A minute quantity of oil of turpentine was introduced to 14 measures of nitrous oxide; it filled, in 4 minutes, a space rather less than 14; and no farther change took place afterwards. Most likely this contraction arose from the precipitation of the water dissolved in the gas by the stronger affinity of the oil for nitrous oxide. To ascertain with certainty if any oil had been dissolved by the gas, I introduced into it a small quantity of ammoniac. It immediately became slightly clouded, most probably from the formation of soap, by the combination of the dissolved oil with the ammoniac. From these experiments we learn, that when nitrous oxide is mingled with either carbonic acid, oxygene, common air, hydrocarbonate, sulphurated hydrogene, hydrogene, or nitrogene, they may be separated from each other without making any allowance for contraction or expansion; but if a mixture of either muriatic acid, or sulphureous acid gas, with nitrous oxide, is experimented upon; in the absorption of the acid by alkalies, the apparent volume of gas condensed will be less than the real one, by a quantity equal to the sum of expansion from combination. Consequently a correction must be made on account of this circumstance. Though alcohol, ether, essential oils, and the fluid inflammable bodies in general, dissolve nitrous oxide with much greater rapidity than water, yet as we are not perfectly acquainted with their action on unabsorbable gases, it is better to employ water for separating nitrous oxide from these substances; particularly as that fluid is more or less combined with all gases, and as we are acquainted with the extent of its action upon them. By pursuing the subject of the solution of essential oils in gases, we may probably discover a mode of obtaining them in a state of absolute dryness. For if other gases as well as nitrous oxide, have a stronger affinity for oils than for water, water most probably will be precipitated from them during their solution of oils; and after their saturation with oil, it is likely that they are capable of being deprived of that substance by ammoniac. VI. _Action of aëriform Nitrous Oxide in the Alkalies. History of the discovery of the combinations of Nitrous Oxide with the Alkalies._ _a._ When nitrous oxide in a free state is exposed to the solid caustic alkalies and alkaline earths, at common temperatures, it is neither absorbed nor acted upon; when it is placed in contact with solutions of them in water, a small quantity is dissolved; but this combination appears to depend on the water of the solution, for the gas can be expelled unaltered, at the temperature of ebullition. _b._ Caustic potash was exposed to nitrous oxide for 13 hours: the diminution was not to one fiftieth, and this slight condensation most probably depended upon its combination with the water of the gas.