We have already seen, that the atmospheric air is composed of two gasses, or aeriform fluids, one of which is capable, by respiration, of contributing to animal life, and in which metals are calcinable, and combustible bodies may burn; the other, on the contrary, is endowed with directly opposite qualities; it cannot be breathed by animals, neither will it admit of the combustion of inflammable bodies, nor of the calcination of metals. We have given to the base of the former, or respirable portion of the air, the name of _oxygen_, from [Greek: oxys] _acidum_, and [Greek: geinomas], _gignor_; because, in reality, one of the most general properties of this base is to form acids, by combining with many different substances. The union of this base with caloric we term _oxygen gas_, which is the same with what was formerly called _pure_, or _vital air_. The weight of this gas, at the temperature of 10 deg. (54.50), and under a pressure equal to 28 inches of the barometer, is half a grain for each cubical inch, or one ounce and a half to each cubical foot. The chemical properties of the noxious portion of atmospheric air being hitherto but little known, we have been satisfied to derive the name of its base from its known quality of killing such animals as are forced to breathe it, giving it the name of _azote_, from the Greek privitive particle [Greek: a] and [Greek: xae], vita; hence the name of the noxious part of atmospheric air is _azotic gas_; the weight of which, in the same temperature, and under the same pressure, is 1 oz. 2 gros and 48 grs. to the cubical foot, or 0.4444 of a grain to the cubical inch. We cannot deny that this name appears somewhat extraordinary; but this must be the case with all new terms, which cannot be expected to become familiar until they have been some time in use. We long endeavoured to find a more proper designation without success; it was at first proposed to call it _alkaligen gas_, as, from the experiments of Mr Berthollet, it appears to enter into the composition of ammoniac, or volatile alkali; but then, we have as yet no proof of its making one of the constituent elements of the other alkalies; beside, it is proved to compose a part of the nitric acid, which gives as good reason to have called it _nitrigen_. For these reasons, finding it necessary to reject any name upon systematic principles, we have considered that we run no risk of mistake in adopting the terms of _azote_, and _azotic gas_, which only express a matter of fact, or that property which it possesses, of depriving such animals as breathe it of their lives.