It may be purified by agitating 100 parts oil with 1 parts chloride of lime and 12 water; a small quantity of decoction of oak hark is afterward added to remove; all traces of gelatinous matter which it retains, and the mixture is left to settle. The clear oil is afterward agitated with a small portion of sulphuric acid, again clarified by subsidence, and washed to remove adhering Sulphuric acid. The addition of mineral oils, as heavy kerosene, has also the tendency to prevent gumming, or at least greatly to diminish it.

Oils, Volatile, Explosion of. A mixture of 2 parts of perfectly dry permanganate of potassium with 2 or 8 parts of concentrated sulphuric acid is a most powerful oxidizing agent, owing to the separation of permanganic acid and its immediate decomposition with the liberation of oxygen. Volatile oils are violently affect ed by this mixture, if about 10 drops are placed in a little dish and then touched with a stout glass rod previously dipped into the mixture. The following produce explosions, often most violently: oils of thyme, mace, turpentine (rectified), spike, cinnamon, origanum, rue, cubebs, and lemon. The following oils are simply inflamed, particularly if poured upon blotting-paper and touched with the mixture, though under certain still unknown circumstances explosion may occur: oils of rosemary, lavender, cloves, rose, geranium, gaultheria, caraway, cajeput, bitter-almond, and rectified petroleum. The following substances are ignited without explosion: alcohol, ether, wood-spirit, benzole, chlorelayl, sulphide of carbon, and cotton. Gun-cotton and gunpowder are not ignited.