HISTORY OF CHEMISTRY: Henry Cavendish (1731-1810).

Henry Cavendish (1731-1810), who, like Priestley, was of the phlogistic school, contributed by his discoveries and carefully conducted investigations, especially as regards gases, scarcely less than that experimenter to the advance in chemical knowledge which before the beginning of the 19th century effected the subversion of the Stahlian philosophy. To hum chemists are indebted for the invention of the pneumatic trough, and to him is due the first recognition of the importance of determining the specific gravities of the various gases. He established the radical difference between hydrogen and nitrogen, and discovered in 1781 that hydrogen and dephlogisticated air (oxygen), when exploded in a close vessel in proportions sufficient almost entirely to phlogisticate the burnt air, produced pure water; and that water was also formed when a mixture of common air and inflammable air was exploded, a reduction of one-fifth of the bulk of the former air being then observable. According to Cavendish, water consisted of phlogiston and dephlogisticated air; inflammable air, or phlogiston and water; the action of dephlogisticated upon inflammable air when exploded with it was to unite with its phlogiston to form water, and consequently to set free the water of the inflammable air; thus both airs became water. -- (Trans. Roy. Soc., 1784 and 1785). Lavoisier had shown in 1770 the incorrectness of the notion prevalent among chemists that water by continued boiling and redistillation could be transformed into an earth. Cavendish’s discovery deprived it of the rank of an element, to which, according to the vague Aristotelian doctrines of the time, it was entitled, and thus prepared the way for the acceptation of correct and definite views concerning the elementary bodies. Lavoisier, availing himself of the facts ascertained by Cavendish, taught that oxygen, the so-called dephlogisticated air, was an element, and that combined with it was imponderable caloric; inflammable air, or hydrogen, as he termed it, was another element, which had the power of disengaging from caloric a weight equal to its own of oxygen, with which it united to form water. The new doctrine did not, however, meet with very ready acceptance from the phlogistians. "It is inconceivable," writes one of them, "how water, which is absolutely incombustible, should have so combustible a body as inflammable gas is for one of its component parts; whereas, by admitting pure air in its whole substance to be one of the component parts of water, and the other to consist of the base only of inflammable gas, which being burnt by the passage of the electric spark through it, its phlogiston is converted into light and heat, the whole doctrine of the generation of water becomes plain and easy." – (Hopson, Chemistry, 1789.)






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