"Thus far Cavendish appears rather as the follower of Black than as an independent observer, although... his investigation of the properties of free was equally original and accurate. He struck out, however... a new path... and added to the solitary fixed air, a second gas equally distinct from it and from atmospheric air in properties. This was , of which Cavendish cannot be called the discoverer, for many of his predecessors, Boyle among others, had encountered it; but no chemist had carefully examined its properties, or at least had described them."