ingenious experiments, proved that the nitric acid was formed from the atmospheric nitrogen present in the detonating globe, and demonstrated that the only product of the combustion of pure hydrogen and oxygen was pure water. In his own words he came to the conclusion ‘that water consists of dephlogisticated air (oxygen) united with phlogiston (hydrogen).’ He was thus the first who, by purely inductive experiments, converted oxygen and hydrogen into water, and who taught that water consisted of these gases. He must also be regarded as the discoverer of nitric acid. In the history of chemistry we do not find any discovery which has led to the same amount of angry discussion as that which followed the important announcement by Cavendish in his ‘Experiments on Air,’ which were begun in 1777 or 1778, but which were not published until 1783.
On 15 Jan. 1784 the ‘Experiments on Air, by Henry Cavendish, Esq.,’ was read before the Royal Society. An interpolation by Dr. Blagden (who for some time acted as secretary to Cavendish), after the paper was read, states that all the experiments on the explosion of inflammable air with common and dephlogisticated airs were made in the summer of 1781. Cavendish himself commences his paper ‘Experiments on Air’ by stating that his experiments were made ‘with a view to find out the cause of the diminution which common air is well known to suffer, by all the various ways in which it is phlogisticated, and to discover what becomes of the air thus lost or consumed.’ To this he adds subsequently that his experimental results, beyond ‘determining this fact, also throw light on the constitution and means of production of dephlogisticated air.’ This question excited much attention among the chemists of Europe in 1777. Priestley and Scheele about the same time discovered oxygen, and this gas was regarded by them as air perfectly respirable, and exhibiting its great power of supporting combustion, because it was deprived of phlogiston. It was, in accordance with this hypothesis, named by chemists dephlogisticated air. For some time the atmosphere was believed to consist of two parts of dephlogisticated air (our oxygen) and one part of phlogisticated air (our nitrogen). Cavendish resolved on ascertaining with precision the true constitution of the aerial fluid. With this object in view he burnt various bodies in measured quantities of air, confined over water at first, and then over mercury. As early as 1766 Cavendish had satisfied himself of the constant composition of the atmosphere. With his usual care he prosecuted this inquiry. Dr. Priestley and his friend Warltire repeated and modified Cavendish's experiments, and in 1781 Priestley refers to Warltire's observations on the moisture left by burning inflammable air. Warltire is said to have burned the gases in a close vessel by means of electricity, weighing the vessel before and after the explosion, observing the dewy deposit and finding only a very trifling loss of weight. Mr. James Patrick Muirhead, in his ‘Correspondence of the late James Watt,’ volunteers the information that there appears ‘no conclusion as to the real origin of water published (in 1781) by Mr. Cavendish, nor communicated to any individual, nor contained in the journal and notes of his experiments; nor alleged by himself, nor by any one else, to have been then drawn by him.’ In 1766 Cavendish employed hydrogen and air, and he then noticed ‘a certain amount of liquid’ being found in the flask in which the gases were exploded, and he unhesitatingly concludes that ‘almost all the inflammable air, and about one-fifth of the common air, lose their elasticity and are condensed into the dew which lines the glass.’ His full conclusion was ‘that this dew is plain water, and consequently that almost all the inflammable air, and about one-fifth of the common air, are turned into pure water.’ Watt, Dr. Priestley, Dr. Black, Mr. de Luc, M. la Place, M. Lavoisier, and others were deeply interested in the phlogistic hypothesis, and all of them were in constant communication, meeting in scientific societies or corresponding with each other. Cavendish, it must be regretted, did not pursue his brilliant career with any activity. He led a strangely retired life, and consequently he frequently was left in ignorance of the progress of discovery. Cuvier, in his éloge on Cavendish, said of him, ‘his demeanour and the modest tone of his writings procured him the uncommon distinction of never having his repose disturbed either by jealousy or by criticism.’
Arago, on the contrary, brought before the French Academy of Sciences a direct charge of deceit and plagiarism, affirming that Cavendish learned the composition of water by obtaining a sight of a letter from Watt to Priestley.
The researches of Cavendish were communicated to Dr. Priestley before 24 June 1781; even Watt's son does not doubt this. On 26 March 1783 Watt mentions as new to him Priestley's experiment on exploding the gases by electricity. On 21 April in the same year Watt writes to Dr. Black, and on 26 April to Dr. Priestley, his conclusion
