464 On the two great powers, (Sept. 
the known law, that in a change from a dense to a rarer state, heat is 
not evolved, but on the contrary becomes latent. Though this is al- 
most an invariable law, in a simple change of any solid A, into a gas 
A; yet if in becoming gaseous, A undergoes a change into another 
gas, B, an absorption of heat is not a necessary consequence; for the 
heat in the solid A may be sufficient to keep B in the state of gas, 
or may even be more than requisite, in which case some heat will be 
evolved. 
Thus the oxvgen, in the nitre of the gunpowder, during the explo- 
sion combines with the carbon and sulphur. The carbonic and 
sulphureous acid gases may not require so much heat for their existence 
in the gaseous state, as is afforded by the solid oxygen; hence heat 
will be evolved. If the experiments of Lavoisinr and CRawrurD may 
be admitted as at all correct, they will prove the justness of this ex- 
planation. 
Lavoisier inferred from his experiments, on the combinations of 
oxygen gas, that in nitre it retains Z of the heat, on which its gaseous 
state had depended. Crawrurp has stated the capacity of oxygen gas, 
as much greater than that of any of its compounds, and hence Z of its 
heat will be more than sufficient to supply the latent heat of the 
carbonic and sulphureous acid gases, formed in this instance. 
_ The late experiments of MM. Ciement and Drsormas, if correct, 
would show that the capacity of carbonic acid gas is equal or superior 
to that of oxygen, and would increase the difficulty of the explanation 
by making the one offered inadmissible. It must however be consi- 
dered, that no conclusion can be drawn with regard to the habitudes of 
caloric from instances of sudden and violent chemical and mechanical 
action. Thus no small part of the heat may be liberated by the 
resistance offered by the air to the sudden expansion of the gases 
formed. Whence much heat that would have been latent became 
caloric of temperature at the moment of the explosion, and whatever 
was extricated would be readily absorbed again from the air on the 
diffusion of the gaseous products of the powder. 
Again, in so great a chemical change we cannot from any established 
law affirm, a priori, that heat should be either liberated or absorbed. 
Admitting the capacity for heat of the gaseous products to equal, or 
even exceed, that of the gases condensed in the nitre of the powder, 
it does not all follow that the datent heat due to the gaseous state 
of the former should equal that of the latter gases; and these appear in 
nitre to retain this heat, though solidified by the intensity of the 
affinities. 
[To de continued.]} 
