Page:Pyrotechnics the history and art of firework making (1922).djvu/170

 "rockette," from "rocca," the Italian word for a bobbin, a diminutive of distaff.

As a rocket is the most important unit in the art of pyrotechny, a description of its manufacture will assist in the consideration of a large number of other fireworks which are either modifications of or based upon the underlying principles of the rocket, as well as the several principles governing all fireworks.

The ingredients of rocket composition are those of gunpowder in approximately similar proportions, but the resultant composition is not gunpowder, the reason being that the ingredients are less intimately mixed, with the result that the combustion is spread over a longer interval of time. Instead of the whole mass deflagrating instantly, only the exposed surface is consumed. It is the recoil produced by the rush of gases, and partially consumed matter, from the violently burning composition which projects the rocket forward. The obvious form for the case containing the composition is cylindrical, both on account of ease of construction and of charging. In order to get the greatest possible reaction from the burning composition, the case of the rocket is constricted or choked, so that the fire may issue as it were in the form of a jet. This choke has one obvious disadvantage, it reduces the surface of composition to the area of the opening, thus restricting the initial burning surface at the time when the maximum of effort is required to force the rocket into motion. This defect is overcome by having a tapering hole up almost the entire length of the composition, thus giving a large burning surface with a consequent discharge of gas through a small orifice and a resultant powerful jet of fire and gas.

The rocket case is of stout paper rolled on a former consolidated by rolling under a board. The choke is formed by inserting into the bore of the rocket two wooden tools with