heat, which 
we know it does. 
It seems to me that this fact alone, of the similar and equal 
expansion of simple and compound gases by heat, shows that 
no motion takes place in one which does not occur in the other ; 
therefore that no expansion of the particles themselves, that is, 
that no separation of the simple constituents of the compound 
molecule is produced by raising its temperature, and con- 
sequently that this state of dissociation does not exist. 
A consideration of other portions of the paper would lead me 
too far for the present, but I may recur to it if you think the 
subject sufficiently teresting for your Magazine. 
Your obedient Servant, 
THOMAS Woops, M. D. 
heat of chemical combination, he seems to think it an objection (page 177) 
that the whole expansion which would bean equivalent to the contraction 
of the combining particles is not seen in the compound produced; but 
surely, as this volume would be the temperature evolved by the combina- 
tion, it cannot remain longer than a moment in the compound; it must 
be dispersed to surrounding bodies. 
