OIL

OIL

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fourth day fmall particles of yellow oil will befeen floating on the furface of tile water, whichin the courl'e of a week will have increafed to athin fcum: this is taken up by a little cottontied to the end of a flick, and fqueezed into afmall vial.

r lhe oil contained in the fragrant blofloms ofthofe plants which have none in their otherparts, as the violet, the mignonette, the jaf-mine, the tuberofe, the hyacinth, and all thefcented liliaceous plants, &c. although exceed-ingly odorous, is fo minute in quantity and foeafily deftroyed by heat as to be incapable ofbeing extracted in any other way than by meansof the oil of ben, as deferibed in the laft article.The fragrant oil may afterwards be feparatedfrom the oil of ben in the following manner.Let a vial be half filled with a mixture ofalcohol and perfumed oil in equal proportions,and fhaken for a few minutes that every particleof each may come in contact with the other:then pour off the alcohol from the oil, whichwill be found to be nearly inodorous, havingyielded its eflential oil to the alcohol. Let thisperfumed fpirit be fhaken again with fucceffiveportions of oil, till the richnefs of its fragranceis not fenfibly increafed, and then pour it intoa bafon containing two or three times its bulkof pure water: the water and alcohol willcombine together, and the greater part of theeflential oil will be liberated and will float atthe top of the liquor, from which it may befeummed off by means of a little cotton. Theliquor being afterwards fubmitted to very gentlediflillation, the firft portion of fpirit that comesover will be found to be ftill very fragrant, andmay be employed, mixed with frelh alcohol, intreating other portions of fcented oil.

By far the greater number however of eflen-tial oils are obtained by dire£t diflillation. Ifthe fubftance to be treated is a frelh herbaceousplant it requires no previous treatment, but if itis a dried plant, a few hours maceration inwater is advifable; if a bark or wood is to bediftilled it muft be rafped or cut into fhavingsand macerated for feveral days. This beingdone, a tinned copper ftill or alembic is tobe charged with the folid materials clofelyrammed down, on which is to be poured juftwater enough to cover them, the head beingthen luted on and the refrigeratory filled withcold water, the fire muft be lighted and foregulated as to keep the contents of the ftillconftantlj fimmering, but fcarcely boiling. Thefleam being condenled in the worm will form» fmall ftre.am of water, and is to be collected

in proper veffels till it comes off nearly infipidand inodorous, when the diflillation is to beflopped. The firft part of the produce beingturbid from fuperfaturation with eflential oil isto be kept for fome hours in a cold place, duringwhich time the excefs of oil will feparate fromthe water, and either float on its furface or finkto the bottom, according to its fpecific gravity.The compleat reparation of the oil from thediftilled water is effected by a very fimple in-flrument called the Italian recipient, (deferibedin the appendix) and the whole of the waterdrawn oft' in the firft diflillation is to be em-ployed as far as it will go in the next, infteadof plain water, by which it is manifeft that theproduce of oil in the fecond diflillation willexceed that of the firft, (other circumflancesbeing equal) by all the quantity held in perma-nent folution by the water of the former procefs.Hence it is manifeft that by this mode ofproceeding, the amount of oil yielded by equalquantities of the fame fubftance will form aconflantly increafing feries, till the whole of thewater drawn off by each diflillation is compleat-ly faturated with oil. This accounts in fomedegree for the great difference in the propor-tions of oil obtained by different chemifts fromthe fame plants; for as Bindheim has fatisfac-torily fhown, it is not till the feventh, or evenin fome cafes the tenth diflillation that theproduce of oil attains its maximum.

It is not only from the odorous vegetablesthemfelves that eflential oil may be procured,but alfo from fucb of the immediate productsof vegetation as poffefs any odour ; fuch are thebalfams and many of the refins and gum refins.The procefs to be followed is diflillation withwater and precifely the fame fubfequent treat-ment as we have already deferibed.

The peculiar odour of vegetables, when notin a (late of decompofition, depending on thevolatile oil that they contain, it will be obviousthat the odours of the oils themfelves mull beequally various and therefore incapable of beingdeferibed. The tafte of all of them is exceed-ingly hot and pungent, but in fome, particularlythe oil of peppermint, is followed by a remark-able fenfation of coldnefs: this however ismerely a nervous fenfation, the thermometricaltemperature undergoing no change, _ The acri-mony of fome of the oils, as the oil ,of cloves,is fo great as a£tually to deftroy the outer fkinof the tongue and of other fenfible parts. Theconfiflence of the eflential oils is very varioys :fome being as limpid as water, while others arethick and glutinous like the exprefled oils. A