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Black, Joseph (1728-1799).

Experiments upon magnesis alba, quicklime, and some other alcaline substances.
Edinburgh, 1770.

"A founder of modern quantitative chemistry and discoverer of latent and specific heats, Joseph Black, although born in France, was by blood pure Scot. Preoccupied at first with his medical studies, Black did not come to grips with his chosen problem until late in 1753. He chose a white powder, magnesia alba, recently in vogue as a mild purgative. Its preparation and general properties had been described by Hoffmann; although it resembled the calcareous earths, magnesia alba was clearly distinguishable from them. Could a product similar to quicklime be formed by calcining magnesia alba? Would its solutions have the causticity and solvent power of limewater? Black's effort to test this possibility was the turning point of his research. The properties of this substance now commanded Black's entire attention, notably the marked decrease in weight that resulted when magnesia alba changes into magnesia usta. What was lost? Using the balance more systematically than any chemist had done before him, he performed a series of quantitative experiments with all the accuracy he could command. From this Black showed that a particular kind of air, different from common air, can be a quantitative constituent of ordinary substances and must enter, as Lavoisier put it late, into their 'definition'. In mid career he told his students, well before the fulfillment of what we call the chemical revolution: Upon the whole, Chymistry is as yet but an opening science, closely connected with the useful and ornamental Arts, and worthy the attention of a liberal mind. And it must always become more and more so: for though it is only of late, that it has been looked upon in that light, the great progress already made in Chymical knowledge, gives us a pleasant prospect of rich additions to it. The Science is now studied on solid and rational grounds. While our knowledge is imperfect, it is apt to run into errour: but Experiment is the thread that will lead us out of the labyrinth" (Dictionary of Scientific Biography).

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