1360. Oxygen and azote, or nitrogen, are the remaining constituents of the atmosphere. After a given portion of common air has been deprived of aqueous vapour and carbonic acid gas, it appears little altered in its properties; it remains a mixture of oxygen and azote, which supports combustion and animal life. There are many modes of separating these two gases from each other. A simple one is by burning phosphorus in a confined volume of air; this absorbs the oxygen and leaves the azote; and 100 parts in a volume of air, in which phosphorus has been burnt, yield seventy-nine parts of azote; and by mixing this azote with twenty-one parts of fresh oxygen gas artificially procured, a substance having the original characters of air is produced. To procure pure oxygen from air, quicksilver may be kept heated in it, at about 600ﾦ, till it becomes a red powder; this powder, which is an oxide of mercury, when ignited, will be restored to the state of quicksilver by giving off oxygen.
