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_. Morey (_Silliman's Journal_, vol. ii, p. 121) observes, that a small quantity of spirit of turpentine being added to a mixture of iron-filings, sulphuric acid, and water, the hydrogen gas produced, will burn with a very pleasant white flame, and without smoke. He also observes, that, if the vapour of spirit of turpentine be made to pass through a tube, covered at the upper end with a fine wire gauze, it burns with much smoke; but, if a quantity of atmospheric air be allowed to mix with it, the smoke ceases, and the flame continues white. If more still be added, the flame lessens, and becomes partly blue. By adding still more and more, it will burn with a very small flame, entirely blue, and with a singular musical sound. If still more be added, the flame, and every ray of light cease; but that the combustion still continues, is certain, from the explosive detonating noise, continuing to be distinctly heard.