Indeed, from the acidity of it, on examination, from the small portion of ammoniac, and the large quantity of nitric acid obtained, it appears most probable that the whole of the nitrous gas employed was converted into nitric acid, by combining with atmospheric oxygene; for no nitric acid could have been obtained in the mode in which they operated, unless the green oxide of iron in the solution had been previously converted into red. VIII. _On the absorption of Nitrous Gas by solution of green Muriate of Iron._ _a._ The analogy between the affinities of the constituents of the muriate and sulphate of iron, induced me to conjecture that they possessed similar powers of absorbing nitrous gas; and I soon found that this was actually the case; for on agitating half a cubic inch of solution of muriated iron, procured by dissolving iron filings in muriatic acid, in nitrous gas, the gas was absorbed with great rapidity, whilst the solution assumed a deep and bright brown tinge. _b._ Proust,[125] who as I have before mentioned, supposes the existence of two oxides of iron only, one containing ²⁷/₁₀₀ oxygene, the other ⁴⁸/₁₀₀, has assumed, that the muriatic acid, and most other acids as well as the sulphuric, are capable of combining with these oxides, and of forming with each of them a distinct salt. He has, however, detailed no experiments on the muriates of iron. [125] Annales de Chimie, xxiii. pag. 85; or Nicholson’s Phil. Journal vol. i. pag. 45. As these salts are still more distinct from each other in their properties than the sulphates, and as these properties are connected with the phænomenon of the absorption and decomposition of nitrous gas, I shall detail the observations I have been able to make upon them. _c._ When iron filings have been dissolved in pure muriatic acid, and the solution preserved from the contact of air, it is of a pale green color, and gives a white precipitate with alkaline prussiates. The alkalies throw down from it a light green oxide of iron. When evaporated, it gives crystals almost white, which are extremely soluble in water; but insoluble in alcohol. The solution of green muriate of iron has a great affinity for oxygene, and attracts it from the atmosphere, from nitric acid, and probably from oxygenated muriatic acid. When red oxide of iron is dissolved in muriatic acid, or when nitric acid is decomposed by solution of green muriate of iron; the red muriate of iron is produced. The solution of this salt is of a deep brown red, its odor is peculiar, and its taste, even in a very diluted state, highly astringent. It acts upon animal and vegetable matters in a manner somewhat analogous to the oxygenated muriatic acid, rendering them yellowish white, or yellow.[126] [126] Probably by giving them oxygene; whereas the green muriate and sulphate blacken animal substances; most likely by abstracting from them oxygene.