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A very interefting fact relating to the pro--duclion of nitrous acid from ammonia and a me-tallic oxyd was difcovered in 1789 by the Rev.Ifaac Milner, s The production of ammoniafrom nitrous acid and iron in fome circum-ftances, had been before difcovered by Dr.Prieftley, which led Mr. M. to endeavour toreverfe the experiment, and produce nitrous acidby the decompofition of ammonia by means of ametallic oxyd, when in the acft of giving outoxygen. It was made in the following manner :the middle part of a clean gun-barrel was filledwith black oxyd of manganefe, rammed in gentlyand in coarfe powder, fo as to admit the paffageof vapour through. The barrel was then madered-hot in the middle, and at one end was luteda fmall retort filled with cauftic ammonia,which was made to boil by a lamp heat, and theammoniacal vapour was thus forced throughthe red-hot manganefe. Nitrous fumes foonbegan to appear at the other and open end ofthe gun-barrel, and a confiderable quantity ofair was collected which was clearly nitrous.Owing to the impoffibility of exaCtly adaptingthe quantity of alkaline vapour to the oxygenwhich the manganefe is giving out, there willbe always found a great variety in the gafeousproduCts, but nitrous gas is always given outand generally with the ufual appearance andfmell of the red nitrous vapour when it comesin contaCt with the air. Sometimes howeverwhen much ammonia is palling through thebarrel and but little oxygen giving out, theproduCt is a mixture of nitrous gas with am-monia, and on coming in contaCt with air thenitrous gas becomes for an inftant red bychanging into nitrous vapour, after which itunites chemically with the alkali, and thereceiver is filled with white clouds of nitratedammonia.

In this interefting experiment the ammoniais refolved into its elements, azot, and hydro-gen, and the azot uniting with the oxygen ofthe manganefe forms nitrous gas or nitrousvapour, according to the degree of faturation.

Nitric acid when in vapour is decompofed bya red heat, and the produces are very pure oxy-gen gas, nitrous gas, or nitrous vapour, or ifthe decompofition be compleat, azotic gas.To give the vapour of boiling nitric acid a redheat, Dr. Prieftley adopted his own ingeniousmethod, of heating red-hot the middle of aglazed earthen tube, loofely filled alfo with

ragments of hard pottery to increafe the red-ot urface, and palling through it the boiling

vapour expelled from a quantity of pale nitricacid heated by a lamp at the other end. Inthis way the products were a large quantity ofthe pureft oxygen gas and abundance of nitrousgas, nitrous vapour, and fome undecompofedacid.

Many other feries of experiments have beenmade by Ikilful chemifts, to afcertain the exaftproportion of the conftituent parts in nitric acidand its varieties. As our limits wall not allow ■us to relate them all, we {hall conclude thispart of the fubjeCt with thofe of Mr. Davy, hwhich yield to none in accuracy, and are gene-rally allowed by chemifts to form as near ap-proximations to truth, as can be expected inthis peculiarly difficult and delicate part ofchemical analyfis.

The methods ufed to eftimate leparately theconftituents of nitric acid, have been the follow-ing : ijl. By the decompofition of pure nitreeither by heat alone or by charcoal or fome othercombuftible. But this procefs is attended withalmoft infuperable difficulties; a great varietyof products are formed in this way, all of whichwould require a feparate analyfis with an infi-nite number of precautions and neceffary cor-rections, and a portion of the acid is volatilizedwithout decompofition. idly. By the immediatecombination of oxygen and azot, in Mr. Caven-difh’s method. But this though fimpler than theformer, is nearly impracticable on account ofthe extreme laborioufnefs of the procefs and thevery fmall quantity of acid product: and ac-cordingly we find no fufficiently fatisfactoryagreement even in the careful experiments ofthe difcoverer. 3 dly. By the combination ofnitrous gas and oxygen, as in the common eu-diometrical trials, and the fubfequent abforptionof the generated acid by a given quantity ofwater. But Mr. Davy found that the refiduaryazot, which is always mixed with the pureft ni-trous gas and oxygen, in whatever way obtained,carries with it a variable quantity of nitrousacid vapour, of different compofition from theacid abforbed, and thus renders the experimentinaccurate. The method Mr. Davy adopted•was, to exhauft a glafs globe of its commonair, then to throw in a given quantity of nitrousgas, and after it oxygen gas fomewhat morethan fufficient to faturate it, then to add water toabforb the nitric acid formed (and which beforethe addition of the water renVained in the ftateof permanent vapour); then to allow commonair to enter to take the place of the condeufednitrous acid vapour; then to add ammonia t Q

* Phil. Trenf. Vol. jrj. k Refearches.

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