Date of this Version
Until about 1750 the concepts of heat and temperature were not clearly distinguished. The two concepts were thought to be equivalent in the sense that bodies at equal temperatures were thought to "contain" equal amounts of heat. Joseph Black (1728-1799) was the first to make a clear distinction between heat and temperature. Black believed that heat was a form of matter, which subsequently came to be called caloric, and that the change in temperature of a body when caloric was added to it was associated with a property of the body which he called the capacity. Later investigators endowed caloric with additional properties. The caloric fluid was thought to embody a kind of universal repulsive force. When added to a body, the repulsive force of the caloric fluid caused the body to expand. To explain the liberation of heat when a block of metal was filed, it was postulated that small filings were less able to retain caloric, by virtue of their large surface area, than a block of solid metal. Attempts were made to measure the weight of caloric by trying to observe a change in the weight of a body when its temperature was raised, but these experiments were contradictory. Among others, Count Rumford (1753-1814), an American born Benjamin Thompson, who gained his title in the service of the Elector of Bavaria, found that the weight of a block of gold was unaltered by as much as 1 part in 1,000,000 when raised from the freezing point of water to bright-red heat.