"Cavendish solved the problem... and whilst he avoided the confusion in which it involved others, he built upon it an additional great discovery. After ascertaining that the appearance of nitric acid was not dependent on the source from which the oxygen was prepared, and that the acid did not show itself unless more than a combining measure of oxygen was detonated with the hydrogen, he traced its production to the presence in the [eudiometer] of a little nitrogen, derived from the atmospheric air which had originally filled it, or had become mingled with the hydrogen and oxygen during their preparation or collection. He... verified this conclusion, by showing that the artificial addition of nitrogen to hydrogen, mixed with more than one-half its volume of oxygen, increased the amount of nitric acid produced at each detonation, and on the other hand, that if the hydrogen instead of the oxygen was in excess, no nitric acid appeared, although nitrogen was present."