SUL

SUL

( SSI )

ous acid appears incapable of decompofing it,but ail the other acids throw down from it aquantity of fu phur. The fixed alkalies, whendry, produce with it a violent efrbrvefcence, anda considerable degree of heat. If ammoniacalgas is thrown into it, the vefiel is foon filledwith a purple vapour, and the liquor becomesi'clio, and of a deep red colour; but whenn.ixed with water it fpeedily diffolves, and lul-p. ur is precipitated. This fingutar fubftancehas not yet been very exadtiy analyzed ; indeedit appears tu be by no means uniform in itscompofmou : in one l'pecimen Dr. Thomfonfound the relative proportions of muriatic acidand oxyd of lulphur to be as 44. of the latter to2 . of the former. In another'fpecimen theproportions were 47.1 muriatic acid, 35.2oxyd of fulpbur, and 4. fulphuric acid. Theoxyd of fulpbur .appears to be compofed of93.8 fulpbur, and 6.2 oxygen.

' SULPHUROUS ACID. Aduk Su/ureux.Fr. Scktvefeiigte Saure , Germ.

The fuffocating vapour that rifes during thecombuftion of i'uiphur, is fulpbur jus acid,and although fome of its moll obvious proper-ties muft have been known from time immemo-rial, yet the firft chemift who appears to haveexamined it with any attention was Stahl. Thiseminent philofopher named it phlogijHcatcd v tri-clic add, becaule he ..onfidered it as differingfrom common vitriolic acid only in containinga larger proportion of phlogifton or the princi-ple of inflammability : he alfo {hewed that itmight be combined with potafh, by dipping acloth in a folution of this alkali, and expofingit, while yet moift, to the vapour of burningfulpbur. Scheele made fome additions to ourknowledge of this fubltance, which was ftillfurther extended by the important difeoveriesof Dr. Prieitley. Next, Bertholiet inveftigatedthe properties of this acid and its falts, with Lisaccuftomed fagacity. The accuracy of Vauque-lin, in conjunction with Fourcroy, enlargeditiil further our acquaintance with this fi1b-ltance; and, finally, we are indebted to Dr.Thomfcn, for the beft analyfis of it that has yetbeen pubiifhed, and for the difeovery of fomemterefting lacits, which had been overlooked crobfeurely Hated by preceding inquirers.

There are two ways of procuring fiilphurousacid ; namely, by the combuftion of fulpbur, orby the partial decompofition of fulphuric acid,'lhe firft of tl efe methods, although apparentlyvery fimplc, is in fa& the mod troublefome ;for if the combuftion is performed by atmof-pheric air, the newly-formed acid mixes with

the residual azotic gas, from which it is incapa-ble of being diredtly feparated. If, on-the otherhand, oxygen, gas is made.ufe of, not only ful-phurous but fulphuric acid is produced, andpart of the oxygen remains mixed with the ful-,phurous acid gas. Hence it is that, for chemi-cal experiment, this acid has always been pro-cured by the decompofition of fulphuric acid.

Various fubftances have been employed forthis purpofe, fuch as woed, charcoal, oil, alco-hol, and other vegetable fubftances and pro-ducts : all rfiefe, however, are more or lefsobjectionable, as both carbonic acid and gafle-ous oxyd of carbon are given out together withthe fulphurous acid. Sulphur itfelf has beenmade ufe of, and the only objection is the flow-nefs with which the acid is thus produced.Dr. Prieftley firft employed the metals-, infteadof the more compound combuftibles. He foundthat iron and zinc, being metals fo greedy ofoxygen as to decompose water, were by nomeans fo proper for tlrs purpofe as copper,filver, ormercuTy; fmee in the former cafe theacid was mixed more or lefs with hydrogen,.proceeding, no doubt, front the decompofitionof the water which common fulphuric acidcontains.

Sulphurous acid gas is thus prepared : pourinto a narrow necked glafs retort two p -rts, byweight, of concentrated fulphuric acid, and onecf mercury ; dip the beak of the retort undermercury, and then apply a lamp or a pan ofcharcoal : when the acid gets warm, it willbegin to adt on the mercury, and bubbles ofgas wid be difengaged : as foon as the commonair of the vefiel is driven’out, and is fucceededby bubbles of white fuffocating vapour, an in-verted jar, filled with mercury, may be placedover the bc-al; of the retort, and will thus befpcedily filled with gas. This gas is fulphurousacid in its pure ft ftate, and exhibits the follow-ing properties. It is invifible, colourlefs, andelallic, like common air; it lias an extremely,pungent fuffocating odour, and is incapable offupporting either combuftion or animal life.Its ipecific gravity is about o 0025, or fome-what more than twice as great as that of at-mofpheric air It is acerb and four to the tafte,reddens moft blue vegetable juices, and, aftera time, deftroys the colour of many of them..It does net appear fuiceptible of any change bymere heat; but, according to an experiment byMcnge and C ouet, if expofed at the fame timeto great prendre and a c.-id equal to 3i°Fahr.it lofes its elafticity, and ; flumes a liquid ftate.Water, by Ample expofure to an atir.oiphere of.