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The acetic acid diffolves the true refins evenwithout heat when digefted with them for aconfiderable time, and on the addition of waterthe whole is again feparated, apparently un-changed. This latter method is ufeful in ana-lyfis to feparate refin and gluten, both of whichare foluble in acetic acid, but the latter remainsin folution when water is added. As the aceticacid does not (like the fulphuric and nitric)alter the refin, it affords a very ufeful re-agentin chemical analyfis.

A very fhrong refemblance exifts betweentire refins and the effential oils in many of theirmoll important properties, whence fome che-mifts have been difpofed to confider thefe oilsas the origin of refins. When an effential oilis expofed to the air, much of it is entirelyevaporated, but the portion which is left gra-dually thickens, water appears on the furface,and the oil lofes its volatility, and with it muchof its fmell, and gradually approaches to theHate of refin. This change has already beenmentioned under the article Oil Effential (page183) and alfo the method of reftoring a part ofthis oil by means of fulphuric ether into itsoriginal ftate, and the perfect refinification ofthe remainder.

Nitric acid alfo converts the effential oilsinto a refin, where the mutual action of the twofubftances (which is very rapid and intenfe) ismoderated by dilution, or very gradual affufionof the acid in fmall quantities. This change(which is alfo mentioned in the fame article,p. 184) takes place very remarkably with oil ofamber, which refembles the effential oils in manyproperties. If about its own bulk of fumingnitrous acid is poured on it gradually, muchheat is excited, and nitrous gas is given out,though the action is altogether lefs than withthe effential oils, and in fome hours the wholeis refolved into a yellow acid liquor, weak ofacid compared to the quantity employed, onwhich fwims a tough yellow refin intenfely bit-ter, aromatic, infoluble in water, but which dif-folves in alcohol, and is precipitated from it bywater. This fingular fubftance leaves a rnulkyfmell when a little of its folution is fuffered todry in the air, and it has been introduced intomedicine under the name of Artificial Musi.

We may conclude this article by a flrortenumeration of the molt important of the truerefins, the gum refins, and the fubftances, notprepared by art, to which a refinous nature hasbeen ufually attributed. “ To attempt to enu-merate them all would be endlefs, as there are

• Murray Apparatus Vedicanv

few plants from which a fpecies of refin maynot be extracted by art, and even the number ofthofe that exfude fpontaneoufly is extremelygreat.

Though no claffification will correftly cor-refpond with their chemical properties, the li-mits between the refins and gum-refins not be-ing very precife, we may ufefully arrange thegreater part of thefe fubftances under the headof Liquid Refins or Balfams, Solid Refins, andGum Refins. The two firft claffes are entirelyor almoft entirely infoluble in water, exceptthey contain benzoic acid, but totaliy yield toalcohol. Diftillation with water extracts fromthe liquid refins a large quantity of effential oil,and leaves a refidue much refembling the folidrefins. The gum-refins are partly foluble in ■water and partly in alcohol.

Liquid Resins.

1. Turpentines . Under this name we mayinclude all the liquid refins exfuding from thedifferent fpecies of pine, which from their im-portance in the arts and the immenfe confump-tion of them will be feparately deferibed underthe article Turpentine . They all yield abund-ance of the limpid effential oil of turpentinewhen diftilled, and by different modes of pre-paration furnifh feveral varieties of rofin, pitch,tar, See. There are at leaf! four fpecies ofturpentines commonly known in the fhops, theOhio, Venice, and Common Turpentine , and theCanada Balfam.

2 . Balfam of Capivi or Copaiba is a clear yel-lowifli refinous juice, about the confiftence ofthin treacle, which flows in confiderable quan-tity from incifions made in the bark of a largetree of South America , the Copaifera Officinalis.

This balfam has a very agreeable fmell and apungent bitterifh tafle. It grows differ by longkeeping but never concretes into a folid. Itdiffolves totally in alcohol. When diftilled withwater it yields nearly half its weight of effentialoil, and a brittle inodorous refin is left. It ap-pears therefore to be a natural combination,Amply of refin and effential oil.

3. Balfam of Mecca , Opobalfam, or Balfamof Gilead. This is a liquid refin which exfudesfrom the Amyris Opcbalfamiitn, a fmall evergreentree that grows in many parts of the Levant,and alfo in great perfection on the fhores ofthe Red Sea . It bears an extremely high priceamong the Turks, who employ it chiefly as acofmetic, and it is fcarcely ever found genuinein any other part of Europe .

It is moderately fluid, of a yellowifh white

Lewi! Materia Med. &c, &c.