The azotic gas may be procured from atmospheric air, by absorbing the oxygen gas which is mixed with it by means of a solution of sulphuret of potash, or sulphuret of lime. It requires twelve or fifteen days to complete this process, during which time the surface in contact must be frequently renewed by agitation, and by breaking the pellicle which forms on the top of the solution. It may likewise be procured by dissolving animal substances in dilute nitric acid very little heated. In this operation, the azote is disengaged in form of gas, which we receive under bell glasses filled with water in the pneumato-chemical apparatus. We may procure this gas by deflagrating nitre with charcoal, or any other combustible substance; when with charcoal, the azotic gas is mixed with carbonic acid gas, which may be absorbed by a solution of caustic alkali, or by lime water, after which the azotic gas remains pure. We can procure it in a fourth manner from combinations of ammoniac with metallic oxyds, as pointed out by Mr de Fourcroy: The hydrogen of the ammoniac combines with the oxygen of the oxyd, and forms water, whilst the azote being left free escapes in form of gas. The combinations of azote were but lately discovered: Mr Cavendish first observed it in nitrous gas and acid, and Mr Berthollet in ammoniac and the prussic acid. As no evidence of its decomposition has hitherto appeared, we are fully entitled to consider azote as a simple elementary substance. TABLE _of the Binary Combinations of Hydrogen with Simple Substances._ _Simple_ _Resulting Compounds._ _Substances._ _New Nomenclature._ _Old Names._ Caloric Hydrogen gas Inflammable air. Azote Ammoniac Volatile Alkali. Oxygen Water Water. Sulphur {Hydruret of sulphur, or } {sulphuret of hydrogen } Hitherto unknown (A). Phosphorus {Hydruret of phosphorus, or } {phosphuret of hydrogen } Charcoal {Hydro-carbonous, or } Not known till lately. {carbono-hydrous radicals(B)} Metallic {Metallic hydrurets(C), as } Hitherto unknown. substances, {hydruret of iron, &c. } as iron, &c. { } [Note A: These combinations take place in the state of gas, and form, respectively, sulphurated and phosphorated oxygen gas--A.] [Note B: This combination of hydrogen with charcoal includes the fixed and volatile oils, and forms the radicals of a considerable part of the vegetable and animal oxyds and acids. When it takes place in the state of gas it forms carbonated hydrogen gas.--A.] [Note C: None of these combinations are known, and it is probable that they cannot exist, at least in the usual temperature of the atmosphere, owing to the great affinity of hydrogen for caloric.--A.] SECT. VII.--_Observations upon Hydrogen, and its Combinations with Simple Substances._