Joseph Black

Joseph Black (16 April 1728 – 6 December 1799) was a Scottish physicist and chemist, known for his discoveries of magnesium, latent heat, specific heat, and carbon dioxide. He was Professor of Anatomy and Chemistry at the University of Glasgow for 10 years from 1756, and then Professor of Medicine and Chemistry at the University of Edinburgh from 1766, teaching and lecturing there for more than 30 years.

He was educated at home until the age of 12, after which he attended grammar school in Belfast. In 1746 at the age of 18 he entered the University of Glasgow, studying there for four years before spending another four at the University of Edinburgh, furthering his medical studies. During his studies he wrote a doctorate thesis on the treatment of kidney stones with the salt magnesium carbonate

Like most 18th-century experimentalists, Black's conceptualization of chemistry was based on five 'principles' of matter: Water, Salt, Earth, Fire and Metal. He added the principle of 'Air' when his experiments definitely confirmed the presence of carbon dioxide, which he called 'fixed air'. Black's research was guided by questions relating to how the 'principles' combined with each other in various different forms and mixtures. He used the term 'affinity' to describe the force that held such combinations together. Throughout his career he used a variety of diagrams and formulas to teach his University of Edinburgh students how to manipulate 'affinity' through different kinds of experimentation.

In about 1750, while still a student, Black developed the analytical balance based on a light-weight beam balanced on a wedge-shaped fulcrum. Each arm carried a pan on which the sample or standard weights was placed. It far exceeded the accuracy of any other balance of the time and became an important scientific instrument in most chemistry laboratories.

In 1757, Black was appointed Regius Professor of the Practice of Medicine at the University of Glasgow.

In 1761 he deduced that the application of heat to ice at its melting point does not cause a rise in temperature of the ice/water mixture, but rather an increase in the amount of water in the mixture. Additionally, Black observed that the application of heat to boiling water does not result in a rise in temperature of a water/steam mixture, but rather an increase in the amount of steam. From these observations, he concluded that the heat applied must have combined with the ice particles and boiling water and become latent.

The theory of latent heat marks the beginning of thermodynamics. Black's theory of latent heat was one of his more-important scientific contributions, and one on which his scientific fame chiefly rests. He also showed that different substances have different specific heats.

Carbon dioxide

Black also explored the properties of a gas produced in various reactions. He found that limestone (calcium carbonate) could be heated or treated with acids to yield a gas he called "fixed air." He observed that the fixed air was denser than air and did not support either flame or animal life. Black also found that when bubbled through an aqueous solution of lime (calcium hydroxide), it would precipitate calcium carbonate. He used this phenomenon to illustrate that carbon dioxide is produced by animal respiration and microbial fermentation.

Black was widely recognized as one of the most popular lecturers at the University. His chemistry course regularly attracted an exceptionally high number of students, with many attending two or three times. In addition to regularly introducing cutting-edge topics and meticulously selecting visually impressive experiments, Black employed a wide array of successful teaching tools that made chemistry accessible to his students (many of whom were as young as 14 years old). His students came from across the United Kingdom, its colonies and Europe, and hundreds of them preserved his lectures in their notebooks and disseminated his ideas after they left university.

Black never married. He died peacefully at his home in Edinburgh in 1799 at the age of 71 and is buried in Greyfriars Kirkyard.