I. Density of Nitrogen from Various Sources. In a former paper it has been shown that nitrogen extracted from chemical compounds is about ½ per cent. lighter than “atmospheric nitrogen.’’ The mean numbers for the weights of gas contained in the globe used were as follows:— Grams. From nitric oxide...................... 2⋅3001 From nitrous oxide...................... 2⋅2990 From ammonium nitrite ...... 2⋅2987