_h._ To determine if any nitrogene had entered into chemical combination with muriatic acid and oxygene, so as to form an aëriform triple compound, analogous in its properties to oxygenated muriatic acid, I exposed some of the gas to mercury, expecting that this substance, by combining with its oxygene, would effect a complete decomposition; and this was actually the case: for the gas was at first rapidly diminished, and the mercury became oxydated; its volume, however, soon increased; and the residual gas appeared to be nitrous, mingled with much nitrogene. The exact proportions of each, from an accident, I could not determine. This experiment was inconclusive, because the nitro-muriatic acid suspended in the peculiar gas, from which it can probably be never perfectly freed, acted in common with it upon the mercury, and produced nitrous gas: and this nitrous gas, at the moment of its production, formed nitrous acid by combining with the oxygene of the peculiar gas; and the nitrous acid generated[149] was again decomposed by the mercury; and hence nitrous gas evolved, and possibly some nitrogene. [149] The decomposition of aëriform nitrous acid by mercury, was first noted by Priestley; vol. iii. pag. 101. This decomposition I have often had occasion to observe. In reading Humbolt’s paper on eudiometry, Annales de Chimie, xxviii, pag. 150, I was not a little surprised to find that he takes no notice of this fact. He seems to suppose that nitrous acid can remain aëriform, and even be condensed, in contact with mercury, without alteration. He says, “In mingling 100 parts of atmospheric air with 100 of nitrous air, the air immediately became red, but all the acid produced remained aëriform; and after eighteen hours some _drops_ only of acid were formed, which _swam_ upon the mercury.” _i._ Peculiar circumstances prevented me at this time from completely investigating the subject. It remains doubtful whether the gas consists simply of highly oxygenated muriatic acid and nitrogene,[150] produced by the decomposition of nitric acid from the coalescing affinities of platina and muriatic acid for oxygene; or whether it is composed of a _peculiar_ gas, analogous to oxygenated muriatic acid, and nitrogene, generated from some unknown affinities.[151] [150] Lavoisier has said concerning aqua regia, “In solutions of metals in this acid, as in all other acids, the metals are first oxydated, by attracting a part of the oxygene from the compound radical. This occasions the disengagement of a particular species of gas not hitherto described, which may be called nitro-muriatic gas. It has a very disagreeable smell, and is fatal to animal life when respired; it attacks iron, and causes it to rust; it is absorbed in considerable quantities by water.” Elem. Eng. 237. [151] I have no doubt but that the gas procured from the solution of gold in aqua regia, is analogous to that produced from platina.