Joseph Black

SCOTTISH CHEMIST AND PHYSICIST
1728–1799

Joseph Black was trained as a medical doctor. One of his early scientific undertakings was investigating means of treating "the stone" (kidney stones and gallstones). The investigation prompted him to make a study of how to dissolve stones found in nature. Black found that certain stones, such as limestone, dissolved in mild acids, giving off large volumes of a gas. He called this gas "fixed air," as it had been "fixed" in a small volume of solid stone. Following the practice of the pneumatic chemists (chemists who were studying the properties of gases or "airs"), he trapped and characterized this new gas. "Fixed air" was found to be mildly acidic. It would later be called carbon dioxide, and stones that generated this gas would be defined as carbonates. Black also discovered that the chemical nature of the gas that had been produced in these experiments was determined by the stone it came from, not by the acid used.

Black was the first to distinguish between the temperature of an object and the heat contained in that object. He characterized "specific heat" as the amount of heat required to increase the temperature of a sample by a given amount. He recognized that it is dependent on the identity of and the amount of the material in the sample. If the sample being heated is at its melting or boiling temperature prior to the application of heat, it will absorb heat as it is going through a phase change (from solid to liquid or liquid to gas), but the temperature of the sample does not increase. The amount of heat absorbed during such a transition is also dependent on the amount of material in the sample and is characteristic of the type of material in the sample. Black termed this heat "latent heat" because it is "latent" in the sample and does not increase the temperature of the sample.

Although trained as a medical doctor, Joseph Black spent most of his professional career as an instructor in chemistry at the University of Edinburgh. His lecture notes were edited by one of his students and published as a textbook in chemistry in 1803, four years after his death.

David A. Bassett

Bibliography

Partington, J. R. (1962; reprint 1996). A History of Chemistry , Vol. 3. New York: Martino Publishing.