Joseph Black

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Joseph Black

Joseph Black (April 16, 1728 - December 6, 1799) was a Scottish physicist and chemist.

In 1744, he entered the University of Glasgow. Also, Black studied at Edinburgh University and then thoroughly studied properties of carbon dioxide. One of these studies was placing a flame and mice into the carbon dioxide. Because both entities died he concluded that the air was not breathable and named it `fixed air´ in 1754. In 1756 he described how carbonates become more alkaline when they lose carbon dioxide, whereas the taking-up of carbon dioxide reconverts them. He was the first person to isolate carbon dioxide in a perfectly pure state. This was an important step in the history of chemistry as it helped people to realize that air was not an element and was actually comprised of many different things. His work also aided in the discrediting of the belief in the actions of the fiery principle called phlogiston.

In the late 1750's he made an apparently innocuous experiment. He heated during the same time in an oven the same quantity of water and mercury and measured their respective temperatures. Surprisingly, the mercury was hotter than the water. He concluded that heat was a weightless fluid, invisible and indestructible and, according to his experiment, different materials had different capacities of absorbing and keeping heat. This theory was called the caloric theory and made possible to explain many observed phenomena. The interpretation of this experiment had disastrous consequences on the use of thermometers because its measurement may not be reproducible if the materials used in different thermometers were different. In other words, the measurement of the thermometers made with different materials (different glass, mercury with different purity...) coincide in the melting. However, the values do not necessarily coincide in the intermediate points as the materials behave differently when they are heated or cooled. This conclusion eventually led to the introduction of the absolute temperature that didn't depend on the properties of any material.

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

In 1761 he discovered that ice absorbs heat without changing temperature when melting. From this he concluded that the heat must have combined with the ice particles and become latent.

Between 1759 and 1763 he evolved that theory of "latent heat" on which his scientific fame chiefly rests, and also showed that different substances have different specific heats. James Watt was his pupil and assistant.

In 1755 he discovered that magnesium was a chemical element.

He was a member of the Poker Club and associated with David Hume, Adam Smith and the literati of the Scottish Enlightenment.