I procured a solution of red sulphate of iron, by passing oxygenated muriatic acid through a solution of common sulphate of iron, till it gave only a red precipitate, when mingled with caustic potash. To nitrous gas confined by mercury, a small quantity of this solution was introduced. On agitation, its color altered to muddy green; but the absorption that took place was extremely trifling: in half an hour it did not amount to,2, the volume of the solution being unity, when it had nearly regained the yellow color. I now obtained a solution of green sulphate of iron, by dissolving iron filings in diluted sulphuric acid. The solution was agitated in contact with sulphurated hydrogene, and afterwards boiled; when it gave a white precipitate with prussiate of potash. A small quantity of this solution agitated in nitrous gas, quickly became of an olive brown, and the gas was diminished with great rapidity; in two minutes, a quantity equal to four times the volume of the solution, had been absorbed. These facts convinced me that the solubility of nitrous gas in common sulphate of iron, chiefly depended upon the pale green sulphate contained by it; and that the attraction of one of the constituents of this substance, the green oxide of iron, for oxygene, was one of the causes of the phænomenon. _d._ Green sulphate of iron rapidly decomposes nitric acid. It was consequently difficult to conceive how any affinities existing between nitrous gas, water, and green sulphate of iron, could produce the nitric acid found in the experiments of Vauquelin and Humbolt. To ascertain if the presence of a great quantity of water destroyed the power of green sulphate of iron to decompose nitric acid, I introduced into a cubic inch of solution of green sulphate of iron, two drops of concentrated nitric acid. The solution assumed a very light olive color; prussiate of potash mingled with a little of it, gave a dark green precipitate. Hence the nitric acid had been evidently decomposed. As no nitrous gas was given out, which is always the case when nitric acid is poured on crystalised sulphate of iron, I suspected that a compleat decomposition of the acid had taken place; but when the solution was heated, a few minute globules of gas were liberated, and it gradually became slightly clouded. Having often remarked that no precipitation is ever produced during the conversion of green sulphate of iron into red, by oxygenated muriatic acid, or concentrated nitric acid, I could refer the cloudiness to no other cause than to the formation of ammoniac. To ascertain if this substance had been produced, a quantity of slacked caustic lime was thrown into the solution. On the application of heat, the ammoniacal smell was distinctly perceptible, and the vapor held over orange nitrous acid, gave dense white fumes.