He begins with an account of a repetition of an experiment of Mr. Waltire’s, related by Priestley, in which a mixture of hydrogen and air was exploded in a copper vessel, with the result that they observed a loss of a few grains in weight; it is also stated by Waltire that if the explosion took place in a glass vessel, it became dewy, “which confirmed an opinion he had long entertained, that common air deposits its moisture by phlogistication.” But Cavendish, using a glass vessel of much greater capacity than Waltire’s, could remark no change of weight; and he concluded that 423 measures of hydrogen, or “inflammable air” as he named it, are “nearly sufficient to completely phlogisticate 1000 of common air, and that the bulk of the air remaining after the explosion is then very little more than ⅘ths of the common air employed; so that, as common air cannot be reduced to a much less bulk than that, by any method of phlogistication, we may safely conclude that, when they are mixed in this proportion and exploded, almost all the inflammable air, and about ⅕th part of the common air, lose their elasticity, and are condensed into the dew which lines the glass. “The better to examine the nature of this ‘dew,’ 500,000 grain measures of inflammable air were burnt with about 2½ times that quantity of common air, and the burnt air made to pass through a glass cylinder 8 feet long and about ¾ of an inch in diameter, in order to deposit the dew”. “By this means upwards of 135 grains of water were condensed in the cylinder, which had no taste or smell, and which left no sensible sediment when evaporated to dryness, neither did it yield any pungent smell during the evaporation; in short, it seemed pure water”. “And by this experiment it appears that this dew is plain water, and consequently that almost all the inflammable and about ⅕th of the common air are turned into pure water.” But on firing little by little a mixture of “dephlogisticated air” or oxygen, obtained from red precipitate (that is, mercuric oxide prepared by heating the nitrate), with twice its volume of “inflammable air” or hydrogen, the resulting water was acid to the taste, and on evaporation with alkali gave a small quantity--about 2 grains--of nitre. Cavendish suspected that the acid came from the nitrate of mercury in his red precipitate, and, to test this, procured his oxygen from other sources--from red-lead and sulphuric acid, and from the leaves of plants--but still with the same result; nitric acid was formed. Repeating the experiment so as to have present an excess of hydrogen, he found that no acid was produced.