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plnte, of the combination of nitrous oxyd withpotafh, and generally of fome unfaturated potafhand carbonat of potafh. By folution in waterand cryftallization, the fulphat and fulphite ofpotafh may be feparated, thefe being much lefsfoluble in water than the other fait, but there isno means of feparating entirely the carbonat ofpotafh.

The fait of nitrous oxyd and potafh is readilyfoluble in water, has a cauftic pungent tafte,and does not part with the nitrous oxyd byboiling. But if any acid is added, a brifkeft'ervefcence takes place, and the oxyd is givenoff pure unlefs the fait contained alfo an alka-line carbonat, in which cafe the gas is mixedwith carbonic acid. Carbonic acid gas throwninto a folution of the fait expells the nitrousoxyd, fo that the affinity of the latter foralkalies is weaker than that of the weakeft acid.From a rough eftimate Mr. Davy conjecturesthat this fait confifts of about 3 parts of alkaliand 1 of nitrous oxyd by weight.

A fimilar fait may be formed with foda bythe fame methods, employing the fulphite offoda and cauftic foda, but the ready folubilicyof fulphat of foda would render it more difficultto procure the nitrous oxyd fait feparate.

The phenomena that attend the combuftionof different bodies in this gas are highly ii. tereft-tng as they afford the only means of decompo-fmg this fubflance, and of determining thenature and proportion of its conllituent parts.

Dr. Prieflley firlt obferved that when a light-ed taper was let down into a jar of this gas itburned with an increafed flame, and a cracklingnoife fimilar to the combuftion in oxygen gas,but there is this effential difference between thetwo gaffes (as far as relates to their power offupporting combuftion) which is, that when afubflance previoully ignited in any degree in theopen air is introduced into oxygen gas, thecombuftion inftantly increafes and is raifed tointenfe vehemence •, whereas, in nitrous oxydbodies previoully ignited only to a low degreeare immediately extinguifhed, and it is onlywhen already in Jlrong ignition or by the appli-cation of a firong heat to them after inclofurem this gas, that the combuftion goes on at all,and then rifes to a greater intenfity than incommon air. Thus if phofphorus is inclofedin nitrous oxyd and touched with an iron heat-6 to a low rednefs, the phofphorus melts, andmay even be fublimed unaltered, but if touchedwith an iron heated white hot, a violent deto-nation ta es place. Much caution is required

in performing this experiment. If the phofpho-rus be previoully warmed or fublimed in the gas,a violent detonation cannot be avoided whenthe heat is afterwards raifed to ignition, onaccount of the veffel being already full ofphofphoric vapour, but to make this fubflanceburn quietly and vividly in nitrous oxyd as itdoes in oxygen, it fnould be previoully fet fireto and fuddenly introduced into the nitrousoxyd.

Phofphorized hydrogen gas and nitrous oxydmixed together may be fired with the electricfpark.

Sulphur when introduced cold into the gascannot be fired by applying an iron wire evenwhite hot, and it may be fufed and fublimed inthe gas without alteration. Even when it isprevioully kindled, if only burning weakly witha faint blue flame, it is immediately extinguifh-ed in the gas. But if it is in ftrong' ignitionand then introduced in the ga» it burns vividly,with a rofe-coloured flame. In this experimentand that with phofphorus, Mr. Davy fucceededby introducing into the jar containing thenitrous oxyd, the phofphorus or fulphur in afmall tube containing oxygen, balanced fo as tofwim on the furface of the mercury withoutcommunicating with nitrous oxyd. The phof-phorus or fulphur was fired in the oxygen byan ignited iron wire, by which at the momentof combuftion the tube containing it was raifedinto the nitrous oxyd, and thus the inflamma-tion continued. The combuftion with fulphurhowever will fucceed in the following manner: hDip a flip of copper into melted fulphur; whencold fet fire to it, and when in ftrong combuf-tion introduce it into a jar containing the gas,when it will continue to burn with a beautifulrofe-coloured flame.

Iron wire, charcoal, pyrophorus, and manyother combuftible fubftances, may be burned inthe nitrous oxyd by fimilar means.

In all thefe combuftions the oxygen neceffaryto this procefs mull be furnifbed by the nitrousoxyd, confequently this gas mull either betotally decompofed, or converted into a com-pound in which the oxygen is in a lefs proportionthan before; in the former cafe the refidueafter combuftion will be mere azotic gas, (thatis, in cafe no new gas is generated by the act ofcombuftion) and in the latter it will be acompound confiderably refembling atniofphericair in conftitution. Hence too it appears pro-bable that the ftate of oxygenation of azotwhich conftitutcs atmofpheric air, is a precife

* Accuiu.