SUL

SUL

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properly roafted; that part of the fulphurwhich efcapes combuftion rifes in vapour, and.collects in the dome (the door of which is onlyopened to admit frelh charges of ore) whenceit pafies through the hue into the chamber,where it preiently concretes, lining the Tides and roof; each chamber has a door by meansof which, about once in fix weeks, it is clearedof the fulphur. This rough iulphur is infpungy pulverulent crufts, of a dirty greyifliyellow colour. For its purification it is meltedin a boiler, the impurities are got rid of byfcumming and fubfidence, and the fluid mafs isthen laded into cylindrical moulds to form thecommon roll fulphur or brimftone, or intocones about two feet high forming the loaves offulphur. The impure dregs are alfo fold inthe ihops under the name of fulphur vivum.

Befides the common fulphur there are twoother forms in which this fubftance appears incommerce, namely, the fublimed, or flowers offulphur ; and the precipitated, or magflery effulphur.

Flowers of fulphur are prepared in the labo-ratory, by heating in a fand-bath an earthen cu-curbit charged with roll fulphur, and fur-mounted by a fet of aludels; at a gentle heatthe fulphur firft melts, then rifes in vapour, andconcretes within the aludels in the form of aglittering yellow powder, which when exa-mined by a microfcope appears to be compofedof minute cryftals. Flowers of fulphur aremade in the large way by conducing the va-pour of melted fulphur into clofe chambers in-lfead of aludels, and being prepared with lefscare it is often inferior in purity to that ob-tained by the former method. Flowers of ful-phur, however prepared, are more or lefs acid-ulous from a mixture of fulphureous acid, onwhich account an infufion of them in water,reddens tinfture of litmus; this acid, however,may eafily be got rid of by walhing the powderfirft with a warm and very dilute folution ofpearl-afh, and then with two or three fucceffiveparcels of warm water.

Magiftery of fulphur is prepared by decom-pofing by the fulphuric or any other acid afolution of alkaline fulphuret; a copious whiteprecipitate falls down, which is to be thoroughlyedulcorated with fucceflive portions of warmwatei. Sulphur in this ftate has a dull earthyappearance, owing to its extremely minute ftateof divifion ; it is of a yellowilh white colour, isfmooth and almoft unftuous to the touch; byexpofure to light it acquires a yellow colour.It is generally looked upon as the pureft form

'•VOL. II.

of fulphur, yet from fome of its properties andthe mode in which it is prepared, there is fomereafon for fufpecting that a portion of hydrogenenters into its competition.

The fulphur that is procured in the roaftingof ores, efpecially thofe of copper, is apt tocontain befides earthy impurities a very notableproportion of arfcnic, while on the other handthe volcanic fulphur in general, and that ofSicily in particular, is entirely free from thiscontamination. This is the caufe of the uni-verfal preference given by the manufafturers offulphuric acid to Sicilian, over Englilh fulphur;and hence it is a matter of fome confequenceto be able to afeertain in a compendious andfatisfadlory manner the purity of any particularfample of this fubftance. The following me-thod will, we believe, be found to anfwer everypractical purpofe. Having rubbed to fine pow-der in an earthen-ware mortar fome of the ful-phur to be examined, take ioo grs. and put itinto a Florence flalk with 5 oz. meafures ofthe befl oil of turpentine; heat the mixturegently over a lamp, or a pan of charcoal, till ithas boiled for about a minute, then pour theclear hot folution into a fix or eight-ounce vial,flop it with a cork, and fhake it till the liquorhas cooled down to the temperature of thehand ; it will now be quite turbid with fulphurthat has feparated from the oil during its cool-ing, and being run through a glafs funnel verylightly plugged with fine tow will pafs outclear, leaving the fulphur behind. The oil isnow to be again transferred to the fulphur re-maining in the flalk, and to be a fecond timeboiled, cooled and filtered as before. By re-peating this ptocefs four or five times, therewill be left only a brownifh orange refid ue, onwhich the oil will refufe to aft any longer.This refidue being laid on a piece of earthenware is to be expofed to a heat not higher thanthat of melting lead, till it ceafes to exhale anyfulphureous vapours; being then rubbed upwith a little moiftened charcoal, and prefledinto the bowl of a tobacco-pipe or any otherconvenient veflel, it is to be heated nearly red,upon which a white vapour will arife, and Ihowitfelf to be arfenic by its peculiar garlic odour.The fulphur precipitated from the oil of tur-pentine may be entirely freed from this latterby expofure to the air and light for a day ortwo; it will then be of a beautiful fparklingyellow colour (far fuperior to that of the com-mon flowers of fulphur) and entirely inodorous.The common Englilh brimftone or roll fulphurfometimes contains a full X V of infoluble reft-2 Y