TIN

TIN

( 451 )

of its oxygen—excites no deflagration withnitre—is infoluble in dilute nitric acid—and isnot readily reduced to the metallic ftate. Thereare befides feveral other important differencesbetween die faks and compounds of thefe twooxyds, as will be feen further.

Sulphuric acid diluted with about a fourthpart of water, will diffolve about a quarter ofits weight of tin, when this metal is added infinal! grains or filings, and the foiution afliitedby a moderate heat. An effervefcence of ful-phurous acid vapour arifes, and i'ometimes ful-phur in fubftance is produced e from the totaldeconfpofition of part of the acid, which fwimson the furface of the foiution when hot, butfubfides on cooling. The colour of this fulphatof tin is yellowifh brown, which becomes clearon {landing. When faturated it depofits, afterawhile, needled cryftals of fulphat of tin. Ifthe foiution is evaporated almofl to drynefs, itbecomes on cooling a white femi-opake rnafs,which is moftly again foluble in water. Whenfulphat of tin has been long boiled, a copiouswhite precipitate fubfides which will not againdiffolve, and conlifts of the perfebt oxyd oftin retaining a fmall portion of the acid, and istherefore a fub-fulphat. The fupernatant liquoron copious dilution with water yields a furtherquantity of a fimilar white precipitate, afterwhich fcarcely any of the metallic fait remainsin the foiution. A fimilar pr-ecipitaie takesplace in a greater length of time by fimple ex-pofure of the foiution of the fulphat to the air. Itis probable therefore that the only permanentlyfoluble ftate of union between fulphuric acid andtin is when the metal is at an inferior degree ofoxydation, and that thefe precipitations are oc-cafioned chiefly by an increafe of oxydation ofthe metallic fait, which is alfo analogous to thehabitudes of the other falts of this metal. Thefulphuric acid when much diluted has no fenfi-ble adtion on tin, but it would probably diffolveits fub-oxyd.

The adlion of nitric acid upon tin is ex-tremely curious. When this acid, highly con-centrated, is poured upon tin filings, no actionwhatever enfues, but on dilution with a littlewater a moil violent effervefcence immediatelyfollows, more violent than with any other me-tal, a prodigious eruption of nitrous gas takesplace, and the metal is fpeedily reduced to abulky white powder, which is the perfedt oxyd©f tin retaining a fmall portion of the acid.

When the adtion of the acid is over, and themixture has been diluted with water, and al-lowed to clear by fubfidence, the fupernatantliquor is moderately acidulous, but containsfcarcely a particle of metal in foiution, fo thatit may be faturated with an alkali with verylittle change of its tranfparency'; but on evapor-ation nearly to drynefs it depofits in the formof a white oxyd what little of the metal it {tillretained. Tin may however be diflolvcd in ni-tric acid,, if it be confiderably diluted, withoutexciring any effervefcence. In this ftate, when'the metal is immerled in the acid it graduallyfalls to pieces in the form of a black powder/which is quietly difl'olved in the acid till thewhole difappears,. or till the acid is faturated.-Some heat is given out in the procefs, whichflieu'd be checked by putting the vefiel in coldwater ; and to make a fiiturated foiution, thetin fnould only be added in fmall quantity at atime.

This foiution is yellow, and in a day cr twoit depofits fpontaneoufly part of its metal in theform of an oxyd, or immediately, if at allheated. Both the foiution and the oxyd how-ever contain the metal in the lower ftate ofoxydation, for both the former, and the latter,when rediffolved in muriatic acid, precipitatecorrofive muriat of mercury black. If nitricacid is added to the foiution, and heat applied,a copious effervefcence arifes, and the whole ofthe tin feparates as white or perfect oxyd.The union between nitric acid and oxyd of tintherefore is verv weak and-little permanent, andonly exifts when the metal is in the ftate offub-oxyd.

Whenever tin is difl’olved or oxydated by ni-tric acid ammonia is generated, and in veryfenfible quantity. The produbtion of this alkaliis rendered very apparent in the following way..Moiften a few drachms of tin filings with nitricacid fomewhat diluted, and in the midft of theeffervefcence excited thereby add a quantity ofquicklime in powder, when on rubbing themtogether a very pungent fmell of volatile alkaliwill be perceived. In this cafe the ammoniawhich is formed, firft unites with part of the ni-tric acid, but is again expelled from it by the lime, .and being volatilized is made obvious to thefmell. The production of ammonia implies a verycomplicated abtion. As this alkali is not con-tained, as fuch, in the nitric acid, the water, orthe tin, it mult be produced by the inftantaneouscombination of its elements, azot and hydrogen,during the mutual adtion of.thefe three bodies.

’ Bsufne. 1 Proult J. J’hyf- tom. 51.

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