N I T

N I T

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fames, of an exceffively pungent anil peculiar1'mell, and of the fpecihc gravity of about 1.5,or half as heavy again as water, if the nitrewas thoroughly dried before it was put into theretort, and the fulphuric acid was very concen-trated. The quantity of this acid is on an averageabout half the weight of the nitre employed.Befides this the water that receives the nitrousvnpour is converted into a weak acid liquor ofa biue-green colour.

The fubltance remaining in the retort con-cretes into a beautifully white fpongy falinemafs, confifting of fulphat of potafh with afinal 1 excefs of fulphuric acid. This may bediflolved out of the retort by hot water if theheat'has not been fo intenfe as to mejt the glafsand the fait into a kind of opake vitreous mafs.

The proportions of nitre and vitriolic acidhere given are two of the former to one of thelatter. Even a fomewhat fmaller quantity ofvitriolic acid will difengage all the acid of thenitre, but the remaining fulphat of potafh isharder, and the heat required for diftillation isgreater, fo that if it be a preferable object tolave the retort, not lefs than half the weight offulphuric acid fhould be employed. If this isincreafed to two-thirds, which is fometimesdone, the diftillation is ftill eafier, but the nitricacid contain*; fome fulphuric acid, from whichindeed it is feldorn free till further rectified.

To prepare only a few ounces of the acid, afand-heat is not necefiary, but the retort maybe heated by a lamp.

The nitrous acid thus prepared is very ftrongand fuming, and the leail drop ftains the handsyellow almoft immediately. When heated toboiling it gives out abundance of red nitrousvapour, and if kept boiling for a quarter or halfan hour (which in a narrow-mouthed fialk canbe done without much lofs of acid) it becomeswhen cold limpid and colourlefs as water, andnow no longer fumes. To preferve it colout-lefs it lhould he kept in a dark place, as thelight gradually reftores-the colour.

Thus then there are two forms or fpecics ofthis acid, viz, the orange-yellow fuming acid,and the pale limpid ; and the former is moreaccurately termed in modem chemiftry nitrousacid, and the latter nitric. The precife diffe-rence between the two will be prefently noticed;but it may be here obferved that the nitrousappears to be the nitric holding a quantity ofred nitrous vapour in folution.

Common nitrous acid contains, befides nitrousvapour, a quantity of muriatic and of fulphuricacid, the former arifing from a fniall admixture

of common fait, or more commonly of rnuriaiof potafli with the nitre; and the latter fromthe volatilization of part of the fulphuric acidadded. It is of importance often both in manu-facture and in experiment, to get rid of thefeforeign acids, which may be done in the fol-lowing way : the fulphuric acid is got rid of byrediftilling the acid upon about an eighth ortenth of pure nitre in a moderate heat, bywhich the fulphuric acid is detained-j. or elfenitrat of lead may be added to the mixed acid,which will caufe the fulphuric to feparate inthe form of an infoluble fulphat, after whichthe clear acid may be Amply decanted off, or(what is much better) fhould be rediftilled.

To feparate the muriatic acid nitrat of filvermay be dropped in gradually till all the muriaticacid falls down as muriat of filver, after whichthe clear nitrous acid may be corifidered as pure,or what is better, fhould be rediftilled.

The manufacture of this acid in the greatway is now performed with equal fimplicity inthis country and with the fame materials. Theprocefs is the following : rough nitre is firltrecryftallized, then the cryftals are put (withoutpounding) into a large glafs body, to which isadded half the weight of fulphuric acid ; a glafspipe is then luted to the body and made tocommunicate with an empty receiver, and fromthis ,by three or four more pipes with otherreceivers half full of water, but in this cafethe pipes do not dip in the water. Heat isthen applied, and the ftrong acid condenies in'the empty receiver, whilft the acid vapour uniteswith the water of the others, forming the com-mon aqua fortis. To purify the ftrong acidfrom the muriatic, the following fimple methodis found fuflicient: a fmall quantity of diftilledwater is added to feveral pounds of the acid,which caufes a great production of heat and aiudden guft of nitrous fumes, and in thefe fumesall the muriatic acid efcapes, being more volatilethan the nitric acid. By fubfequent boiling thereft of the nitrous vapour is got rid of, and theacid that remains is a nearly pure nitric acid,of about 1.5 fpecific gravity. The refiduaryfulphat of potafh is moftly fold to the alum-makers in Scotland .

The furnace and apparatus of an aqua-fortisdiftiller confift chiefly of a long iron troughfilled with fand, in which the retorts are buriedin two rows, (landing back to back, andunder which is a long brick furnace to heatthe land. Each retort has its own receiver.Sometimes inftead of glafs retorts, very thickiron pots are fubftituted with advantage. Thefe