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Joseph Black: “so pale, so gentle, so elegant and so illustrious”

A Joseph Black Building can be found on the campus of both the University of Edinburgh and the University of Glasgow. Each is home to one of the oldest chemistry departments in Britain and can trace some of their earliest successes to their scientific namesake.

Joseph Black (1728–1799) was born in Bordeaux, France, to an Irish wine merchant father and Scottish mother. He was schooled in Belfast and at 18 trained in medicine in Glasgow, finishing his education in Edinburgh. During his academic career he took positions at both universities.

In the latter part of the 18th century the Scottish Enlightenment was at its heady intellectual height and the scientific world revolved around Edinburgh. At the heart of this was the city’s renowned university that attracted students from across Europe. Between 1726 and 1785, over 20% of scientists active in England had spent some time in the city. The excitement and productivity of the time prompted Thomas Jefferson to declare that for science “no place in the world can pretend to be in competition with Edinburgh”.

At the historic English universities, Oxford and Cambridge, chemistry and natural philosophy were considered lesser disciplines. Chemistry was considered academically impure when compared to the classics and theology, tainted by its use in mining and metallurgy (study of metal extraction). With a more egalitarian attitude and a world leading medical school producing professional doctors, Edinburgh differed from Oxbridge in that it trained students for careers in the real world as well as in academia. The University of Edinburgh medical school was vital for promoting the sciences, particularly chemistry, as a worthy intellectual pursuit. Chemistry was compulsory for medical students and the majority of the Scottish chemists were active in medical practice.

One such chemist was Black’s tutor, William Cullen (1710–1790) who was celebrated for taking chemistry, “away from the application and made it a discipline for gentleman”. Cullen studied chemistry not for use in medicine or in agriculture but to construct a theory of chemical reactivity. He treated chemistry as an explanatory topic worthy of intellectual study. Black and Cullen lived in a period where scientific research was broadly termed natural philosophy. Only decades later would the term scientist be constructed to describe “a person using scientific methods”. Science had become professionalised as a result of the experimental analytical approach pioneered in the 18th century.

Black’s M.D. thesis was a true opus. In the search for a chemical cure to bladder stones, he explored the nature of heat, developed the use of the balance and most importantly discovered carbon dioxide. Though he didn’t find a cure for bladder stones, by heating magnesia alba (magnesium carbonate), he was able to collect a gas (carbon dioxide) which was chemically different from atmospheric air. He called the gas ‘fixed air’ as it was somehow contained within the magnesia alba. He weighed the magnesia alba before and after heating. Observing a weight loss he concluded that the missing mass was the gas that he had collected during heating.

Black’s successes depended on his tools. Indeed, though he was not the first to weigh chemicals, he crafted and refined his brass scales until they became the most accurate and precise in the world. Edinburgh’s chemistry department is home to a multitude of his scales which still compare favourably to modern standards.

Subsequently, Black turned his meticulous attention to the thermometer. Whilst obsessively testing liquids in search of the ideal thermometer fluid, Black spotted that when he boiled water or heated melting ice, his thermometer didn’t register any increase in temperature. This was the first reported observation of latent heat which would come to be understood as the amount of heat absorbed or emitted during a phase change. Latent heat fuelled the debate over heat, being claimed as definitive proof for French chemist Lavoisier’s new caloric theory; but however proponents of older theories were not convinced. Despite the importance of Black’s discovery, he rarely embroiled himself in these often speculative discussions.

Beyond the 1770s, Black’s scientific output faltered. Unmarried and sickly, he rarely ventured from Edinburgh, taking his holidays in a house on the Meadows. Nevertheless, he was not a forlorn character and remained an active, sociable member of Edinburgh’s intellectual scene, filling his time with teaching and assisting industry with practical problems.

His friendship would inspire James Watt in the development of the steam engine and hundreds flocked from across Europe to be taught by him. Among them was Thomas Beddoes, later a mentor to a young Humphry Davy who in turn would employ Michael Faraday. Though Black’s discoveries of carbon dioxide and latent heat assured his inclusion in the history of science, it was through his meticulous methods and inspirational teaching that he most influenced generations of chemists.

Alex Sinclair is a PhD student at the Centre for Science at Extreme Conditions


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