By referring to the article on Greek fire, and some incendiary preparations used in war, it will be seen, that camphor is an important constituent. As camphor is very combustible, and will even burn on the surface of water, it is well adapted for all those purposes. We have already spoken of the Greek fire; and it seems, that the peculiar character of that fire, of burning in water, was owing to the presence of camphor. This opinion appears plausible, when we consider, that some preparations have been made with camphor, which had the property of burning on water.
Camphor may be pulverized by the assistance of, and brought into intimate mixture with, nitre and sulphur; because the former, in particular, tends to divide it. But it may be pulverized separately, and afterwards added to the composition, by rubbing it in a mortar with a small quantity of alcohol, or spirit of wine; or, if this cannot be had, with fourth proof brandy. As camphor is very inflammable, its effects, when mixed with saltpetre and fired, are much the same as those produced by other resins, or concrete oils. A combustion, more or less rapid, ensues, and, while the nitre itself is decomposed, the camphor also undergoes the same change, producing both water and carbonic acid, from the union of two of its elements, the hydrogen and carbon, with the oxygen of the nitric acid. In all cases, in which camphor is employed in artificial fire-works, although its own flame is white, it may assist in increasing the flame, which, however, is modified, according to the substances, which enter into the composition. These may not retard its combustion, but, nevertheless, may change the appearance of the flame; as is the case, when we employ the filings of iron, steel, brass, or zinc, sal ammoniac, rosin, saw-dust, and other substances, which usually form a part of such mixtures. Upon the whole, then, we may consider, that camphor acts in fire-works; 1st, as an inflammable body; 2ndly, that, besides being in a great measure decomposed, a portion of it is evaporated, and communicates, to the surrounding atmosphere, a peculiar smell, which is recognised in the odoriferous fire-works; 3rdly, that, while it acts in taking a part of the oxygen from the nitric acid of the nitre, it assists in the decomposition of this salt, more especially if it be mixed separately with the nitre; 4thly, that, in all instances of its combustion, while it acts primarily on the nitre, with the oxygen of which it forms both water and carbonic acid, it, at the same time, increases the flame, which may be either white, red, or yellow, according to the other substances employed; and, finally, it may be thrown out in the state of combustion, and receive, for the further support of its combustion, the oxygen of the air, and hence produce a white exterior flame, while that in the immediate vicinity of the composition may be more or less coloured. But its application, the proportions in which it is used, as well as the kind of fire-works to which it is applicable, will be considered at large in other parts of the work.
The great inflammability of camphor is to be ascribed to its containing a large quantity of carbon and hydrogen, and a small quantity of oxygen.
There is a preparation, called artificial camphor, that is formed by passing muriatic acid gas through spirit of turpentine. It inflames with facility, and burns, without leaving any residue. Might not this preparation be economically employed, in lieu of camphor, for incendiary fire-works?
Sect. XVI. Of Gum Benzoin, and Benzoic acid.
Gum Benzoin, or Benjamin, is considered a solid balsam, and is the production of a tree, which grows in Sumatra, &c. called the styrax benzoe. It is obtained from this tree by incision, a tree yielding three or four pounds. It is a brittle substance, sometimes in the form of yellowish-white tears and called, from that circumstance, almond benzoin. Besides a resinous substance, it contains an acid, called the benzoic or flowers of benzoin, a substance similar to balsam of Peru, being a peculiar aromatic principle, soluble in alcohol and water. By heating it, or by combustion, it evolves a very agreeable smell, and is, therefore, used in those fire-works which are exhibited in rooms, theatres, &c. and also in the composition of odoriferous fire-works. Besides being in itself inflammable, it produces a peculiar smell, arising, in all probability, from an essential oil, aided, in some degree, by the separation of benzoic acid.
It has been examined by Bucholz and Brande. Its general properties are: that it is insoluble in water, although hot water takes up a part of it, said to be the benzoic acid. It is soluble in alcohol, from which it is separated by muriatic and acetic acids, but not by the alkalies. It is also soluble in ether.
The benzoic acid, or flowers of benzoin, are obtained from it by sublimation. A quantity of the powdered gum, put into an earthen basin, a thick paper cone being tied round the rim, and heat applied, the acid will leave the resin, and be condensed on the inner side of the cone. Bucholz (Bulletin de Pharmacie, v. p. 177) has given a process for obtaining it by means of alcohol, and some others have been adopted. By boiling four ounces of the gum in powder in a sufficient quantity of water, with three drachms of carbonate of soda, the acid will unite with the alkali, and form a benzoate of soda, which, when filtered and decomposed by sulphuric acid, will yield the benzoic acid. Five drachms of acid will be thus obtained. Lime has been used in the same manner as soda, and the acid separated by the addition of muriatic acid.
Flowers of benzoin may be used in the place of the gum; using, however, but a small quantity. They will communicate the same odour to fire as the benzoin. The flowers, or acid of benzoin, are so inflammable, as to burn, with a clear yellow flame, without the assistance of a wick. It is soluble in ardent spirits, in oils, and in melted tallow. The compounds, which it forms with them, are also inflammable. Benzoic acid is considered to be an oily acid, and contains, no doubt, a very large proportion of hydrogen.
Sect. XVII. Of Storax Calamite.