316 Affinity and Feat. 
A most remarkable experiment which M. Berthelot has 
made, by placing together carbonic oxide, water, and 
potash, belongs to actions of this kind. 
Carbonic oxide dissolves in potash, and absorbs during 
its extension in the liquid, a certain number of thermal 
units beyond that which the loss of wis viva by contrac- 
tion doubtless allows it to retain at the moment of its 
liquefaction. This solution, which takes place in very small 
quantity at a time, owing to the slight solubility of the gas, 
is really a considerable extension, which, thanks to disso- 
ciation by diffusion, gives to the molecules of carbonic 
oxide the heat necessary for entering into direct combina- 
tion with the elements of potash. In this reaction (it is, 
moreover effected with the slowness which characterises 
all operations where solution is necessary when the solu- 
bility is small) the heat is fixed which formic acid needs for 
its existence. It is the origin of this heat taken from the 
solution by a combination effected between bodies in the 
nascent state, and which will be disengaged in the form of 
sensible heat when formic acid is decomposed by spongy 
platinum, as has been done by Berthelot, or when formic 
acid is burned, as was done by Favre and Silbermann some 
time ago. 
Combination is almost always produced by the destruc- 
tion of motion, sometimes by the transformation of heat 
into motion. In the first case there is a disengagement of 
heat, in the second a cooling or absorption of heat. In 
the second category are to be included all those bodies 
which I have proposed to call explosive—that is, which 
render into insensible heat the motion they have acquired 
in absorbing latent heat. Formic acid, a great number of 
organic compounds, as well as the explosive compounds of 
nitrogen, are in the latter category; and these are rarely 
produced by the direct union of the elements but are ob- 
tained by the interchange of their elements in the body of 
more or less dilute solutions. It is assumed that then the 
molecules are in contact in the nascent state. Here we 
must be on our guard; this term still includes the idea of 
an occult cause. It must be employed with extreme re- 
serve and by it must be understood a system of circum- 
stances in which the molecules may change their state of 
equilibrium by finding about them latent heat or in 
general, the causes of motion necessary for producing and 
exciting this change of state. The origin of the expres- 
sion which renders this idea, implies an hypothesis which 
