In December, 1799, designing to make a very delicate experiment, with a view to ascertain if any water was decomposed during the conversion of nitrous gas into nitrous oxide, by sulphite of potash, I exposed 200 grains of crystalised sulphite of potash, containing great superabundance of alkali, to 14 cubic inches of nitrous gas, containing one eighteenth nitrogene. The alkali was employed to preserve any ammoniac that might be formed, in the free state, as it would otherwise combine with sulphureous acid.[156] [156] Sulphureous acid saturates more potash than sulphuric acid, so that most probably during the conversion of sulphite of potash into sulphate, portions of sulphureous acid are disengaged. The volume of gas diminished with great rapidity; in two hours and ten minutes it was reduced to 6⁴/₅, which I considered as the limit of diminution. Accidentally, however, suffering it to remain for three hours longer, I was much surprised by finding that not quite 2 cubic inches remained, which consisted of nitrous oxide, mingled with the nitrogene that existed before the experiment. In accounting theoretically for this phænomenon, different suppositions necessarily presented themselves. 1st, It was possible, that though sulphite of potash, and potash, separately possessed no action on free nitrous oxide, yet in combination they might exert such affinities upon it as either to absorb it, or make it enter into new combinations. 2dly. It was more probable that the caustic potash, though incapable of condensing aëriform nitrous oxide, was yet possessed of a strong affinity for it when in the _nascent state_, and that the nitrous oxide condensed in the experiment had been combined in this state with the free alkali. To ascertain if the compound of potash and sulphite of potash with sulphate, was capable of acting upon nitrous oxide, I suffered a quantity of this substance to remain in contact with the gas for near a day: no change whatever took place. To determine whether the diminution of nitrous oxide depended upon its absorption in the nascent state, by the peculiar compound of potash and sulphite of potash, or if it was simply owing to the alkali. I mingled a solution of sulphite of potash with caustic soda; the salt, after being evaporated at a low temperature, was exposed to nitrous gas. The nitrous oxide formed was absorbed, but in rather less quantities than when alkaline sulphite of potash was employed. Hence it was evident that the alkali was the agent that had condensed the nitrous oxide in those experiments, for soda is incapable of combining either with sulphate, or sulphite of potash.