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Crucible? ufed for afiaying, are called Cupels.Fig. 28. & 29.

NOOTH’s APPARATUS. See Gas Satu-rating Apparatus.

OXYGEN Combufion in. A veflel very con-venient for this purpofe is fhewn in Fig. 64. c.and is deferibed under the article Gazometer.

PELICAN. PI. II. Fig. 38. This is an oldinftrument now little ul'ed, intended for longdigeftiens on a fand-bath, -or other heat, witha contrivance for eonftantly returning on thematerials at the bottom all the liquid of themenftruum which would otherwile evaporateby the heat. It is therefore a glafs alembic, in■which there are two pipes that collect the dif-tilled liquor, and again enter the lower veflel.The frnall apparatus at Fig. 37. is for the famepurpofe, and is more convenient. Its con-ftrutlion is obvious.

PNEUMATIC TROUGH. See Trough.Pneumatic.

PRECIPITATING GLASS. PI. I. Fig. 20.

This is 3. very tall jar with a narrower part attire bottom, in which any precipitate whenproduced may collect by fub'fidence, and allowof the fupernatant liquor to be decanted off withmore eafe. It is alio a very ufeful glafs inwhich to float the Hydrometer.

PROOF-BOTTLE. PI. I. Fig. 13. 14. 15.This is a glafs phial for procuring gaffes, madethin and round at bottom, fo as to bear mode-rate heat, and with a bent tube clofely groundto it for conveying the gas under any invertedveflel. It has befides fometimes another open-ing folely for introducing the materials. Thisveflel is very ufeful for experimental pur-pofes, where only moderately fmall quanti-ties of gaffes are wanted, and from materialsthat require no greater heat than a fmall fpiriflamp or candle will produce. It is an improve-ment on the original cheap apparatus of Dr.Prieftley, namely, a phial with a piece of bentglafs tube thruft through the cork and properlycemented. This latter however will oftenanfwer every end, efpecially where r.o artifi-cial heat is wanted, as in obtaining hydrogenfrom muriatic acid and zinc. It may be ufefulto mention, that corks are molt convenientlyperforated, and the hole made very fmooth andneat, by the rat-tailed file. The joining of thetube and the cork may be made quite air-tightJby fealing-wax.

PYROMETER . {Wedgwood's). See the.article Pyrometer in the former part of thisSVork.

RECEIVER, is a globc-Ihaped veflel, either

plain or tubulated, ufed in the procefs of di/fil-iation. It receives the beak of the retort, or theadopter, if this is ufed. See PI. I. Fig. 4. PI. III.Fig. 42. L PI. IV. Fig. 59. d.

RECIPIENT, Italian, is a veflel like a tea-pot, intended for the feparation of effential oilsfrom the watery liquor on which they float.

REFRIGERATORY is that part of a Dif-tilling Apparatus when the vapour is cooled andcondenfed. In the Alembic it is at the top ofthe apparatus; in the common Still it is theWorm-tub. See D filling Apparatus.

RETORT is the common and mod ufefulinftrument for Dijlillation. See PI. I. Fig. 2, 5,H. Retorts with very long narrow necks Fig . r.are made for heating thofe.fubftances which areintended to yield any of the gaffes, for here now'idth of veflel is wanted for the condenlationef vapours, and the narrownefs of the neckallows but little admixture of the external air.Retorts are made of glafs, earthen-ware, andfometimes of iron or filver. A leaden retort isufed for procuring fluoric acid.

REVERBERATORY FURNACE. SeeFurnace.

SAND-BATH. See Bath.

SERPENTINE or WORM. See Distil-ling Apparatus.

SOLAR HEAT . (Apparatus for). Averyelegant and often moll convenient method of-applying heat is by the fun’s rays through themeans of a powerful lens or mirror. It unitesthe great advantages of fimplicity and extremepower, and has been employed moft happily byDr. Prieftley and other philofophers in feveralimportant experiments. Where the fubftanceto be heated is to be at the fame time debarredfrom the accefs of the external air, the veflel mullbe thin clear glafs, that the cone of rays maybe tranfmitted through with as little lofs a*poflible. The heat produced by the moftpowerful glaffes (fuch as that of Mr. Parker)appears fully to equal, in a fmall fpace, theeffect of the blow-pipe fed with oxygen gas.

SPECIFIC GRAVITY, Apparatus for.

Though experiments on fpecific gravity donot abfcrlutely belong to chemiftry, it is necef-fary that the chemift be furnilhed with themeans of afeertaining the fpecific gravity ofboth folids and fluids with tolerable accuracy,as it aflifts much in many chemical enquiries,and the effe£I of acids, alcohol, and fome otherreagents very materially depend on their degreeof concentration which is known by their den-fity or tenuity. Therefore the feales which thechemift employs iiiould allow to be ufed hydro-