f. In an experiment that I made to ascertain the quantity of nitrous gas capable of combining with solution of green muriate of iron; I found that,75 cubic inches of saturated solution absorbed about 18 of nitrous gas, which is nearly double the quantity combinable with an equal portion of the strongest solution of sulphate of iron. A part of this impregnated solution, heated slowly, gave out more gas in proportion to the quantity it contained, than the last, and consequently produced less precipitate; so that I am inclined to suppose it probable, that at a certain temperature, all the dissolved nitrous gas may be dispelled from a solution.
From these experiments we may conclude,
1st. That the solution of green muriate of iron absorbs nitrous gas in consequence of nearly the same affinities as solution of green sulphate of iron; its capability of absorbing larger quantities depending most probably on its greater concentration (that is, on the greater solubility of the muriate of iron), and perhaps, in some measure, on a new combining affinity, that of muriatic acid for oxygene.
2dly. That at certain temperatures nitrous gas is either liberated from solution of green muriate, or decomposed, by the combination of its oxygene with green oxide of iron, and of its nitrogene with hydrogene, produced from water decompounded by the oxide at the same time.
IX. Absorption of Nitrous Gas by
Solution of Nitrate of Iron.
a. As well as two sulphates and two muriates of iron, there exist two nitrates.[127] When concentrated nitric acid is made to act upon iron, nitrous gas is disengaged with great rapidity, and with great increase of temperature: the solution assumes a yellowish tinge, and as the process goes on, a yellow red oxide is precipitated.
Nitrate of iron made in this way, gives a bright blue mingled with prussiate of potash, and decomposed by the alkalies, a red precipitate. Its solution has little or no affinity for nitrous gas.
b. When very dilute nitric acid, that is, such as of specific gravity 1,16, is made to oxydate iron, without the assistance of heat, the solution gives out no gas for some time, and becomes dark olive brown: when neutralised it gives, decomposed by the alkalies, a light green precipitate; and mingled with prussiate of potash, pale green prussiate of iron.
It owes its color to the nitrous gas it holds in solution. By exposure to the atmosphere it becomes pale, the nitrous gas combined with it being converted into nitric acid.
It is then capable of absorbing nitrous gas, and consists of pale nitrate of iron, mingled with red nitrate.