HENRY, William, a distinguished chemical philosopher, was born at Manchester, December 12, 1774. He was the son of Mr Thomas Henry, a zealous cultivator of chemical science. In early life an accident disqualified him for the sports of boyhood, and thus early developed a taste for study which was fostered by his first teacher, the Rev. Ralph Harrison, one of the best instructors of youth at that time in the north of England. On leaving Mr Harrison's academy, Henry became private secretary to Dr Percival, a physician of great general accomplishments and refined taste, who directed his course of reading with equal kindness and judgment. For five years he remained in the house of this valuable friend, and after some preliminary medical study in the infirmary of Manchester, removed, in 1795-6, to the University of Edinburgh, where some of the greatest masters of moral and physical science were then teaching. So powerful was the stimulus there given to his mental powers, that he often said, the rest of his life, active as it was, appeared a state of inglorious repose when contrasted with this season of unremitting effort. Prudential considerations obliged him to leave Edinburgh at the end of a year; but in 1805 he once more resumed his studies there, and two years later received his diploma of M.D. The interval between the two periods of his residence at Edinburgh was spent partly in the duties of medical practice at Manchester, and partly in superintending a chemical work commenced by his father, which gave him
great facilities for prosecuting original researches in his favourite science. In 1797 he sent to the Royal Society of London the first of a long series of scientific memoirs, with which he enriched the Transactions of that body. Its object was to re-establish the title of carbon to be ranked among elementary bodies, which had been denied by Austin, Beddoes, and other eminent chemists. He afterwards discovered a fallacy in his own reasoning, which he detected and exposed, in a subsequent memoir, before it was noticed by any other chemist. In 1800 he published in the Philosophical Transactions his experiments on muriatic acid gas. Previous to the discoveries of Davy oxygen was regarded as the sole principle of acidity; and muriatic acid was consequently believed to be composed of oxygen associated with an unknown radical. Henry's experiments had been made with the view of disengaging this imaginary element. When Davy's theory was propounded, many years after this date, Henry was one of the earliest converts. In 1803 he published his elaborate experiments on the quantity of gases absorbed by water at different temperatures, and under different pressures. The result of these was the establishment of the law that "water takes up of gas, condensed by one, two, or more additional atmospheres, a quantity which would be equal to twice, thrice, &c., the volume absorbed under the common pressure of the atmosphere." In 1808 (the year in which he became a Fellow of the Royal Society) Henry described in the Philosophical Transactions a form of apparatus adapted to the combustion of larger quantities of gases than could be fired in eudiometric tubes. This apparatus, though now superseded, gave more accurate results than had ever before been attained. In the following year, 1809, the Copley gold medal was awarded to him for his valuable contributions to the Transactions of the Royal Society. For the next fifteen years he continued his experiments on the gases, making known the results of them from time to time to the Society. In his last communication, in 1824, he claimed the merit of having conquered the only difficulty that remained in a series of experiments on the gaseous substances issuing from the destructive distillation of coal and oil, and proved the exact composition of the fire-damp of mines. Availing himself of the property (recently discovered by Döbereiner) in finely-divided platinum, of causing gaseous combinations, he proved the exact proportions which the residues, after the action of chlorine on oil and coal gases, bear to each other.
All the experiments of Dr Henry to which we have hitherto alluded bore upon æriformal bodies; but though these were his favourite subjects of study, his acquaintance with general chemistry is proved by his Elements of Experimental Chemistry to have been both sound and extensive. This work was one of the first on chemical science published in this country, which combined great literary elegance with the highest standard of scientific accuracy. His comparative analyses of many varieties of British and foreign salts were models of accurate analysis, and were important in dispelling the prejudices then popular in favour of the latter for economical purposes. His memoir on the theories of galvanic decomposition earned the cordial approval of Berzelius, as being among the first to maintain that view to which he himself pinned his faith.
It is to be regretted that Dr Henry did not contribute more to the literature of science. His biographical notices of his great contemporaries, Priestley, Wollaston, and Davy, have been justly pronounced as among the best examples of that kind of composition in the English language. His contrast between Davy and Wollaston may recall Playfair's celebrated contrast between Black and Hutton, both in the qualities common to the minds compared, and in the vigour which marks both compositions. Especially is it to be regretted that he did not live to carry out the great literary project for which he had collected materials—a history of
chemical discovery from the middle of the last century. Henryson. He could have made it one of the most popular books of science in our tongue. His son and biographer claims a very high degree of merit for his literary compositions, and particularly for his familiar letters. The concurrent testimony of all authorities proves that the general estimate of Dr Henry appended by his son, Dr Wm. Charles Henry, to his Biographical Account of the late Dr Henry, is by no means partial or overdrawn. "In the general intercourse of society Dr Henry was distinguished by a polished courtesy, by an intuitive propriety, and by a considerate forethought, and respect for the feelings and opinions of others; qualities arising out of the same high-toned sensibility that guided his tastes in letters, and that softened and elevated his whole moral frame and bearing. His comprehensive range of thought and knowledge, his proneness to general speculation in contradistinction to detail, his ready command of the refinements of language, and the liveliness of his feelings and imagination, rendered him a most instructive and engaging companion. To the young, and more especially to such as gave evidence of a taste for liberal studies, his manner was peculiarly kind and encouraging."
At intervals during his whole life Dr Henry suffered severely from the effects of the accident already mentioned which befell him in early life. This produced paroxysms of intense neuralgic agony, which rendered the extirpation of the principal nerves of the hand necessary: but this failed to afford the expected relief; and latterly, the irritation of the whole nervous system deprived him of sleep, and caused his death on September 2, 1836.