Caloric

Caloric, the name given by the old philosophers to the subtle, imponderable fluid that heat was supposed by them to be. The caloric theory that heat is a substance held its ground until this century. It stated that a hot body was one in which a temporary union of the substance of the body with caloric had taken place, and that the more caloric in the body the hotter it became. To explain the fact that rubbing makes a body warm, it was supposed that such rubbing had the effect of squeezing out the caloric as water from a sponge; but Count Rumford showed that there was no limit to the amount of heat that could be obtained by rubbing two pieces of metal together, an effect evidently in opposition to the caloric theory. Also Davy pointed out that two pieces of ice when rubbed together could be readily made to melt, thus actually giving out heat and yet possessing more than at first. The conclusions arrived at by these and similar experiments both qualitative and quantitative are that the heat given to a stationary body is to be measured by the amount of energy expended on it, and that heat is only a change in the form of this energy, probably kinetic or moving energy of the molecules themselves. The term caloric is still occasionally used in a popular sense to represent heat.