SUL

( 595 ) SUL

acid, will be converted, for the moll part, intofulphuric, and the cryftals are fulphur. d Henceit appears, that by the long continuance of heat,the oxygen of the liquid fulphurous acid quitsone part of its bafe in order to form fulphuricacid with the remainder. ,

Sulphurous acid combines, either direftly orby compound affinity, with the different faliti-able bales, forming a genus of falts, whichhave obtained the name of Sulphites.

For an account of fuch of the metallic ful-phites as pre known, we refer the reader tothe refpe£tive metals: there are, however, twoor three general obfervations on the i'ubjeH,for which the chemical world is indebted toBerthoilet, which may not improperly be intro-duced here. , Thofe metals that have a ftrongaffinity, both for oxygen and fulphur, fuch asiron and tin, if digelted wfith liquid fulphurousacid, furnifh themfelves with the requifite pro-portion of oxygen, by decompofing not thewater but the acid; hence there is no difen-gagement of hydrogen gas, but one portion ofthe metal decompofes part of the acid, and afterbeing thus oxydized, combines with the re-mainder of the acid and a little fulphur, whilethe reft of the fulphur produced by. the decom-pofed portion of acid, combines with the re-mainder of the metal: hence there is producedboth a fulphite and fulphuret. Zinc, on thecontrary, though in its affinity for oxygen it isequal to iron, yet being greatly inferior in itsattraftion for fulphur, decompofes the water ofthe fulphurous acid rather than the acid itfelf;hence, during its folution, hydrogen gas isgiven out, and there is no appearance of anyfulphur.

Thofe metals whofe affinity for oxygen isbut weak, as lead, mercury, and copper, arenot added on by fulphurous acid.

Some remarkable circumftances alfo occur,with regard to the adbion of metallic oxyds onthis acid: fome oxyds limply combine with theacid into a fulphite ; others, as the black oxydof manganefe, give out a portion of oxygen tothe acid, converting it totally, or in part, tofulphuric. Hence there is produced a fulphat,either mixed or not with a fulphite.

U? e onl y truft-worthy analylis of this acidwhich has yet been publifhed, is Dr. Thom-lon s s - from which it appears that 82 parts offulphuric acid, and 18 of fulphur, conftituteloo ot lulphurous acid ; according to which (ifthe analyfis of fulphuric acid by Chenevix be

* Prieftley, • Nich. Journ. Svo. vol. vi p qc

VOL. II. '

affirmed as the molt authentic) this acid con-fifts of„

68 Sulphur32 Oxygen

ICO.

The order of the affinities of fulphurous acid,as far as it has been afeertained, is the following:barytes, lime, potafh, foda, magnefia, ammo-nia, and alumine. It is feparable in the formof gas from its earthy and alkaline bafes, bythe fulphuric, muriatic, phofphoric, and tartaricacids.

Sulphurous acid, or to fpeak more correctlythe fumes of burning fulphur, is employed todifeharge the natural yellow'' tinge .from whitewoollen cloth, and to reftore filk that has grownyellow' by long wearing, to its original white-nefs. It is alfo ufed to check the fermentationof vinous liquors.

Sulphite of Potash/

The mod convenient method of preparingthis fait is- to connect a retort, charged withfulphuric acid and mercury, .with a Woulfe’sapparatus of two bottles, the former of themcontaining a little water, and the latter abouttwo-thirds filled wdth a folution of cryftallizedcarbonat of potafh, in thrice its weight ofwater. The retort being heated, fulphurousacid gas is produced, which palling throughthe water in the firft bottle, is thereby purifiedfrom any contamination of fulphuric acid, andthen enters, the alkaline folution in the nextbottle, by which it is rapidly abforbed, carbonicacid gas efcaping in bubbles at the fame time.When the effervefcence has ceafed, and thefulphurous acid is no longer taken up by theliquor, the procefs is finifhed, and the liquor,as it cools, generally depofits cryftals, if theabove proportions of alkali and water havebeen obferved.

Sulphite of potafh thus prepared, is a tranf-parentfalt, fometimes colourlefs, but often witha flight yellowiffi tinge. It cryftallizes citherin the form of lengthened rhomboidal plates ordivergent needles. To the tafte it is pungentand fulphurous; its fpecific gravity is = 1.58 :it is readily foluble in its own weight of waterat the common temperature, and in a muchfmaller quantity of boiling water. If this folu-tion is expofed to the air, it becomes coveredin a fhort time with a cryftalline pellicle ; whenthis falls to the bottom, it is fucceeded by-An de Chim. vol. xxiv. p. 254. Nich. Journ. vi. p. 94.

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