Rockets of 10 or 11 lines are loaded with a composition containing 4 ounces of charcoal to a pound of powder. Rockets of from 7 to 9 lines are loaded with a composition having only 3 ounces of charcoal to a pound of powder, while rockets of 6 lines, or less, need only 2 ounces of charcoal to a pound of powder.
After the materials have been weighed, they are put through the coarsest horsehair screen three times, in order to mix them thoroughly. This is the only operation required in making the composition.
A composition that is too lively causes the rocket to burst, while if the charge is too light, or if the end is not carefully closed, the composition may be consumed without causing the rocket to ascend. Such a rocket is described as "breaking down." By this term the artificer describes the effect when the doubling over of the end of the case is not done with sufficient firmness. The result is a failure of solid resistance against the rush of gases.
The extreme of dryness is required for the rocket composition, both for the purposes of preservation and for effectiveness in discharging. If it becomes damp, the humidity causes the forming of spaces that admit too much fire, from which the bursting of the rocket is likely to result.
An exception should be noted in reference to Chinese fire. It is necessary to moisten the iron sand somewhat in order to secure the adherence of the sulphur to it. Details concerning the preparation of this composition are given under the heading of "Jets."