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wonderful discoveries of oxygen, chlorine, and barytes. This work put him on the track of the observations set forth in his famous work on "Air and Fire." In this he explained the composition of the atmosphere, which, he said, consisted of two gases, one of which he named "empyreal" or "fire-air," the same as he had obtained from black oxide of manganese, and other substances. He realised and described with much acuteness the part this gas played in nature, and the rest of the book contained many remarkable observations which showed how nearly Scheele approached the new ideas which Lavoisier was to formulate only a few years later. "Air and Fire" was not issued till 1777, three years after Priestley had demonstrated the separate existence and characteristics of what he termed "dephlogisticated air." But it is well known that the long delay of