All these substances enter into the composition of fire-works, either to increase the rapidity of combustion, as in incendiary fire-works, or, in some cases, as with rosin, to produce a coloured flame. That they contain carbon and hydrogen, as their principal ingredients, is well known; to which we may attribute their rapid combustion, and the facility with which they decompose nitrous salts. The Greek fire, for example, owed, it is said, its powerful effect to turpentine, which, with other substances employed, made the composition remarkably inflammable, and the decomposition of the nitre, (which some say it contained) so rapid, as even to defy the action of water.
All of the turpentines are obtained from different species of pinus. Common turpentine is the resinous juice, which exudes chiefly from the Pinus Sylvestris, or Scotch fir, and is obtained by boring holes into the trunks of the trees, early in the spring, and placing vessels beneath for its reception. This turpentine, and in fact all others, are composed of rosin and a volatile oil. The latter is obtained by distilling the turpentine with water. It passes over with the water, from which it is afterwards separated, and is then known by the name of the essential oil, or spirit of turpentine. The substance, remaining in the still, is common rosin, or yellow rosin, known likewise by the names of fidlers' rosin and colophony. Tar is also obtained from the roots and refuse parts of the fir tree, by cutting them in billets, piling these in a proper manner, in pits or ovens, formed for the purpose, covering them partly over, and setting them on fire. During the combustion, a black and thick matter, which is tar, falls to the bottom, and is conducted into barrels.
Pitch is nothing more than tar boiled down to a solid consistence; it is usually made, however, by melting together coarse hard rosin, and an equal quantity of tar. The ancient pitch possessed a flavour and fragrance. White pitch is the same as the white turpentine.
Melted pitch, sulphur, and camphor, mixed, when nearly cold, with pulverized saltpetre, and afterwards thinned with spirit of turpentine, will form a composition, that is very inflammable, and will almost resist the action of water. A similar composition must have formed the Greek fire, of which, according to Beckman, there were several kinds.
The turpentine trees furnish various products: Thus, the Pinus Abies, or spruce fir, yields the Burgundy pitch, and its branches produce the Essence of Spruce; but other species of pinus are used for the same purpose, which are nearly allied to it, and which grow abundantly in Canada. From the Pinus laryx, or larch, Venice Turpentine is obtained; but that sold, is usually made by melting rosin, and adding the spirit of turpentine. From the sap of the larch, the Russians prepare a gummy substance, known in Russia by the name of Orenburg gum. Turpentine is extracted in France, in great quantity, from the pinus maratima. Gallipot, colophony, tar, pitch, &c. are likewise obtained from it.
The turpentine of cedar, according to Dr. Pocoke (Travels through Egypt) was employed by the Egyptians for embalming, the operation being performed in several ways. It was injected, and used with salt, nitre, &c.
Pitch, tar, and turpentine all enter into sundry compositions, used in war. The different incendiary preparations, noticed in the last part of the work, are composed, in general, of either one or all of these substances. Their use is obvious. Being very inflammable, and brought in contact with gunpowder, nitrate of potassa, &c. they burn with great rapidity, and consume every thing before them. Hence the tourteaux of the French, tarred links, and fascines, carcasses, &c. owe their effect to the presence of these substances.
Rosins are considered to be volatile oils, saturated with oxygen.
Thus, or frankincense, of which there are several varieties, has been long used in fire-works; it is frequently employed in the composition of odoriferous fire. It is obtained from the pinus abies, and appears in tears. During winter, the wounds made in fir trees become incrusted with a brittle substance, called barras or gallipot, consisting of rosin united with a small portion of oil. All rosins, according to the experiments of Gay-Lussac, and Thenard, (Recherches physico-chimiques) are composed of a great quantity of carbon and hydrogen, united with a small quantity of oxygen. To this, we attribute their great inflammability, and it enables us to account for the rapid decomposition of nitre, in those preparations, in which nitre and resinous substances are employed. See [General Theory of Pyrotechny], sec. ii.
For the accension which takes place by mixing oil of turpentine and nitric acid, see the properties of nitric acid, under the head of [nitre.]