The ordinary sulphur of commerce will serve, and the yellower it is the better. If impurities are contained in it, it should be melted and strained through a cloth. It must not be applied until after it has been reduced to a powder, such as is given by a silk screen of the smallest mesh.
The sulphur adds force to the mixture of saltpeter and charcoal up to a certain point. Beyond this point, however, it weakens the compositions into which it enters, serving only to make them burn more slowly and to give to the fire a color especially clear and luminous. It is to be observed that this augmentation of force from the introduction of sulphur takes place only when a small quantity is used. Examples are afforded by ordinary powder and by the composition with which rockets are loaded. In rockets having a diameter of 12 lines or less the composition will have inferior effectiveness if the sulphur be omitted. On the contrary, the composition will be stronger without sulphur when the rockets exceed 12 lines in diameter. And this force will always continue to increase as the diameter of the rocket increases, being steadfastly superior to that of the composition containing sulphur.