Page:Popular Science Monthly Volume 6.djvu/742

722 from Holland and Germany. The alders and willows in the plantations of the factory furnish but an insignificant supply, probably not enough to make a dozen barrels in the year. They are grown for the most part to form screens around and between the houses, so as to diminish the danger resulting from a possible explosion. The wood employed is of three kinds—alder and willow, which are used for common powder, and black dogwood for fine rifle-powder for the Snider and Martini-Henry. The latter wood is really a kind of buckthorn (Rhamnus frangula), of slow growth, and consequently close grain, which forms dense thickets in the forests of Germany, and is also found in the north of England and elsewhere. It is imported in bundles of slender rods about six feet long, and enormous quantities of these bundles may be seen stacked in the fields of the factory. There it is kept for at least three years, though generally it is allowed to lie in store for a much longer time. Some wood has been kept for twenty years, protected from the weather by a roof of thatch, and is still perfectly sound. Strange to say, comparatively little dogwood is used in the powder-factories of Germany, though it is quite certain that it supplies the best charcoal for the purpose. The old plan for charring wood was to burn it in pits, and this is still the practice abroad, but for many years the charcoal at Waltham has been manufactured by sawing the wood into short lengths, and packing it into iron cylinders called "slips," which are placed on a small carriage, and run into a retort very like those used in gas-works. Here the slip is exposed to the flames for a period varying from two and a half to three and a half hours, the gas issuing from the wood in the process being utilized as fuel; and the superintendent of the work knows when the wood is completely charred, by the peculiar color with which the combustion of the gas tinges the fire. As soon as this appears, the slip is withdrawn and cooled. The charcoal when taken out is ground in a machine like a colossal coffee-mill, and then, like the sulphur, sifted in a slope-reel.

The three ingredients are now ready for the regular process of manufacture to be commenced. Up to a certain, point (the formation of the "press-cake") the process is the same for whatever purpose the gunpowder is intended, but at that point it divides into two branches, according as it is to be used for heavy guns or smaller weapons. We shall, therefore, first trace the various stages of the manufacture up to the press-house, and then explain the method of making the various kinds of gunpowder, and the objects desired to be obtained by these modifications.