Caustic potassa has been employed for the separation of the sulphur from the charcoal. It unites with the sulphur, forming a sulphuret; and as sulphuretted hydrogen gas is also produced, the sulphuret must likewise contain the hydroguretted sulphuret of potassa. The charcoal is not acted upon.
M. Vito Caravelli, professor of chemistry at Naples, (Elements d'Artillerie, 1773,) has given a more simple process for the separation of these substances, which depends on their specific gravity. When mixed with water, the sulphur will deposite, and the charcoal float on the fluid.
Vauquelin directed his attention to this subject, and has recommended various processes, not only for the separation of the sulphur and charcoal, but also the nitre.
The process of Smithson Tennant is nearly of the same nature.
The separation of sulphur from charcoal may be effected more perfectly, according to Brande, by introducing the mixture into a small retort furnished with a stop cock, exhausted, and filled with chlorine gas; the chlorine will unite with the sulphur, forming a chloride, and leave the charcoal, which may be washed, dried, and weighed.
Baumé found, that when all the sulphur is expelled which will be driven off in the heat, a certain portion will still remain, and not burn away at a lower temperature than will consume the charcoal; so that to the last the burning residue will smell strongly sulphurous. This retained portion of sulphur he finds, by the results of many other experiments, to be very uniformly about one-twenty-fourth part of the whole sulphur employed; whence, for all common purposes, an adequate correction may be made, by estimating that the slow weak combustion of the residue, after the nitre has been extracted, destroys only 23/24ths of the sulphur instead of the whole. On trying to separate them by an alkaline solution, he found some of the sulphur to remain undisturbed, and still adhering to the charcoal. In consequence of this circumstance, it is recommended, to insure a perfect analysis, to separate the nitre in the first place from gunpowder, by hot water, and to treat the residue with nitric acid. After the sulphur is acidified, the addition of nitrate or muriate of barytes will separate, effectually, the sulphuric acid from the fluid, and form a sulphate of barytes; this being collected, washed, dried, and weighed, will give the quantity of sulphuric acid, and of sulphur in the acid, by the well known proportion of acid in the salt, and of sulphur in the acid. One hundred parts of sulphate of barytes, when perfectly dry, indicate fourteen and a half parts of sulphur; or, which is the same, according to Chenevix, one hundred and fifty-five grains denote twenty-two and a half grains of sulphur.
The observations of M. Champy and professor Proust on humid powder, seem to place the quantity of water absorbed, at 8, 10, and 14 per cent. These proportions, it is evident, depend greatly on the quality of the nitre; and if deliquescent salts exist in any quantity, the absorption, and consequently the increase of weight must be greater. Chemical examination will readily determine this fact.
The different sorts of gunpowder are usually distinguished by marks on the heads of the barrels. Gunpowder marks are various. All gunpowder for service is mixed in proportions according to its strength, so as to bring it as much as possible to a mean and uniform force. This sort of powder, says Adye, (Bombardier and Pocket Gunner,) is marked with a blue L. G. and the figure 1/2; or with F. 1/2 G. and the figure 3, whose mean force is from 150 to 160 of the eprouvette. This is the powder used for practice, for experiments, and for service. The white L. G. or F. G. is a second sort of powder of this quality. It is sometimes stronger but not so uniform as the L. G. It is, therefore, generally used in filling shells, or such other things as do not require accuracy. The red L. G. F. G. denotes powder in the British service, made at the King's mills, with the coal made in cylinders, and is used at present only in particular cases, and in comparisons, and to mix with other sorts to bring them to a mean force. The figures 1, 2 or 3 denote that the powder is made from saltpetre, obtained from the rough. Other marks are also in use to designate the rifle, musket, cannon powder, and the like.
Powder merchants recover damaged gunpowder, by putting a part of the powder on a sail cloth, and adding an equal quantity of good powder, which is well mixed with it, and the mixture is then dried.
Sec. VIII. Of Lampblack.