Joseph Black

Joseph Black was the quiet revolutionary of the Scottish Enlightenment — a Glasgow chemist whose careful, patient experiments changed science twice over. He discovered carbon dioxide, the first gas ever shown to be chemically distinct from ordinary air, and he uncovered the hidden ‘latent’ heat that matter absorbs as it melts and boils. And it was that discovery, together with his own purse, that helped set his young university friend James Watt on the road to the improved steam engine that would drive the modern world.

This page tells his story: his origins and education, the discovery of fixed air, his Glasgow chair, his work on heat, his part in the making of the steam engine, his Edinburgh years, and his lasting importance.

A wine merchant’s son

Joseph Black was born in 1728 in Bordeaux, where his father, a merchant of Scots and Ulster descent, was engaged in the wine trade. Sent to school in Belfast to learn his Greek and Latin, he came at the age of sixteen to the University of Glasgow, where he studied the arts before turning to medicine. There he fell under the influence of a brilliant teacher, William Cullen, who lectured in chemistry — then a young and unfashionable science — and, unusually for a student, Black began to carry out original experiments in his professor’s laboratory. It was the making of him. To complete his medical degree he moved on to the University of Edinburgh, but the discoveries that would make his name were rooted in his Glasgow years.

The discovery of fixed air

For his Edinburgh medical thesis, awarded in 1754, Black studied a humble alkaline substance, magnesia alba — what we now call magnesium carbonate. In a series of exquisitely careful experiments, weighing his materials before and after heating, he showed that when the substance was heated it gave off a gas, and lost weight accordingly. That gas — which he named ‘fixed air’, and which we call carbon dioxide — was something wholly new to science. For Black had proved that ordinary air was not a single element, as had always been believed, but that distinct gases existed, each with its own properties. His fixed air was denser than common air, would not support a flame or animal life, and was produced by burning, by fermentation and by breathing. It was the first gas ever to be identified as a chemical substance in its own right, and it opened the door to the whole science of chemistry as we know it.

The Glasgow chair

In 1756, when Cullen moved to Edinburgh, Black succeeded him at Glasgow, taking up a professorship in medicine and lecturing in chemistry, and building a busy practice as a physician alongside his teaching. He was, by all accounts, a superb lecturer — lucid, precise and undemonstrative — and a careful, methodical experimenter rather than a flamboyant one. The Glasgow years, from the mid-1750s to the mid-1760s, were the most creative of his life. It was here, in the intellectual ferment of a university that was becoming one of the powerhouses of the Scottish Enlightenment, that he turned from the chemistry of gases to the physics of heat, and made his second great discovery.

The secret of heat

Black noticed something that others had missed. When ice melts, or water boils, it absorbs a great deal of heat — yet its temperature does not rise while the change is happening. The heat seemed to vanish, hidden, into the substance; Black called it ‘latent’ heat, and measured it with care. He saw, too, that different substances required different amounts of heat to warm them by the same degree — the property we call specific heat — and he was the first to draw a clear distinction between the quantity of heat in a body and its intensity, or temperature. In doing so he founded the accurate measurement of heat, and laid one of the cornerstones of the science that would later be called thermodynamics — a science carried on, a century afterwards, by Glasgow’s Lord Kelvin.

Black & James Watt

Among Black’s friends at Glasgow was a young instrument maker employed by the university, James Watt. Watt was struggling with the wasteful inefficiency of the steam engines of the day, which squandered vast amounts of heat, and it was Black’s idea of latent heat that helped him understand why — and so to conceive his great improvement, the separate condenser, which made the steam engine practical and powerful. Black’s help did not stop at ideas. He lent his friend money, and introduced him to the men of business who could finance his work. In backing Watt with both his science and his purse, the quiet Glasgow professor played a real and personal part in launching the Industrial Revolution.

Edinburgh & the Enlightenment

In 1766 Black followed Cullen once more, leaving Glasgow to become Professor of Chemistry at the University of Edinburgh, where he would remain for the rest of his life. There his fame as a lecturer drew students from across Europe and from America, though, curiously for so influential a man, he published very little; his ideas spread through his teaching and the notes of his pupils rather than through printed papers. He moved in the most brilliant company of the age, counting among his friends the philosopher David Hume, the economist Adam Smith and the geologist James Hutton — the leading figures of that extraordinary flowering of Scottish genius known as the Scottish Enlightenment.

The father of quantitative chemistry

Black’s influence on science was immense and lasting. His insistence on precise measurement — on weighing and quantifying everything — helped turn chemistry from a hotchpotch of recipes and speculation into an exact, quantitative science, and his discovery of fixed air paved the way for the chemical revolution completed by Lavoisier. When he died in Edinburgh in 1799, he left no great published treatise, but an example and a method that shaped generations of chemists after him. Fittingly, the chemistry buildings of both the universities he served, Glasgow and Edinburgh, bear his name to this day — a modest memorial to one of the founders of modern science.

A life in dates