[TOOLS.]
Fig. 132. A port-fire holder. This is made of steel, somewhat after the manner of a pair of pliers. The ends a and b are fluted, or channelled (semi-cylindrical) to receive the port-fire: a spring, riveted at c, holds it tight; by pressing on d, the burnt case drops: the end e is pointed, to enter a long stick, bored to receive it, and strengthened with a brass ferrule.
As an instrument of this kind can be obtained only when made to order, the following contrivance will serve the purpose of most amateurs. First charge some little port-fires, 3 inches long and 1⁄4 inch diameter, till within about 11⁄4 inch full: having filled a couple of dozen, or so, invert them, and knock out the dust, as with squibs; then encircle the whole, as if going to bang them; but pour in dry sand instead; empty a little sand from each, and stop the end with plaster of paris. Scrape out a little composition from the other end, and prime it with damped meal. Take two inches of a roman candle case, or a piece of turned wood, with a hole through it, fig. 133, two inches long. Have a long stick, fig. 134; cut the end, a, so that it will fit the hole in fig. 133, and enter half way up. At the other end fix a wire, z, two and a half inches long. By slipping fig. 133 on fig. 134 it is evident one inch vacancy is left to receive the sand end of the port-fire; when this is burnt out, it can be pushed out with the wire, z.
[TO CONSTRUCT A STEELYARD SCALE.]
The numerous formulæ for coloured fires, renders the use of very small scales excessively troublesome; and there is perpetual danger of losing the little weights for grains and pennyweights. By constructing a steelyard scale, the greatest facility is attained, one weight answering for all.
Take a piece of deal, fig. 135, about as thick as a venetian-blind lath; it may be 20 or 24 inches long; an inch broad, at the left end; and about 1⁄2 an inch broad in the main length. Make a hole at a, twice the diameter of a pin: the same at b. It is necessary to observe that the hole, a, must be on a level with the top of the long arm; if it should be a little higher, it would not be of any consequence; but it must, on no account, be lower. Have a piece of deal, fig. 136, about an inch square, and mortise a hole in it, as drawn. Fix 135 in 136 so as to appear like 137. A bit of a common pin, or needle, is to go through the mortise and through the hole, a, of 135. See that it plays easily. At s, fig. 137, insert a piece of wire, bent like the figure 8; and to it, tie the strings fastened to w, which may be a copper bowl, or a tin patty-pan. The mode of fastening the threads to the figure of 8 wire, is simply to slip them through, bend them down, and tie round with thread, as at z.
Take a piece of brass tube, an inch, or so, long, fig. 138, and with some lead, melted in the bowl of a pipe, fix a bit of wire in it, bent like a staple, or the capital letter U, as drawn. This is for a weight. Slip it on the arm of fig. 137; put a wooden pin in the hole y, to keep the weight from falling off. Slip the weight along, till it balances the patty-pan w: suppose this point is at m. This will be the starting-point. From m to y lay off a number of equal distances, as eighths of an inch. Number them, and the scale is complete. If it be desired that 100 of these divisions should weigh 1 ounce, an ounce weight must be put in the patty-pan w, and the weight shifted along, until it balances; the intervening space must, then, be divided into 100 equal parts. It is desirable to construct two; one with a large weight, that will weigh 8 or 10 ounces; one with a small weight, to weigh the 1⁄100th part of an ounce. This may be of wood, with a wire staple, about the thickness of a patent short-white pin. Nothing can be more convenient than these steelyard scales, as one weight answers for all, and never drops, and gets lost. It is well to have even a third steelyard scale. This may be made very thin, with a piece of wire, bent to the shape of fig. 171, for a weight. It may be made to weigh only the fifth part of an ounce; so that if divided into 100 equal parts, it will weigh the 1⁄500th part of an ounce; so that in trying a new colour, as little can be mixed as will charge only one or two pill-boxes. A little notch should be made, at every division, with a fine, triangular file, to prevent the weight from slipping: every tenth division can be numbered; this is best done with a blacklead pencil, as ink runs; and on the end s, fig. 137, mark how many to the ounce. Possibly the trade, if desired, would make them to order. There is an instrument, somewhat similar, the chondrometer, for estimating the quality of grain; only this is constructed upon the principle of the log; the leverage and counterpoise showing the weight of a pint, but indicating that of a bushel; as the half-minute sand-glass times the running out of the knots of the line, and indicates nautical miles. Goods-weighing-machines, at the railways, are on the steelyard, or shifting leverage principle; also the machines warranted to furnish you with "your correct weight."