There is nothing, indeed, said of vinegar in the description of the Egyptian mines before mentioned but Pliny expressly affirms, that it was the quality of vinegar, when poured upon rocks, to split such as an antecedent fire had not split; and that it was the custom of miners to burst the rocks they met with, by fire and vinegar*. This account of Hannibal's using vinegar in splitting the rocks, is generally looked upon as fabulous: for my part, I can easily con. ceive, that a few barrels of vinegar might have been of great use, if the rocks were of the limestone kind; and, whether they were so or not, I leave to be settled by those, who have visited the place where this famous attempt was made. Vinegar corrodes all sorts of limestone and marble rocks; and hence, being introduced into the crack made by the fire, it might be very efficacious in widening them, and rendering the separation of large lumps by iron crows and wedges more easy. It is erroneously supposed, that a large quantity of vinegar was requisite, for the vinegar did not reduce the whole mass of rocks into a pulp; since Livy clearly informs us, that after the action of both the fire and vinegar, they were obliged to open their passage by iron instruments, which would have been wholly unnecessary, had the main body of the rocks been dissolved by the vinegar t. SECTION Composition and Analysis of Gunpowder. GUNPOWDER is an artificial composition, consisting of saltpetre, sulphur, and charcoal. The principal things to be respected in the making of gunpowder are, the goodness of the ingredients; the manner of mixing them; the proportion in which they are to be combined; and the drying of the powder after it is made. Saltpetre, in its crude state, whether it be brought from the East Indies, or made in Europe, is generally, if not universally, mixed with a greater or less portion of common salt: now a small por. tion of common salt injures the goodness of a large quantity of gunpowder; hence it becomes necessary, in making gunpowder, to use the very finest saltpetre. The purest sulphur is that which * Saxa rumpit infusum (acetum) quæ non ruperit ignis antecedens. Plin. Nat. Hist. L. 23. s. 27. & L. 33. s. 21. where by Silices cannot be understood what we call flints, since vinegar has no action on flints. + - ardentiaque saxa infuso aceto putrefaciunt. rupem ferro pandunt. Liv. Hist. I. xxi. c. xxxvii. Ita torridam incendie is sold in shops under the name of flowers of sulphur; but the roll sulphur being much cheaper than the flowers of sulphur, and being also of a great degree of purity, it is the only sort which is used in the manufacturing of gunpowder. With relation to the charcoal, it has been generally believed that the coal from soft and light woods was better adapted to the making of gunpowder, than that from the hard and heavy ones; thus Evelyn says of the hazel, that "it makes one of the best coals used for gunpowder, being very fine and light, till they found alder to be more fit*." And in another place he thinks that lime-tree coal is still better than that from aldert. An eminent French chemist has shewn, from actual experiment, that this opinion in favour of coal from light woods is ill founded; he affirms, that powder made from lime-tree coal, or even from the coal of the pith of alder.tree, is in no respect preferable to that made from the coal of the hardest woods, such as guaiacum and oak . This remark, if it be confirmed by future experience, may be of no small use to the makers of gunpowder; as it is not always an easy matter for them to procure a sufficient quantity of the coal of soft wood. The mixture of the materials of which gunpowder is made, should be as intimate and as uniform as possible; for, in whatever manner the explosion may be accounted for, it is certain that the three ingredients are necessary to produce it. Saltpetre and sulphur mixed together give no explosion; sulphur and charcoal give no explosion; and though saltpetre and charcoal, when intimately mixed, do give an explosion, yet it is, probably, of far less force than what is produced from a mixture of the three ingredients. I have said probably, because this point does not seem to be quite settled at present, as may appear from the following opinions, of two eminent chemists, each of whom ap. peals to experience.-" Un mêlange de six onces de nitre et d'une once charbon produit une poudre qui a moitiê moins de force que toutes celles dans lesquelles on fait entrer du soufre: cette substance est donc absolument essentielle à la composition de la poudre. Dans le temps que je travaillois sur cette matiere, quelques particuliers proposerent de faire de la poudre sans soufre: ils promettoient qu'elle seroit plus forte. La poudre dans laquelle on fait entrer une petite quantité de soufre, augmente de force Evelyn's Silva, by Dr. Hunter, p. 223. + Id. p. 916. du doubl §."-"The principal ingredients of gunpowder, and those to which it owes its force, are nitre and charcoal; for these two ingredients well mixed together, constitute gunpow. der at least equal, if not superior in strength to common gunpowder, (as I found by experience,) and may be seen in the Memoire of Count Saluce, inserted in the Melanges de Philosophie et de Mathematiques, de l'Academic Royale de Turin. The sulphur seems to serve only for the purpose of setting fire to the mass with a less degree of heat *." If I may trust some crude experi. ments which I have made with a common powder trier, I must accede to the opinion of M. Beaumé, as I repeatedly found that equal bulks of common powder, and of the same sort of powder, freed from its sulphur by a gentle evaporation, differed very much both in the loudness and force of the explosion; the powder which had lost its sulphur being inferior to the other in both particulars. It is not without reason, that equal bulks are here specified, for any definitive measure of common powder weighs more than the same measure of powder which has lost its sulphur; hence the re. sult of experiments made with equal weights of these powders, will be different from that which is derived from the explosion of equal bulks may not this observation tend to reconcile the opinions before mentioned? But whether sulphur be an absolutely necessary ingredient in the composition of gunpowder or not, it is certain that an accurate mixture of the ingredients is essentially requisite. In order to accomplish this accurate mixture, the ingredients are previously reduced into coarse powders, and afterwards ground and pounded together, till the powder becomes exceeding fine; and when that is done the gunpowder is made. But as gunpowder, in the state of an impalpable dust, would be inconvenient in its use, it has been customary to reduce it into grains, by forcing it, when moistened with water, through sieves of various sizes. The necessity of a complete mixture of the materials, in order to have good gunpowder, is sensibly felt, in the use of such as has been dried after having been accidentally wetted. There may be the same weight of the powder after it has been dried, that there was before it was wetted; but its strength is greatly diminished on account of the mixture of the ingredients being less perfect. This diminution of strength proceeds from the water having dissolved a * Chym. par M. Beaumé, vol. 1. p. 461. + Philos. Trans. 1779, p. 397, where the reader will find several ingenious xperiments relative to the nature of gunpowder, by Dr. Ingenhousz. portion of the saltpetre (the other two ingredients not being soluble in water ;) for upon drying the powder, the dissolved saltpetre will be crystallized in particles much larger than those were, which entered into the composition of the gunpowder, and thus the mixture will be less intimate and uniform, than it was before the wetting. This wetting of gunpowder is often occasioned by the mere moisture of the atmosphere. Great complaints were made concerning the badness of the gunpowder used by the English in their engage. ment with the French fleet off Grenada, in July 1779; the French having done much damage to the masts and rigging of the English, when the English shot would not reach them. When this matter was inquired into by the House of Commons, it appeared that the powder had been injured by the moisture of the atmosphere; it had concreted into large lumps, in the middle of which the saltpetre was visible to the naked eye. If the wetting has been considerable, the powder is rendered wholly unfit for use; but if no foreign substance has been mixed with it except fresh water, it may be made into good gunpowder again, by being properly pounded and granulated. If the wetting has been occasioned by salt water, and that to any considerable degree, the sea salt, upon drying the pow der, will remain mixed with it, and may so far vitiate its quality, that it can never be used again in the form of gunpowder. However, as by solution in water and subsequent crystallization, the most valuable part of the gunpowder, namely, the saltpetre, may be extracted, and in its original purity, even from powder that has been wetted by sea water, or otherwise spoiled, the saving a damaged powder is a matter of national economy, and deservedly at tended to in the elaboratory at Woolwich. same use. The proportions in which the ingredients of gunpowder are combined together, are not the same in different nations, nor in different works of the same nation, even for powder destined to the It is difficult to obtain from the makers of gunpowder, any information upon this subject; their backwardness in this particular arises, not so much from any of them fancying themselves possessed of the best possible proportion, as from an affectation of mystery common to most manufacturers, and an apprehension of discovering to the world that they do not use so much saltpetre as they ought to do, or as their competitors in trade really do use. Saltpetre is not only a much dearer commodity than either sulphur or charcoal, but it enters also in a much greater proportion into the composition of gunpowder, than both these materials taken together; hence, there is a great temptation to lessen the quantity of the saltpetre, and to augment that of the other ingredients: and the fraud is not easily detected, since gunpowder, which will explode readily and loudly, may be made with very different quantities of saltpetre. Baptista Porta died in the year 1515; he gives three different portions for making of gunpowder, according as it was required to be of different strength*. I have reduced his proportions, so that the reader may see the quantities of the several ingredients, contained in 100 pounds weight of each sort of powder. It is somewhat remarkable, that in all these proportions, the sulphur and charcoal are used in equal quantities. Cardan died about sixty years after Baptista Porta, and in that interval, the proportions of the ingredients of gunpowder seem to have under. gone a great change. Cardan's proportions for great, middle. sized, and small guns, are expressed in the following table*. For great and middle-sized guns, we see, a much greater pro. portion of charcoal than of sulphur was used in Cardan's time; at present, I believe, it is in most places the reverse, or at least the charcoal no where exceeds the sulphur. I have put down the proportions used at present in England, France, Sweden, Poland, and Italy, for the best kind of gunpowder. Mag. Nat, L. XII. c. 3. + Card. Oper. Vol. III. p. 379. |