The traditional account of so recent a discovery as that of Galvani, is the preparation of frog soup for his wife, and the accidental touching one of them with the knife; while, in fact, he had been for years employed in examining the convulsive action of frogs, and had presented several memoirs to the Institute of Bologna on the subject, before its general publicity; indeed, in the main fact he had been anticipated by Swammerdam, and he possibly by others.
Schwartz, the monk of Cologne, probably had a real existence, probably had something to do with the progress of pyrotechnic art; it is even more probable that he invented gunpowder than that the public invented him. The very accident which is reported to have happened, it is not altogether improbable did happen; but if a mixture of saltpetre, sulphur, and charcoal accidentally exploded, it was not accident which brought together those particular three ingredients out of the whole laboratory of nature and art.
It is indeed possible that the frequency of accidental explosions when gunpowder was known, were reflected back as a plausible hypothesis to account for its invention; but as the explosive power and utility of gunpowder were not facts which could have been arrived at by a priori reasoning, there is every likelihood of such an accident having originally suggested the application of an explosive mixture as a means of propulsion. The history of the invention then resolves itself into the question, Were any admixtures of these three ingredients previously known, what led to them, and what were the objects proposed by them? This question is attempted to be answered by the book before us, containing a very erudite inquiry into the progress of the invention of Greek fire and gunpowder, which are, according to the author's view, modifications of the same thing, i.e. pyrotechnic compositions, differing only or mainly in the proportions or purity of their ingredients. A mass of very curious information is given to the reader, which, in addition to the general stock of knowledge or obscure tradition on this subject, shows a gradual and generally diffused use of sulphur, saltpetre, and charcoal in different proportions, and occasionally mixed with other combustible substances. Among the Arabs of the thirteenth century a vast number of receipts for such mixtures existed; this is proved by some ancient Arabic MSS. preserved in the Bibliothèque Royale. How the Arabs got possession of these arts is left somewhat in obscurity, though our authors consider there are strong grounds for conjecturing that they obtained then originally from the Chinese about the ninth century; that they then proceeded slowly in improving this knowledge for the three centuries during which they had no intercourse with the Chinese; and that they again acquired further information on these points after the Mongul irruption in the thirteenth century.
The defect of the book before us is its inconclusiveness: from the preface we are led to expect the solution of a theorem; after reading the book through, we find ourselves not indeed as far at sea as ever, but aided mainly by negations. The actual origin of gunpowder or Greek fire is not traced; many of the connecting links in the chain of pyrotechnic discovery are still deficient; and the conjectures, which stand in the place of conclusions, are frequently founded upon what appear to us insufficient data. On the other hand it must be admitted, that on a subject so involved in obscurity, inasmuch as proof is impossible, speculation is to a certain extent admissible as a link to render isolated facts intelligible.
It may be well here if, before passing to the more immediate object of this paper—viz. a sketch of the probable progress of pyrotechny—we explain to those of our readers who are unacquainted with chemistry, the philosophy of explosive combustibles.
Combustion is nothing else than rapid chemical union, taking place between two dissimilar substances, which have what is called an affinity for each other, i.e. a tendency to unite and form a new compound. When a candle or lamp is burned, it is carbon and hydrogen, the principal constituents of oil or fat, which combine with oxygen, one main ingredient of the atmosphere. As it requires a certain temperature for this union to take place, to prevent the cooling effect of mass, a wick is used which can be readily heated, and where, as soon as chemical action has once taken place, other portions of the oil or melted tallow are absorbed, which ascend just as water through the pores of a sponge, and supply the place of those burned. In this example, only a small ignited surface is exposed to the influence of the oxygen: if, however, this latter element could be obtained in a solid state, and mixed up with the combustible, each particle throughout the whole mass would have in contact with it a particle of oxygen; so that, if the whole were raised to the necessary temperature for combustion, combustion would be instantaneous—or if the temperature of a part were sufficiently elevated, the combustion of this portion would communicate an intense heat to the contiguous portions, and the whole would rapidly kindle as a fuse does. In this case also, the access of the air being immaterial, combustion might take place in a closed vessel, or even under water.
Nitre, or saltpetre, is one of a class of substances which contains a large portion of oxygen in a combined and solid state; and, being mixed with combustible matter such as charcoal, it causes rapid deflagration when the temperature is raised. The whole class of pyrotechnic compositions are reducible to this simple principle—they all consist of combustible substances intimately mixed with substances containing oxygen; or, to reduce the proposition to more general and simple terms, they consist of two or more substances, having for each other a powerful chemical affinity, and capable of rapidly uniting when the temperature is elevated. When a projectile force is necessary, a further condition is essential, viz., that they liberate by their chemical action gaseous matter, whereby a sudden increase in volume is produced, the expansion of which, augmented by the high temperature, produces the required effect of propulsion.
This slight sketch will show that the purity and proportions of the saltpetre, and the inflammable substances mixed with it, are the main elements to be attended to in the improvement of self-burning compositions: it is indeed far from improbable, that the substances used in purifying saltpetre have first suggested such compounds. Wood ashes were used at a very early period for purifying nitre; and at the end of an Arabic receipt of the thirteenth century, for the preparation of saltpetre, in which charcoal is used, is the expression, "guard against sparks of fire."
The probabilities strongly favour the view, that incendiary compositions of the nature we have been describing originated with the Chinese. China snow, and China salt, are the names given by writers of the greatest antiquity to saltpetre. In the Arabic MSS. to which we shall presently allude, the words Chinese wheel, Chinese flower, Chinese dart, occur as appellatives of different fireworks. It is very possible that the influx of Chinese literature, which the result of the recent war with that people promises us, will lead to the discovery of Chinese treatises upon pyrotechny.
Other authors speak of fire-arms among the Chinese at a very early period of our era, and even before Christ; but the interpretation which they have put upon obscure passages—interpretations evidently derived from their existing knowledge—makes these expressions and translations of extremely doubtful import.