Essential oils

Oil \Oil\ (oil), n. [OE. oile, OF. oile, F. huile, fr. L. oleum;
   akin to Gr. ?. Cf. {Olive}.]
   Any one of a great variety of unctuous combustible
   substances, more viscous than and not miscible with water;
   as, olive oil, whale oil, rock oil, etc. They are of animal,
   vegetable, or mineral origin and of varied composition, and
   they are variously used for food, for solvents, for
   anointing, lubrication, illumination, etc. By extension, any
   substance of an oily consistency; as, oil of vitriol.
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   Note: The mineral oils are varieties of petroleum. See
         {Petroleum}. The vegetable oils are of two classes,
         {essential oils} (see under {Essential}), and {natural
         oils} which in general resemble the animal oils and
         fats. Most of the natural oils and the animal oils and
         fats consist of ethereal salts of glycerin, with a
         large number of organic acids, principally stearic,
         oleic, and palmitic, forming respectively stearin,
         olein, and palmitin. Stearin and palmitin prevail in
         the solid oils and fats, and olein in the liquid oils.
         Mutton tallow, beef tallow, and lard are rich in
         stearin, human fat and palm oil in palmitin, and sperm
         and cod-liver oils in olein. In making soaps, the acids
         leave the glycerin and unite with the soda or potash.
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   {Animal oil}, {Bone oil}, {Dipple's oil}, etc. (Old Chem.), a
      complex oil obtained by the distillation of animal
      substances, as bones. See {Bone oil}, under {Bone}.

   {Drying oils}, {Essential oils}. (Chem.) See under {Drying},
      and {Essential}.

   {Ethereal oil of wine}, {Heavy oil of wine}. (Chem.) See
      under {Ethereal}.

   {Fixed oil}. (Chem.) See under {Fixed}.

   {Oil bag} (Zool.), a bag, cyst, or gland in animals,
      containing oil.

   {Oil beetle} (Zool.), any beetle of the genus {Meloe} and
      allied genera. When disturbed they emit from the joints of
      the legs a yellowish oily liquor. Some species possess
      vesicating properties, and are used instead of
      cantharides.

   {Oil box}, or {Oil cellar} (Mach.), a fixed box or reservoir,
      for lubricating a bearing; esp., the box for oil beneath
      the journal of a railway-car axle.

   {Oil cake}. See under {Cake}.

   {Oil cock}, a stopcock connected with an oil cup. See {Oil
      cup}.

   {Oil color}.
   (a) A paint made by grinding a coloring substance in oil.
   (b) Such paints, taken in a general sense.
   (b) a painting made from such a paint.

   {Oil cup}, a cup, or small receptacle, connected with a
      bearing as a lubricator, and usually provided with a wick,
      wire, or adjustable valve for regulating the delivery of
      oil.

   {Oil engine}, a gas engine worked with the explosive vapor of
      petroleum.

   {Oil gas}, inflammable gas procured from oil, and used for
      lighting streets, houses, etc.

   {Oil gland}.
   (a) (Zool.) A gland which secretes oil; especially in birds,
       the large gland at the base of the tail.
   (b) (Bot.) A gland, in some plants, producing oil.

   {Oil green}, a pale yellowish green, like oil.

   {Oil of brick}, empyreumatic oil obtained by subjecting a
      brick soaked in oil to distillation at a high temperature,
      -- used by lapidaries as a vehicle for the emery by which
      stones and gems are sawn or cut. --Brande & C.

   {Oil of talc}, a nostrum made of calcined talc, and famous in
      the 17th century as a cosmetic. [Obs.] --B. Jonson.

   {Oil of vitriol} (Chem.), strong sulphuric acid; -- so called
      from its oily consistency and from its forming the
      vitriols or sulphates.

   {Oil of wine}, [OE]nanthic ether. See under {[OE]nanthic}.

   {Oil painting}.
   (a) The art of painting in oil colors.
   (b) Any kind of painting of which the pigments are originally
       ground in oil.

   {Oil palm} (Bot.), a palm tree whose fruit furnishes oil,
      esp. {Elaeis Guineensis}. See {Elaeis}.

   {Oil sardine} (Zool.), an East Indian herring ({Clupea
      scombrina}), valued for its oil.

   {Oil shark} (Zool.)
   (a) The liver shark.
   (b) The tope.

   {Oil still}, a still for hydrocarbons, esp. for petroleum.

   {Oil test}, a test for determining the temperature at which
      petroleum oils give off vapor which is liable to explode.
      

   {Oil tree}. (Bot.)
   (a) A plant of the genus {Ricinus} ({Ricinus communis}), from
       the seeds of which castor oil is obtained.
   (b) An Indian tree, the mahwa. See {Mahwa}.
   (c) The oil palm.

   {To burn the midnight oil}, to study or work late at night.
      

   {Volatle oils}. See {Essential oils}, under {Essential}.
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Essential \Es*sen"tial\ ([e^]s*s[e^]n"sjal), a. [Cf. F.
   essentiel. See {Essence}.]
   1. Belonging to the essence, or that which makes an object,
      or class of objects, what it is.
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            Majestic as the voice sometimes became, there was
            forever in it an essential character of
            plaintiveness.                        --Hawthorne.
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   2. Hence, really existing; existent.
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            Is it true, that thou art but a name,
            And no essential thing?               --Webster
                                                  (1623).
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   3. Important in the highest degree; indispensable to the
      attainment of an object; indispensably necessary.
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            Judgment's more essential to a general
            Than courage.                         --Denham.
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            How to live? -- that is the essential question for
            us.                                   --H. Spencer.
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   4. Containing the essence or characteristic portion of a
      substance, as of a plant; highly rectified; pure; hence,
      unmixed; as, an essential oil. "Mine own essential
      horror." --Ford.
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   5. (Mus.) Necessary; indispensable; -- said of those tones
      which constitute a chord, in distinction from ornamental
      or passing tones.
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   6. (Med.) Idiopathic; independent of other diseases.
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   {Essential character} (Biol.), the prominent characteristics
      which serve to distinguish one genus, species, etc., from
      another.

   {Essential disease}, {Essential fever} (Med.), one that is
      not dependent on another.

   {Essential oils} (Chem.), a class of volatile oils, extracted
      from plants, fruits, or flowers, having each its
      characteristic odor, and hot burning taste. They are used
      in essences, perfumery, etc., and include many varieties
      of compounds; as {lemon oil} is a terpene, {oil of bitter
      almonds} an aldehyde, {oil of wintergreen} an ethereal
      salt, etc.; -- called also {volatile oils} in distinction
      from the fixed or nonvolatile.
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