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double the pressure of isolated steam requires some 460° of 
sensible heat. 
If we look to the 140° of latent heat in water over that 
in ice, it will be seen that in lieu of being expended by the 
heat thus absorbed in melting the ice, the water is contracted 
in bulk ; for at temperatures from 32° to 40° ice floats with 
about one sixth of its bulk above the surface. The notion, 
therefore, that heat ceases to be sensible by reason of the 
expansion of bodies when it becomes latent in them is clearly 
shown to be a fallacy. 
I come now to notice the latent heat that becomes sensible 
by the union of a solid with a gas. The latent heat in oxy- 
gen and carbon being in excess of that in carbonic acid, by 
the formation of this acid in breathing, the supply of sensible 
heat is duly maintained to keep up the temperature of 
warm-blooded animals, and the excess of heat evolved in 
the lungs is carried off by converting water into steam, 
which passes out with the breath. If the whole heat so 
evolved were to remain sensible, it would destroy the living 
functions. 
Many other mutations of heat depending on the vital 
energies were explained in a former paper, and may be 
here passed by, with the remark that this entire class of 
changes, as in the case of respiration, are effected by 
chemical forces called into action by vital organisms. 
The alternate changes of sensible and latent heat de- 
pending on the constituent forms of bodies, and upon 
the chemical forces so called into action, might be shown 
in a hundred other cases, but the above will suffice 
to mark the principle on which the mutations of heat 
depend. Apart then from the chemical relations of heat 
