In 1772 he communicated privately to Dr. Priestley the results of a series of experiments dealing with nitrogen. To prepare it, he passed air repeatedly over red-hot charcoal, and absorbed the resulting carbon dioxide in potash. The residue was nitrogen. His description of it is:--“The specific gravity of this air was found to differ very little from that of common air; of the two it seemed rather lighter. It extinguished flame, and rendered common air unfit for making bodies burn in the same manner as fixed air, but in a less degree, as a candle which burned about 80 seconds in pure common air, and which went out immediately in common air mixed with 6/55ths of fixed air, burned about 26 seconds in common air mixed with the same proportion of this burnt air.”[23] He named it, as usual, “mephitic air,” and it is certain that, although Cavendish did not publish his results, his discovery was not later in date than Rutherford’s. Dealing next with the phenomena observed when that curious fish, the torpedo, produces shocks, he ascribed them to the discharge of electricity, and he was the first to distinguish between intensity, or potential, and quantity of electricity, a distinction now familiar to all. It was in 1777 that he commenced his beautiful “Experiments on Air,” the first account of which was published in 1783. They led to the discovery of the constant quantitative composition of the atmosphere, of the compound nature of water, and of the composition of nitric acid, and pointed the way to the recent discovery of argon.