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of acid and production of oxygen gas, whereno room is afforded for the efcape of oxygen inits proper gafeous form, its production muff beprevented. But on the other hand the narrow-er the vacant confined fpace is, above the acid,the more fpeedily will it become faturated withnitrous gas, owing to the conftantly accumu-lating preflure of the oxygen gas above it.

The effeCt of heat on nitric acid alreadyfaturated with nitrous gas, or in the colouredfuming ftate, and unconfined, is fimply to ex-pell the nitrous gas, and a portion of the acid inthe form of nitrous vopour, and thus to leavethe acid pure and colourlel's.

The more concentrated the acid is the great-er is the quantity of nitrous gas which it willabforb, and at the fame time the eafier willit again give out the gas when heated.

It may appear contradictory to experiencethat nitrous gas, which in its natural ftate is fogreedy of oxygen and unites with it fo readily,fhould appear to mix with it in combinationwith vaporized nitric acid without contractingany union with it. It is by no means impro-bable however that this is only during theapplication of heat, which is conftantly obferv-ed to counteract the chemical union of gafeousbodies, and befides, the prefence of the acidvapour may operate in preventing this union,for it does not neceffarily follow that theaffinities of nitrous gas faturated with acidvapour fhould be the fame as fimple nitrous gas.

The union of nitrous gas with nitric acid bothdiminifhes its fpecific gravity and gives it aprodigious tendency to volatilization, and aswill appear from fome experiments which willbe prefently mentioned, this acid may be totallydiffipated in red nitrous fumes when the quan-tity of nitrous gas or vapour is exceflive.

The compofition of nitrous vapour is certain-ly various, and it may exift with an excefs eitherof oxygen or of azot according to the way inwhich it is procured, and by this Berthollet explains feveral apparent contradictions in itsphenomena.

The analyfis of nitrous vapour is extremelydifficult, owing to the impoflibility of confiningit unaltered in jars by any known fluid, as ita£ts powerfully on almoft every fluid in nature.l)r. Prieftley made many attempts to procure it111 quantities and tolerably uniform in its com-pofition. He found it produced readily by therapid folution of bifmuth in nitric acid, but themc y?2. c * on the m hole the moft convenient wasto di olve lead in dilute nitric acid, and evapo-rate the folution to compleat drynefs. This

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left a white nltvat of lead, which when put mtoa fmall glafs tube or retort and heated ftronglygave a large quantity of red nitrous vapour inconfiderable purity. This fpecies of nitrousvapour however feems to difter from that pro-duced by the fuper-faturation of nitrous gaswith oxygen confined by mercury, and from thatproduced by heat from nitric acid, for thisfrom the nitrat of lead abforbs oxygen from theair in the fame way as common nitrous gasonly not fo rapidly. It is with this nitrousvapour that Dr. Prieftley made many experi-ments on its abforption by different bodies,fome of which are as follows:

Water impregnated with this vapour wasincreafed one third in bulk, and in this ftatewhen left at reft was conftantly again exhalingthe vapour with great force fo that it couldwith difficulty be kept in clofe-ftopped phials.The colour was bluilh green. On pouring alittle into a glafs and blowing away from thefurface the red vapour iffuing out, the colourof the liquor gradually changed to pale yellow-like common nitrous acid, and it was in everyrefpedt fimilar to this acid. The acid made inthis way is alfo purer than the common fpiritof nitre, as it contains no admixture of muriaticacid.

Oils abforb this vapour readily and in gene-ral are ftiffened and coagulated, as wiil befurther mentioned under the article Oz7.

Sulphuric acid abforbs nitrous vapour. Onputting a little of the acid into a phial full ofthe vapour and fhaking it for a time, the redcolour of the air difappeared and a vacuum wasformed above the acid, which laft became of alight blue colour exhaling a white vapour. Onputting fome of this acid into a glafs and gentlypouring water on it no change was obfervedat firft, but on ftirring the mixture great heatwas excited, and a vaft quantity of red vapourwas expelled with vehemence. The acid afterthis feemed to have loft all that it had before,abforbed and to be merely fulphufie acid dilutedwith water. When concentrated acid is fullyfaturated with nitrous vapour and fuffered toremain at reft for a time it cryftallizes, as willbe further mentioned under the article Sulphuric add. % ■

The muriatic acid alfo abforbs the nitrousvapour and in confequence affumes a deeporange colour, but without much increafe ofbulk, and is converted into a very powerfulnitro-muriatic add or aqua regia. .

Having thus given a fliort abftradt of fomeof Dr. Pridtley’s moft important experimentsT