There are what we term fixed oils, and essential or volatile oils. A list is annexed as given by “Hadyn’s Dictionary of Science”:—
Fixed Oils.
- Drying.
- Linseed oil.
- Poppy oil.
- Sunflower oil.
- Walnut oil.
- Tobacco-seed oil.
- Cress-seed oil.
- Non-Drying.
- Almond oil.
- Castor oil.
- Colza oil.
- Oil of mustard.
- Rape-seed oil.
- Olive oil, etc.
Essential Oils.
- Oil of anise.
- Oil of bergamot.
- Oil of carraway.
- Oil of cassia.
- Oil of cedar.
- Oil of cloves.
- Oil of lavender.
- Oil of lemon.
- Oil of mint.
- Oil of myrrh.
- Oil of nutmeg.
- Oil of peppermint.
- Oil of rose.
- Oil of turpentine.
Vegetable oils are obtained by crushing seeds; animal oils come from the whale and seal tribe. Paraffin oil comes from coal. Linseed is a very drying oil, and on it depends the drying power of paint. We know olive oil will not dry on exposure to the air. Oiled silk is made with linseed oil. When oil is drying in the air considerable heat is evolved, and if oiled substances be left near others likely to catch fire, spontaneous combustion may ensue. Oil of turpentine is found in the pine and fir trees, and many of the oils above mentioned are used by perfumers, etc., the rose oil, or attar of roses, being an Eastern compound.
Fig. 433.—Crushing mill.
Allied to the volatile oils are the RESINS, which are non-conductors of electricity. They are vegetable products. They are soluble in alcohol, in the volatile oils, or in ether, and these solutions are called varnishes; the solvent evaporates and leaves the coating. Turpentine, copal, mastic, shellac, caoutchouc, and gutta-percha are all resinous bodies. Amber is a mineral resin, which was by the ancients supposed to be the “tears of birds” dropped upon the seashore. Moore refers to this in his poetic “Farewell to Araby’s Daughter”—