Oils, whether essential or fixed, when passed through ignited tubes, are decomposed, and furnish an inflammable gas called olefiant gas. Wax, tallow, &c. produce the same gas, the hydroguret of carbon. Messrs. Taylor and Martineau contrived an ingenious apparatus for generating gas from oil on the great scale, as a substitute for candles, lamps, and coal gas, it being much preferable for burning, as it contains no sulphur, and does not injure furniture, books, plate, paint, &c. Oil gas contains more hydroguret of carbon than coal gas, which is a great advantage, enabling one cubic foot of oil gas to go as far as four of coal gas. An elegant apparatus was erected by Taylor and Martineau at the Apothecaries' Hall, London, a drawing of which may be seen in the 15th number of the "_Journal of Science and the Arts_." It is to be observed, that odoriferous fire-works are intended for exhibition in close apartments; so that the smell of certain gases, produced by the nitre, charcoal, and sulphur, according to the preparation used, will be more or less destroyed. Such preparations are, nevertheless, expensive, and for that reason seldom used. _Sect. XIX. Of Mastich._ This resin, obtained, from the _pistacia lentiscus_, by making transverse incisions in the tree, is first in a fluid state, and gradually concretes into yellowish semi-transparent brittle grains. In Turkey, great quantities of it are used for sweetening the breath, and strengthening the gums. It is from the use of the resin as a _masticatory_, that its name is said to be derived. It is not completely soluble in alcohol, a soft elastic substance separating from the solution. When exposed to heat, it melts, and exhales a fragrant odour: for which reason, principally, it enters into the composition of some fire-works, as the _scented paste_. In ordinary fumigations, mastich is commonly used. _Sect. XX. Of Copal._ Gum copal, by which name it is known, is a resin, obtained from a tree, called _thus copallinum_. It is often in the form of a beautiful white resin; but sometimes it is more or less coloured. It is frequently opaque. It may be dissolved in alcohol, spirit of turpentine, and oils, by a peculiar management, (by using camphor, previously melting it, and the like,) and then it forms the various copal varnishes, which are more or less perfect, as the copal is transparent, and the solution properly formed. When heated, it melts like other resins, and in this, and many other properties, it partakes of the character of resins in general. It is used in some of the formulæ for fire-works. _Sect. XXI. Of Myrrh._