17 R I
U R I
( 457 )
The folution is acid, though more of the calculusis added than the nitric acid can diflolve ; it is ofan orange-yellow colour, which reddens by eva-poration, and produces rofe-coloured fpots onthe fkin about half an hour after it has beenapp.ied. This folution is not precipitated byany cauftic alkali, but when an excels of it isadded, an alkaline folution is produced, whichis of a rofe-colour when heated, and tinges thefkin equally with the acid folution.
Lime water decompofes the folution, andgives a white precipitate, which however is noturic acid or urat of lime, but oxalat of lime,owing to the production of fome oxalic acid bythe action of the nitric acid. This is confirmedby the more ccmpleat action of the oxymuriaticacid, f for when a lithic calculus is digefted onthis liquid, or, ftill more readily, when this acidgas is palTed through water, holding the calculusiufpended in fine powder, the colour of thelatter grows paler, it fwells, foftens, becomesgelatinous in appearance, and dilfolves almoftentirely with the gentle evolution of bubbles ofcarbonic acicl gas. The uric acid is now entirelyloft, and the folution contains muriatic acid,ammonia, and the oxalic and malic acids. Ofthefe, the two latter fubftances are entirelygenerated from the uric acid, by means of theoxymuriatic, and the ammonia is either totallyproduced by the fame means, or partially, whenthe calculus previoufiy contained a fmall portionof this alkali, which is fometimes the cafe. Butthere can be no doubt that part of the volatilealkali that appears, is actually produced in thisinftance, fince the pure uric acid will yield it byfire in cafes when none of it appears in treat-ment with the fixed alkalies.
When this calculus is boiled with the carbo-nated alkalies, little if any effect is produced,but the cauftic fixed alkalies diflolve it readily,even'in the cold, when there is an excefs of thealkali. This folution is yellow, taftes fweetifh,and alkaline, but when neutralized, the alkalineurat cryftallizes. Liquid ammonia alfo dif-folves the calculus, though with difficulty.Lime-water has the fame efteft, and the cauftictafte of the lime difappears. In all thefe cafesa true neutral fait is produced of the uric acidand the alkali or alkaline earth employed, whichis foluble in water. Thefe folutions are decom-pofed by every acid, even the carbonic, fo thatthe uric acid has an extremely weak affinity withthe feveral bafes. Thefe decompofitions tooare much affifted by the extremely fparing folu-bility of the uric acid alone, fo that as foon as
* Fourcroy.
any other acid is added to the urat, the uricacid is depofited in fmall,brilliant, bulky, needledcryftals, of a faint yellow or wood colour. TL hisis the moil convenient method of procuring thisacid for examination, namely, by digefting theuric calculi in hot cauftic potalh or foda, andthen feparating it by muriatic acid. Carbonat of ammonia will alfo feparate the uric acid fromits alkaline folutions, owing no doubt to theAmple agency of the carbonic acid which thisfait contains in fuch abundance, its ammoniabeing volatilized in the procefs.
When a portion of this calculus is heated perfe in a retort, an ammoniacal watery liquor rifes,but no oil. This is accompanied by a brownfublimate, which may be whitened by a fecondfublimation, and is then without fmell, has afouriffi tafte, is eafily foluble in boiling water,and is fomewhat different from the uric acidformed by precipitation of the alkaline folution.A good deal of carbonic acid is given out duringthe heating of the calculus, and a ftrong fetidfmell like burnt horn is perceived, together withan odour like peach-flowers, which indicatesPruffic acid.
The uric acid is contained in fmall quantityin the mod healthy urine, E for if fome of thisliquid is evaporated it depofits a fine red powder,which is foluble in alkali, and has all the pro-perties of urinary calculus. The red fedimentwhich fettles from the urine of perfons after anague fit, is of the fame nature.
The uric acid therefore, though it has manyproperties fimilar to the benzoic, and others re-fembling the fuccinic, muft at prefent be con-fidered as a diftindl acid, which occurs only inurine and in mod kinds of urinary calculi, andis diftinguifhed by its fparing folubility in water,by its feparation in a cvyftalline form from itsalkaline folution by every acid, by its folubilityin nitric acid, and the rofe-coloured tinge withwhich it ftains the fkin, by the acid fublimateand the ammonia which it gives when fublimed,and the very fmall quantity of animal oil whichis produced under the a£rion of fire.
Urat of ammonia is often found in urinarycalculi. The prefence of ammonia as an cdttEland not a produff, is afeertained by the pungentammoniacal fmell which is given out when thiscalculus is digefted with a fixed alkali. Thecalculi, of which it forms the principal part, kare generally fmall, coffee-coloured, arrangedin thin roughiflt laminae, ufually with a depofi-tion of phofphat of lime interpofed, and often in-termixed with ammoniaco-magnefian phofphat.
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TOL. II.