NIT

N I T

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«n nitrous acid, we proceed to mention othersby which it has been attempted to afcertain theexaCt proportion of the conftituent parts of nitricacid and its feveral modifications.

Chemiftry is indebted to Mr. Cavendifli forthe important difcovery of the true nature ofnitric acid; this eminent philofopher havingcompofed the acid by pafling the eleCtric fparkfor a vaft number of times through a mixtureof azotic and oxygen gaffes, and thus demon-ftrated that azot is its radical or bafis. c

The apparatus employed in thefe intereftingexperiments confifted of a glafs tube bent inthe form of the letter V, which after being filledfvith quickfilver, was inverted into two gladesof the fame fluid. The air to be tried wasthen introduced into one of the legs of the tube,and in the other were thrown up teft liquors, orother fluids as required. A communicationwas then made with a powerful electric ma-chine, fo as to take fparks fuccelfively throughthe air in the tube. Common air alone wasfirft tried (which confifts of about 77 per cent.of azot and 23 of oxygen) and litmus liquorwas introduced in contact with it up the otherleg of the tube. On palling the fpark throughif repeatedly the litmus liquor acquired a redcolour, and the air was diminifhed. Whenlime-water was introduced inftead of the litmus,not the leaft turbidnefs was perceived, thoughthe air went on diminifhing to two-thirds of itsoriginal bulk. A mixture of azotic and oxygengaffes was then tried, and the lime-water asbefore remained clear, but on adding ammoniaa brown fediment appeared.- This confifted ofearbonat of lime mixed with a little mercury,which the eleCtric fpark had oxydated, andhence both the lime and the mercury mull havebeen diffolved in the water of the lime-water,by fome acid, which acid, was afterwards provedto be the nitric.

Mr. Cavendifh afterwards found that theproduction of nitric acid from thefe two airs,was much haftened by electrizing them incontafl: with a fubftance for which the acidwhen formed has a great affinity, and accord-ingly foap-lees or. cauftic potafli was ufed.

One leg of the tube being filled with a mixtureof azot and oxygen, and the other with thealkaline folution, fparks were taken through theair for a great number of times, after whichthe alkaline liquor was found compleatly fatu-rated with acid, and on being evaporated todrvnefs a fmall quantity of a fait was left, whichwas evidently nitre. In feveral experiments* l’hil, Trans. Vol. lxxv. and lxxviii.

however when the electrization was continuedfo long that the acid produced was more thanfufficient to faturate the alkali, the excefs ofacid diffolved a little of the mercury bywhich it was confined, and nitrat of mercurywas alfo found mixed with the nitrat of potalh.The particular tells by which the prefence ofnitrat of potalh and nitrat of mercury weredeteded need not be here related; it is fuffi-cient to obferve that they were perfectly fatis-faCtory .

From thefe molt valuable and fundamentalexperiments it is proved, that nitric acid confiftsof azot of oxygen in certain proportions, andthat the eleCtric fpark is capable of making themunite in that form and proportion which isneceffary to conftitute this acid, whatever bethe aCtual proportions of thefe gaffes in contaCtwith the eleCtric fpark. Hence too we findthat nitric acid is always generated wheneverthe eleCtric fpark is taken in the open air.

The procefs as given by Mr. Cavendifh isextremely laborious, and requires great pesfeve-rancc, as even with a powerful machine, andcontinuing the electrization for feveral days,only a very few grains of nitre are produced inthe potafli folution.

Mr. Henry f has given the following veryaccurate directions for performing this experi-ment : let a ftraight tube prepared for eleCtricalpurpofes, be filled with and inverted over mer-cury. Pafs into it a portion- of common air,or, in preference, a mixture of azotic gas withtwice its weight of oxygen. Let an iron wirelengthened out with one of platina, be intro-duced within the tube, fo that only the lattermetal may be in contaCt with the mixed gaffes,and let the end of this wire be diftant \ of aninch from the extremity of the upper one.Then pafs a feries of eleCtric Ihocks throughthe gaffes for feveral hours. The mixture willgradually leffen in bulk, will redden litmusintroduced within it, will give the fmell ofnitrous acid, and will neutralize a few drops-of potafli, and produce nitre.

On account however of the difficulty of pro-curing any tolerable quantity of nitric acid inthis way, the proportion of its ingredients can-not be inferred with much accuracy. Mr, 1Cavendifli did not find any very fatisfaCtoryagreement in the aCtual quantities of the gaffesabforbed in the different experiments, but onthe whole it appears from them, that fomewbatmore than twice as much pure oxygen as azotconftitutes nitric acid.

' Epitonie.ofChcm.^thEiii,