Page:Pyrotechnics the history and art of firework making (1922).djvu/171

 rounded ends, the shorter tool having a peg projecting which is equal in diameter to the bore of the choke. The tools are of such length that when they are inserted the peg takes up the position where the choke is to be formed. The case is then constricted at this point by a strong pressure with a stout cord wound round the case and soaped to allow it to slip round easily.

The case is then dried and charged by placing on a "spindle," which is a strong gun-metal base with a nipple fitting into the vent of the rocket and having a tapering spindle which fits tightly in the choke and projects up into the bore of the rocket. The composition is poured in in small quantities measured in a scoop, each scoopful being consolidated by blows with a wooden mallet or a wooden "drift" hollowed to take the spindle. Before the first scoop of composition is introduced, the rocket is "set down," that is, several blows are given on the drift to consolidate the paper at the choke and give it accurate shape. Next, a scoop of ground dry clay is poured in and charged firm as a protection to the paper of the choke. The charging is then proceeded with as detailed above. Varying drifts are used in order that the hole may approximately correspond with the diameter of the tapering spindle as the composition rises in the case.

A short portion of the case above the spindle is charged solid; this is referred to as the "heading," and is usually about one and a half times the bore in depth.

Large rockets are charged in a mould which fits tightly round the outside of the case and prevents the case being split under the pressure of the blows whilst being charged.

In early times these moulds were used for all sizes and were of cast metal, and it is from them that the classification of the sizes is derived. Rockets are designated by the weight of a ball of lead which fits the bore of the corresponding mould.