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metal will not occupy a fpace greater than abouttwo quarts, which is but a very fcanty allow-qnpe of room for a trough for chemical pur-pofes.

In order ftill more to economize room andconfequently mercury, only one fide of thetrough is funk deep (as {hewn at a by thedotted line in the plate) being equally conveni-ent for the immerfion of a jar. The fhelf ina trough of this conftrufilion is on each fide ofthe well. It is ufeful alfo to have an iron ftemfupporting a femicircular clip, fcrewed or other-wife fattened into the' fubftance of the trougha little beyond the deep circular part of thewell, to fupport a jar when inverted and heavywith mercury. A fmall glafs tube open atboth ends and drawn out capillary at one ex-tremity, is an ufeful addition to. this apparatus,to enable the operator to fuck up and collefitthe fmall globules of mercury which will alwaysbe fcattered about during thefe experiments.

TUBE OF SAFETY.. (Fig. 66 ). See

Woulfe’s Apparatus.

WATER BATH. See Bath and Alembic.

WELTER’S TUBE, or Tube of Safety.

WORM TUB. See Distilling Appa-ratus.

WOULFE’s APPARATUS. The inven-tion of this apparatus forms almoft an sera inchemical difcovery, fo great and various is itsutility. Before it was known, the only veflelsthat chemifts employed for diftillations were,either the alembic with its refrigeratory, or theretort with its receiver. The former was de-voted almoft exclufively to the diftillation ofthofe fluids which are readily condenfed bycooling, and are not attended with the pro-duction of much permanently elaftic or diffi-cultly-condenfible vapour, fuch as water im-pregnated with the aromatic parts of vegetables,alcohol, &c. whilft the retort with its glafsreceiver, was referved for the diftillation of theftronger acids, and other fubftances accompa-nied by much uncondenfible vapour. But herea great inconvenience fubfifted, for either en-ormoufly large receivers were required, or aconfiderable number of them with double open-ings like aludels, or elfe it was neceflary toavoid the rupture of the veflels by having afmall hole, which could be opened occafionally,when the quantity of confined vapour wasjudged to be too great. But even this did notanfwer the purpofe of the chemift compleatly,for much of the vapour given out during thefediftillations, is only uncondenfible for want of

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finding water or fome other fubftance withwhich it may unite, fo that a large proportionof the products of diftillation were totallywafted. In experiments of refearch too theold apparatus was peculiarly defective, as thegafleous products, which are often by far themolt interefting, were entirely loft.

Glauber was aware of many of the defe£tsof the old apparatus, and as early as aboutthe year 1655, gave a very ingenious methodof fubftituting to the feries of perpendicularaludel-lhaped receivers, a lateral feries of plain{tone or earthen jars, each connected with theother by earthen tubes bent at right angles,and the covers of each jar having two holes,one to receive the tube bringing the vapourfrom the adjoining jar or the retort, and theother for the paflage of the tube which con-veyed the excefs of this vapour into the nextin fucceflion. This arrangement is precifelythat of the bottles of the modern Woulfe’sapparatus, but the jars which Glauber ufedwere empty, and fet in a larger veflel full ofcold water, fo as to be kept always cool. (SeeGlauberi Opera , Vol. 3. Furni Novi Philofophicifive Defcriptio Artis Dflillatorite Nova. Pars.

I-)

The great improvement made to this appa-ratus by the late Mr. Woulfe, * was to fillthefe lateral veflels with water, into which hedipped the extremity of each tube, bringinginto it the uncondenfed part of the vapour, bywhich means a vaft quantity of product is faved,which even in Glauber’s method could not beultimately detained ; fo that by having a fuffi-cient bulk of water in one or more of thefelateral veflels, no part of the produfit canefcape detention except that which cannotcondenfe, either alpne or when pafled throughany liquid. Even this too may readily be faved,by adding to the laft in the feries of bottles acurved tube, which conveys. the gas to thepneumatic trough or gazometer, where its na-ture may be examined.

Inftead of having the mouths of the lateralbottles wide enough to admit both tubes (thatis, the one which brings the vapour into thebottle, and the other which conveys the uncon-denfed part of it out of the bottle) it is a greatimprovement to have the bottles blown withtwo openings, as in g and i Fig. 59, and fome-times a third is added as in a Fig. 58, for a par-ticular purpofe which will be prefently men-tioned.

The effential parts of this apparatus thereforenf.fot 1767. ■ •

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