What Heat Is Not

It is tremendously instructive to talk about the following four features exemplifying what heat is not:

• Heat is not a fluid that passes from hot bodies to cold bodies, as was supposed during the 18th century. In the “caloric” hypothesis postulated at that time, heat was thought to be a fluid, termed as “caloric”, and efforts were made to isolate it and weigh it. The temperature increase which takes place during metal-turning was described to be the escape of the caloric as the material became sub-partitioned. The caloric theory was lastly disproved by count Rumford in the year 1798 by means of his well-known cannon-boring experiment.

• Heat transfer to a system does not forever cause a temperature increase. For illustration, throughout phase changes like melting and boiling, there is no temperature change accompany the heat transfer.

• It is not only heat transfer that can cause a temperature increase. Work done on a system, since for illustration, stirring of the fluid in an insulated vessel, outcome in a temperature increase.

• Heat is not a property of system.