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Black, Joseph

heat chemistry formulae compounds

(1728–99) British physician, chemist and physicist: pioneer of modern chemical logic; discoverer of latent heat and specific heat.

Black was born in Bordeaux, where his Scots-Irish father was a wine merchant. Joseph was educated in Belfast, Glasgow and Edinburgh. Finally, he studied medicine. His work for his MD degree, expanded in a paper of 1756, is his major contribution to chemistry; it is a model of experiment and logic. In particular, he saw the importance of recording changes of weight and he recognized the importance of gases. He studied the cycle of changes we would now express in formulae as follows: (note that Black knew his compounds by the names given in brackets; formulae and atomic theory came much later, but he understood the key relationships between the compounds):

Black showed that fixed air (CO2 ) is produced by respiration and fermentation, and by burning char-coal; that it behaves as an acid (eg in neutralizing an alkali); and he deduced its presence in small quantities in the atmosphere. He was a very popular lecturer at Glasgow and later in Edinburgh; one of his pupils was Benjamin Rush (1745–1813), who became the first professor of chemistry in America.

He taught new views on chemistry when they appeared, but his own research moved to physics. About 1763 he showed that heat is necessary to produce a change of state from solid to liquid, or liquid to vapour, without a rise in temperature; e.g., ice at 0° requires heat to form water at 0°. He called this ‘latent heat’. On this basis, he went on to distinguish clearly between heat and temperature; and he examined the different heat capacity of substances. Thus in physics, as in chemistry, he provided basic ideas essential for the subject to advance.

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