Interviewer: Joseph Black, you are a man who is well known in Edinburgh society, but do you not feel your professional reputation is undermined by the company you keep?
Black: Of an evening, I may pass the time in theological, philosophical and literary debate in one of Edinburgh’s many clubs with friends and colleagues such as Adam Smith, David Hume, James Hutton, James Watt and Alexander Carlyle. Such distinguished company only reinforces my professional reputation as a physician and university professor in the field of chemistry, which is my life’s passion.
Interviewer: You have discovered what you call latent heat. This concept is very difficult for the non-scientist like myself to understand. Are you actually able to explain it in simple terms?
Black: Of course! Every trade has its own language and science is no different. Latent heat is common in our everyday life, and can be explained in a way which is clear to everyone. For example, I discovered that when water is heated and boils, it doesn’t immediately turn to steam – it first absorbs the heat, without heating up. This “latent” heat is at the heart of thermo chemistry – the use of heat in science. This theory has been used to great effect by my colleague, James Watt, in his development of the power needed to drive his steam engine.
Interviewer: You have also discovered what you call specific heat. This just sounds like scientific jargon! If the ordinary man was able to understand what this was, would it be of any interest to him anyway?
Black: It certainly would! James Watt first sparked my interest in what happens to objects when they are heated, and I have discovered that different substances require different levels of heat to raise their temperatures. For example, it takes eight times more heat to raise the temperature of magnesium than it takes to heat lead, and this temperature is what I call the magnesium’s specific heat.
The greater the specific heat of an object, the more energy it takes to raise its temperature. And here, science is put to everyday use without most people being aware of it. When heating a substance, we obviously choose one with a lower specific heat as it takes less energy, and is therefore the more efficient and economical substance to use.
Interviewer: Do you never feel that you’re wasting your life on matters which are of no interest to anyone other than scientists?
Black: Not at all! The human race must learn and develop if it is to thrive and survive, and my work has contributed greatly to our understanding of the world around us. My work has been crucial in unlocking the secrets of chemistry, which in turn explains so many of the things we take for granted, and we can then apply this knowledge to our advantage. The air we breathe for example. My experiments in the burning of magnesium have led to a better understanding of this air and its make up. For many years, we had assumed that air was only one gas, but no longer, following my discovery of what I call “fixed air”, and what science now calls carbon dioxide. Isolating carbon dioxide in a pure state showed that the air we breathe is not an element, but composed of many different things. Now that we know what we breathe and what it is composed of, this knowledge can be used to develop of our understanding of our own bodies, and the atmosphere in which we live.
Interviewer: You claim that your passion for chemistry is undertaken for the good of all mankind. Very noble principles sir, but you are not by any stretch of the imagination a poor man and your passion has not exactly reduced you to poverty.
Black: Sir, I have never claimed to sacrifice all for my art. Science may be my passion but it is also my career, and as well as being a Professor of Chemistry, I make a well earned and well deserved living as a physician and doctor, which has not come without personal sacrifice and dedication.
I am an eminent medic and first physician to King George III in Scotland, holding the posts of Regius Professor of the Practice of Medicine; Professor of Anatomy and Botany; and Professor of Medicine, all at the University of Glasgow.
Interviewer: You hold important posts at Glasgow and Edinburgh Universities, and use these establishments for your research, but I would suggest that you use these seats of learning as your own scientific playgrounds. Do these universities benefit in any way from their association with you?
Black: These universities have invited me to use their facilities on the strength of my research and discoveries. They hope that any advances made on their premises will assure that university even greater academic recognition. I lecture five days a week, for five months of the year, to two hundred students per day, and although I do receive an income of three guineas from each student, my work at the university is unsalaried. As a teacher, I am both popular and effective, and my lectures are practical demonstrations, illustrated by experiments based on my current research.
Interviewer: And what, Joseph Black, is your contribution to society… your legacy to the world?
Black: I have been personally responsible for the discoveries of latent heat, specific heat and carbon dioxide which have revolutionised scientific thinking. In turn, this has increased our understanding of the world in which we live and breathe. These discoveries have also inspired engineers such as James Watt in the development of the steam engine.
Many of the five thousand students that I have taught have gone on to hold Chairs of Chemistry in Edinburgh, Glasgow, Cambridge and Oxford, and many have made significant contributions to science.
Perhaps my legacy can be summed up in the words of the great chemist, Lavoisier, who described himself as ‘one of the most zealous admirers of the depth of my genius and of the important revolutions which my discoveries have caused in the Sciences’.
An actor portrays the 18th century Scottish scientist Joseph Black in this video, explaining his discoveries in chemistry which underpinned new inventions in engineering and industry.
One of the great chemistry teachers and researchers of the age, Joseph Black promoted the science of thermodynamics, discovering carbon dioxide, which he called 'fixed air'.