SUL

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are informed by Chaptal, that in his manufac-tory it ufed to mark between 40° and 50° onBeaume’s areometer; it was then evaporatedin leaden boilers, till it arrived at 6o° of Beaume,and was laftly condenfed in glafs retorts till itWas equal to 66 °, and was then at the commondenfity of the oil of vitriol of commerce. Weare told by the fame author, that one part offulphur affords nearly two parts of fulphuricacid at the above denfity; this however appearsto be a millake. We fhould imagine thatin the common manufactories the lofs by ful-phurous acid gas would nearly counterbalancethe increafe from the addition of oxygen and.water; indeed it is exprefsly Hated by fomeauthors that iooibs. of fulphur produce by corn-bullion an equal weight of fulphuric acid.

It has been already mentioned that the■common Englifh fulphur (and probably all thatwhich is obtained during the roafting of copperore) is unfit for the preparation of fulphuricacid, on account of a yellowifh-brown colourthat it gives to this fluid, and which it is ex-tremely difficult to get rid of. For this reafonthe refined Sicilian fulphur is the only kindthat is employed in this manufacture, at leaftin Britain . But though by the due felcftion offulphur one fource of impurity is avoided, yetthere are others which, according to the ufualmode of preparing this acid, it is impoflible toefcape. The watery acid as it runs from theleaden chamber, is neceffarily mixed with ful-phat of lead, with a frnall quantity of nitrousacid, and holds fufpended in a minutely dividedftate a portion of fulphur, from which it ac-quires a yellowifh colour: during the evapo-ration in the leaden boilers, probably a listlemore fulphat of lead is taken up. The highheat required for the final concentration of theacid in the glafs retorts, by caufing the nitrousand part of the fulphuric acid to re-aft on thediffufed fulphur and other inflammable impu-rities, takes away, for the molt part, the colourfrom the fluid, and drives off the whole of thenitrous gas and fulphurous acid, together witha portion of water: thus the only impurity thatfinally remains in the fulphuric acid is fulphatof lead. But it not unfrequently happens thatthe acid during concentration lofes its colourvery flowiy, to expedite which it is ufual toadd a little nitre, the acid of which being fet atliberty afts rapidly on the colouring matter anddeftroys it, being itfelf finally driven off in theftate of nitrous gas.. The alkaline bafe of thenitre however remains diflolved and combinedwith the fulphuric acid, fo that befides fulphatof lead it is further contaminated by fulphat of

potafh, and if the nitre is added fomewhat inexcefs, and only a little while before the con-centration is finifhed, it is very probable that aportion of nitrous acid will ilill remain. Noris it of trifling moment that the whole of thenitrous acid fliould be expelled, for if the dyeror callico printer employs an impure acid ofthis defeription in making Saxon blue (fulphatof indigo) he will find to his coft that he hasgot a green inftead of a blue pigment. Fromthe occafional occurrence of the above and otherfimilar difappointments it is that the dyers onthe continent, when they can procure citherthe fulphuric or the genuine vitriolic acid, al-ways prefer the latter, notwithftanding thegreat fuperiority of its price.

Common fulphuric acid may be freed fromthe fulphats of lead and potafh which it gene-rally contains, by diftillation; this, however,though apparently a very Ample procefs, israther a nice matter to manage, according tothe ufual method. Sulphuric acid is not capableof being diftilled at lefs than a red heat, whentherefore the denfe hot vapour firft comes incontaft with the necks of the retort and receiver,it is apt to break them, unlefs the precautionhas been taken of thoroughly heating them bymeans of a pan of charcoal placed beneath, aminute or two before the diftillation commences.All this rifle however may be avoided (and infome laboratories it aftually is fo) by connectingthe glafs body, in which the acid is boiled, withthe receiver, by means of a tube of platina :boiling fulphuric acid has not the leaft aftionon this metal, and the vapour in its paflagethrough becomes fo far cooled and condenfed,that it flows into the receiver in drops.

Sulphuric Acid , when pure, is perfeftlytranfparent and colourlefs; but the commonoil of vitriol of the (hops has almoft alwaysa very pale hair brown tinge, probably arifingfrom the carbonization of a little of the cementwith which the bottles in which it is kept areclofed. In its general appearance and confif-tence when fliaken it is not unlike oil, whenceit derived its commercial name ail of vitriol.It is entirely inodorous : to the touch it is atfirft fmooth and unftuous, but’it prefently afterexcites a violently burning fenfation,and corrodesthe flein with great rapidity ; even when largelydiluted with water, it is acerb and intenfelyfour, and fets the teeth on edge. It changesmoft vegetable blues to red, and exhibits theother generic characters of acids in an eminentdegree. Concerning the utmoft poffible denfityof this acid in an uncombined ftate, there is a3 A 2