2dly. That solutions of green sulphate of iron dissolve nitrous gas in quantities proportionable to their concentration, without effecting any decomposition of it at common temperatures. And the solubility of nitrous gas in solution of green sulphate, may be supposed to depend on an equilibrium of affinity, produced by the following simple attractions: 1. That of green oxide of iron for the oxygene of nitrous gas and water. 2. That of the hydrogene of the water for the nitrogene of the nitrous gas. 3. That of the principles of the sulphuric acid, for nitrogene and hydrogene. 3dly. That at high temperatures, that is, from 200° to 300°, the equilibrium of affinity producing the binary combination between nitrous gas and solution of green sulphate of iron is destroyed; the attraction of the green oxide of iron for oxygene being increased; whilst probably that of nitrogene for hydrogene is diminished. Hence the nitrous gas is either liberated,[123] in consequence of the affinity between oxygene and hydrogene, and oxygene and nitrogene not following the same ratio of alteration on increased temperature; or decomposed, because at a certain temperature the green oxide exerts such affinities upon water and nitrous gas, as to attract oxygene from both of them to form red oxide; whilst the still existing affinity between the hydrogene of the one, and the nitrogene of the other, disposes them to combine to form ammoniac. [123] Perhaps the liberation of nitrous gas from the solution takes place at a lower temperature than its decomposition. I have always observed that the quantity of yellow precipitate is greater when the solution is rapidly made to boil. Were it possible to heat it to a certain temperature at once, probably a compleat decomposition would take place. 4thly. That the change of color produced by introducing nitric acid to solution of common sulphate of iron, exactly analogous to that occasioned in it by impregnation with nitrous gas, is owing to the decomposition of the acid, by the combination of its oxygene with the green oxide of iron, and of its nitrous gas with the solution. 5thly. That nitrous gas in combination with solution of green sulphate of iron, is capable of exerting a strong affinity upon free or loosely combined oxygene, and of uniting with it to form nitric acid. _n._ The products obtained from a solution of sulphate of iron saturated with nitrous gas, by Vauquelin and Humbolt, and their consequent mistake with regard to the nature of the process of absorption,[124] must have arisen from exposure of their impregnated solution to the atmosphere. [124] Annales de Chimie. T. 38, pag. 187.