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of its properties defcribed. It has been theredated to be an oxyd of azot, or to confift of azotunited with a certain portion of oxygen but notfuificient to conftitute nitric acid. On theother hand there is another fubflance the nitrousoxyd , or gaffeous oxyd of azot alfo compofed ofazot and oxygen, but in which the latter is infmaller proportion than in nitrous gas; fo thatnitrous gas is intermediate between the two,and being readily decompofable by a variety ofchemical agents (both thofe that give and thofethat take away oxygen) the production ofnitrous oxyd or of azot on the one hand, and-of nitric acid on the other, is always to be fought.for in all experiments on nitrous gas.

The nature of this gas was firft explained byDr. Prieftley who {hewed it to be a conftituentof nitric acid, and {hewed how it was convertedinto this acid, that is, by union with oxygen,and hence he ingenioufly applied it to theanalylis of air containing oxygen, as has beenalready defcribed under the article Eudiometry.Since his time this gas with all its varieties hasbeen the fubjecl of a great number of ablerefearches, and its properties have been veryfully explained.

Nitrous gas is obtained molt convenientlyduring the folution of fome of the metals innitric acid. Moft of the metals are added onby this acid and decompofe it, but in theprocefs fome of them produce nitrous gas nearlypure; others, a mixture of nitrous gas andnitrous oxyd, and others nitrous oxyd nearlypure. The degree of concentration of the acidalfo and the temperature have a great effeft onthe gafl'eous product, for, when thefe are fuchas to produce a very violent adtion, red nitrousvapour is alfo given out, and the produdts aredifferent from thofe that occur with a floweradtion.

Copper and mercury are the metals that■produce the pureft nitrous gas. Shreds ofcopper, or a fmall quantity of mercury, Ihouldbe put into a bottle with a curved tube and thebottle nearly filled with an acid of fuch llrengthas to a£t moderately fall at a heat tolerable tothe hand, which will be made by diluting theconcentrated acid with about three parts ofwater. .As the metal diflblves, the nitrous gasis given out, and after a fmall .quantity has runto wafte to difplace the air of the veflel, the gasmay be colledled in jars over water. Duringthe procefs a gentle heat may be ufed to haftenthe produdtion of gas. By this method nitrousgas may be procured fo pure as not to contain

more than to yV of impurity, which 5 *azotic gas. According to Mr. Davy ioo cubicinches of this gas at 56° therm, and 30.9 bar.weigh 31.3 grains, which at 55 0 therm, and30 bar. would weigh 34.26 grains.

Nitrous gas therefore is heavier than commonair, according to Davy in the proportion of1101.6 to 1000. 100 inches of common airweighing 31.1 in the fame circumftances inwhich nitrous gas weighs 34.26.

Nitrous gas is to a certain degree abforbableby water. 100 cubic inches of the pureftwater deprived of the air it naturally containsby long boiling, and cooling-over mercury, (thatit may not again abforb air from the atmofphere)will abforb about 11.8 of nitrous gas or fome-what more than -j- of its bulk. Common fpringwater abforbs a fmaller quantity, but the ab-forption however appears lefs than it really is,as the gas is partly decompofed by the atmo-fpher cal air contained in all natural waters, andthe azot of this air is given out, whilft itsoxygen forms nitric acid with the abforbednitrous gas. Water faturated with nitrous gashas no diftinguifhing tafte, and if the water beprevioufly boiled and cooled over mercury, it{hews no acidity by the moft delicate tells.Mr. Davy finds (contrary to the opinion ofHumboldt, ) that nitrous gas is not in the leaftaltered or decompofed by folution in pure water,and that it is again totally expelled by a boilingheat unaltered.

Nitrous gas is immediately fatal to animalsenclofed in it. Mr. Davy had the rafhnefs toinfpire a fmall quantity of it which gave a veryburning aftringent tafte to the mouth and throat(owing no doubt to the formation of nitrousvapour by union with the common air in thefeorgans) and the confequence was fevere inflam-mation which laded fome hours.

This gas diflblves readily in many of theacids. With the fulphuric it gives a purplebrown colour, and when in the form of nitrousvapour it caufes this acid to cryftallize. Thechange produced in the conftitution of nitricacid by the abforption of this gas has been fully-detailed under this article.

The habitudes of nitrous gas with combufliblebodies are peculiar. A taper dipped in this gasis immediately extinguifhed, but pyrophorusburns with. increafed flame, as Dr. Prieftleydifeovered. Charcoal is flowly confumed in itif kept at a red heat. The particulars of fomeof thefe experiments require a further notice, asthey lead to determine the coinpofition of the ga3»