This unexpected result obliged me to theorise a second time, by supposing that nitrate of ammoniac had been produced, which by combining with the white prussiate of iron, generated a new combination. But on mingling together green sulphate of iron, prussiate of potash, and nitrate of ammoniac in the atmosphere, the mixture remained perfectly white. To ascertain if any nitric acid existed, combined with any of the bases, in the impregnated solution, I introduced into it an equal bulk of diluted sulphuric acid: it became rather paler; but no green or blue tinge was produced. That the prussic acid had not been decomposed, was evident from the bright green produced, when less than a grain of dilute nitric acid was admitted into the solution. _f._ From these experiments it was evident, that no red sulphate of iron, or nitric acid, and consequently no ammoniac, had been produced after the absorption of nitrous gas by green sulphate of iron. And when I compared them with the observations of Priestley, who had expelled by heat a minute quantity of nitrous gas from an impregnated solution of common sulphate of iron, and who found common air phlogisticated by standing in contact with it, I began to suspect that nitrous gas was simply dissolved in the solution, without undergoing decomposition. _g._ To determine more accurately the nature of the process, I introduced into a mercurial cylinder 410 grains of solution of green sulphate of iron, occupying a space nearly equal to a cubic inch and quarter; it was saturated with nitrous gas, by absorbing 8 cubic inches. This saturated solution exhibited the same appearance as the last; and after remaining near an hour untouched, had evidently deposited no oxide of iron, nor gained any acid properties. Into a small mattrass filled with mercury, having a tight stopper with a curved tube adapted to it, the greater part of this solution was introduced; judging from the capacity of the mattrass, about 50 grains of it might have been lost. To prevent common air from coming in contact with the solution, the stopper was introduced into the mattrass under the mercury; the curved tube connected with a graduated cylinder filled with that substance; and the mattrass brought over the side of the mercurial trough. But in spite of these precautions a large globule of common air got into the top of the mattrass, from the curvature of the tube. When the heat of a spirit lamp was applied to the solution, it gave out gas with great rapidity, and gradually lost its color. When 5 cubic inches were collected it became perfectly pale green, whilst a yellow red precipitate was deposited on the bottom of the mattrass. On pouring a little of the clear solution into prussiate of potash, it gave only white prussiate of iron.