But the origin of the acid in water made from inflammable and dephlogisticated air was still unexplained. To settle this point Cavendish added to an explosive mixture of oxygen and hydrogen a tenth of its volume of nitrogen, and found that the water was much more strongly acid; and if hydrogen was much in excess, a still greater amount of nitric acid was produced. After relating these experiments he proceeds:-- “From what has been said there seems the utmost reason to think that dephlogisticated air is only water deprived of its phlogiston, and that inflammable air, as was before said, is either phlogisticated water or else pure phlogiston, but in all probability the former.” In a foot-note he gives his reason for the choice, viz. that it requires a red-heat to cause hydrogen and oxygen to combine, while nitrous air combines with oxygen at the ordinary temperature; now, if hydrogen were pure phlogiston, one would expect it to combine more readily than nitrous gas, which has been shown to be a compound of nitric acid with phlogiston. It seems inexplicable that dephlogisticated air should refuse to unite at the ordinary temperature with pure phlogiston, when it is able to extract it from substances with which it has an affinity. Hence it is unlikely that hydrogen is phlogiston itself. And a few paragraphs farther on Cavendish very nearly discards the phlogistic theory by this statement: “Instead of saying air is phlogisticated or dephlogisticated by any means, it would be more strictly just to say, it is deprived of, or receives, an addition of dephlogisticated air; but as the other expression is convenient, and can scarcely be considered as improper, I shall still frequently make use of it in the remainder of this paper.” And now we come to the consideration of Lavoisier’s new theory, and its rejection in favour of the old one of phlogiston. It is curious to follow the reasoning which made such an exceptionally acute thinker as Cavendish deliberately reject the true explanation. Cavendish first states his results in Lavoisier’s terms:--