O I L
OIL
( 178 )
mixture, which lathers like an infufion of com-mon foap. The watery folution exhibits thefollowing phenomena. With i'emi-cauftic potafhit yields an opake coagulum, and being thenmoderately heated the oil melts into one mafs,which on cooling concretes into a brown waxymatter, entirely feparate from the aqueousfluid, from which cryftals of fulphated potafhare depofited by evaporation. Cauftic ammo-nia produces no vifible change at firft:, but ina fhort time caufes the reparation of a coagulumthat is refoluble iti an excefs of alkali, but ifwalhed and melted, exa&ly refembles the pre-cipitate by potafh. Both magnefia and chalkproduce a fimilar coagulation of the oily partof the folution. A like decompofition takesplace by digeftion with cerufle, with filings ofiron or of zinc, with the acetites of lead andcopper, with nitric, muriatic, and ftrong acetousacids, with nitrat of potafh and muriat of am-monia, but not with nitrat of foda, or muriat offoda. The coagulum in all thefe cafes aflumesthe appearance of yellow wax. When the acidfoap is fubjetled to gradual diftillation there firftcomes over a nearly infipid phlegm, and thenan oil more or lefs coloured and rancid, in pro-portion to the deepnefs of its colour, whichcongeals on cooling; there remains in the retorta little carbonaceous matter.
Nitric acid when cold and colourlefs a£ts but{lowly on fixed oils, and the chief vifible efFedfproduced is that of rendering them thicker thanbefore. But if ruddy nitrous acid is made ufeof, a much greater and more rapid alterationtakes place, a violent effervefcence comes on,attended by a copious difcharge of nitrous gas.If a mixture of concentrated fulphuric and veryhigh coloured nitrous acid be fuddenly added,immediate combuftion is for the molt part theconfequence, particularly if the oil is eithernaturally drying or made fo by either of themethods already defcribed. Nitric acid ab-ftrafted upon oil is decompofed, and oxalicacid is the refult. If nitrous vapour or nitrousgas are thrown up into an inverted jar contain-ing, oil, they are rapidly abforbed, and thecolour of the oil is changed to blue or green;after being put for a few hours in a cold place,the oil folidifies, and its colour becomes yellowor orange, a confiderable difengagement of azottakes place, and in the courfe of a few weeksit becomes nearly white and very ftiff. e
Muriatic acid produces little - change inany of the fixed oils, but oxymuriatic acidthickens and bleaches them, and caufes themto pafs nearly into the ftate of wax.
• Prieftley on Air, M
None of the neutral falts are capable of com-bining with oil, nor of decompofing it at thecommon temperature, except the oxymuriatof potafli : this mixed up in a metal mortarwith a few drops of oil, and then ftruck finartlywith the peftle, immediately detonates andtakes fire.
Oil unites pretty eafily with fugar or fimplemucilage, and in this ftate is mifcible withwater into a white emulfive liquor.
The drying oils when mixed with lamp-black,or with almoft any very dry vegetable fibre, andput into a box or clofe room, are very fubjedtto undergo a rapid decompofition attended bygreat heat, which on the admillion of frefh air,burfts into actual Inflammation.
We {hall terminate this article by fome fhortnotices concerning the qualities and method ofpreparation of the principal fixed oils.
The fruit of the olive tree (Olea Europea )when ripe, is of a dark purple colour, and bothin fize and fhape refembles a long plum : itconfifts of a nut or ftone covered by a flefhypulp, in the latter of which are the cells thatcontain the oil: the interior nut alfo containsan oil, but of a bitter difagreeable tafte. Thefruit as foon as gathered is broken in a mill,care being taken to fet the mill-ltones at fuch adiftance as to avoid crufliing the nut of theolive. The pulp thus prepared is put into bagsmade of ru flies, and fubjefted to a moderatepreflure, by which a confiderable quantity of agreenifh femi-tranfparent oil is obtained, whichfrom its fuperior excellence is called virgin oil.The marc remaining after this firft operation isbroken to pieces, moiftened with a little warmwater, and again returned to the prefs ; a mix-ture of oil and water flows out, which foonfeparates fpontaneoufly by reft. This oil thoughinferior to the former, is ftill of a very goodquality and fit for the table. The marc beingagain broken to pieces, drenched with water, andfermented in large cifterns, is for the third andlaft time fubmitted to the full force of the prefs,by which aconfiderablequantity of oil is obtained,very valuable to the fonp-boiler and other manu-facturers. In fome countries, particularly inSpain , the olives inftead of being gathered by-hand, are beaten down, by which the ripe andunripe are mixed together, to thefe alfo are addedfuch as have fallen of themfelves, and are there-fore more or lefs decayed. Of this indifcriminatecollection a large heap is made, which foonbegins to ferment; in this ftate the olives areithodiii. p. Ill, 136.