In the practical part of Pyrotechny, the constructing and due proportioning of the moulds is a very material consideration, for on these the goodness of the article depends nearly as much as on the purity of the ingredients. They consist chiefly of solid and hollow cylinders made either of wood or metal; those that are hollow are calledmoulds, and those that are solidformers; both are used in the construction of rockets; similar cylinders either of wood or metal are used for ramming down the composition; a machine for contracting the aperture of the cases, the operation of which is calledchoaking; another for boring them after they are filled; and a simple apparatus for grinding the materials previous to the cases being filled, as well as others of less importance, which we shall choose rather to describe as their assistance is required.
We shall begin the important Apparatus with describing those which come most immediately into use.
1.Grinding Machines.—For the purpose of triturating or properly mixing the several ingredients together, various contrivances have been resorted to. A common iron mortar, such as is used by druggists and apothecaries, is found to answer very well for grinding or pounding the brimstone, charcoal, salt-petre, &c.separately; and apothecary’s close sieves, fitted with wire-cloth, are the best possible implements for obtaining the fire powder; but when corn gunpowder is to bemealed, or the various ingredients are to be mixed together, such mortars cannot be used, as the heat generated by the continued action of the pestle might inflame the mixture, and thereby place the life of the operator in imminent danger. To obviate these dangerous probabilities a very simple contrivance has been effected; this is called the mealing table, and for that purpose has proved very speedy and effectual. It consists of a rectangular elm board, with a rim round its edge, four or five inches high, at one end of which a part of the rim is made toslide in a groove, so that after mealing the powder it may be swept clean out from the table. A representation of it may be seen at plate 1,fig. 3. Fig. 4is a small copper shovel, generally made use offor filling and emptying the table. When about to meal a quantity of powder, observe not to put too much on the table at once; but when you have put on a moderate portion, take the muller (fig. 5,) and rub it till all the grains are well broken; then sift it in a lawn sieve, that has a receiver and top to it, such as is generally used by the apothecaries, and that which does not pass through the sieve must be returned to the table, and with an additional quantity ground over again. Sulphur and charcoal may be ground in the same manner, only these being much harder than powder the muller must be of ebony, or any other hard wood, else the ingredients would stick in the grain of the elm, and be very difficult to grind. As sulphur is apt to stick and clod to the table, it will be found best to have one for that purpose, as they are easily procured; this will be but little trouble, and more than compensated by your sulphur being always kept clean and well ground.
The following is another method for the above purpose, which some consider equally effective. This is a mortar made of hard wood, shaped like that of the druggists, with the bottom rounded within, and having a wooden lid fitting close on the top, and in the centre a hole just large enough to admit easily the stalk of the pestle, to the lower endof which is connected a piece of marble terminating in a spherical surface. With this apparatus gunpowder may be safely ground to meal, or its ingredients mixed by the continued motion of the pestle in the hole of the lid.
2.Method of mixing the Ingredients.—Connected with that of grinding is the operation of mixing the ingredients, and which is considered a principal part of the business of Pyrotechny; and indeed many articles depend as much on the well mixing as on the proportion of their composition; therefore great care should be taken in this part of the work, and particularly so in the composition of sky-rockets. When you have about four or five pounds of ingredients duly prepared for mixing, (which is a sufficient quantity to mix at one time,) first put them together in some vessel convenient for the purpose, then work them about with your hands, till their various natures are pretty well incorporated; after which put them into your lawn sieve with the receiver and top to it, and sift it into some other clean vessel, and if any remains that will not pass through the sieve, grind it again till fine enough; and if it be suffered to pass twice through the sieve it will be more than the trouble the better. For rockets and all fixed works, from which the fire is to play regular, the ingredients must be prepared asabove; and we may observe here, that all compositions which contain steel or iron filings must be mixed or shifted with the copper shovel, for the hands are apt to impart a moisture, which is injurious to their nature. Nor will any works which have iron or steel in their charge keep long in damp weather without being properly prepared, as was directed in the preceding Section.
There are several other moulds and apparatus made use of, but as most of them are used in the making of rockets, and some few other articles, and are so immediately connected with the practice thereof, we think their use and application will be better understood when we come to treat of that article in the next Section, rather than by entering their descriptions in this place.