Summurt.—There are very few compositions in which this is not required. In its usual marketable state, it is always sufficiently pure, and requires no examina tion; that is to say, when solid or in rolls. Pyrotech nists must be told that there is no difference between cast sulphur and flowers of sulphur; but as this latter is sometimes used from its being already powdered, it is proper they should know that it almost always contains a considerable proportion of sulphuric acid or oil of vitriol. If it is to be used, therefore, it should always be carefully washed; as this ingredient is not only injurious, from its moisture and property of ab sorbing water, but from its destroying the iron in those compounds into which this highly ornamental ingre dient enters. The perishable nature of all the iron fires must be attributed chiefly to this and the preceding species of neglect.
CHARCOAL.—In many fireworks this is an indispens able substance; in all cases indeed where iron is used, and where fires are acquired to be strong, or of a red colour. But it is subject to many variations of quality, not known to pyrotechnists, and which we shall there fore explain. It will be seen that an attention to these is of considerable importance ; but we consider it of DO moment how the charcoal is burnt, whether in pits or cylinders, provided it be completely deprived of all its volatile parts. All coals that contain much subcar bonate of potash, arc objectionable, for the very same reasons above assigned; namely, their property of ab sorbing water. They are easily examined by washing the powder in hot distilled water, and testing the solu tion with muriate of lime. That of litmus or turmeric is too delicate ; as these will show proportions of alkali that can be productive of no evil consequences. It
must next be recollected, that charcoal is required for two distinct purposes, force and ornament. For these two objects, different kinds are required. The greatest force is procured by the coals of soft wood, such as willow and alder ; and still more by that of the Rham nus frangula, or black dogwood. These, therefore, should always be used for sky rockets; in which force is essential, as conducing to high flights; and as far as a rocket composition includes mealed powder, such charcoal will be an ingredient. Those who are desirous of perfection, will use the same woods for the added charcoal. Where the object, on the contrary, is to ob tain common red fire, or burning sparks, the charcoal of hard wood is preferable. Still better is it, ,when, by being long ignited in close vessels, it acquires an extreme . degree of hardness; as it not only burns brighter, but is thrown out in larger sparks, from its greater power of resisting the force with which the compositions are driven. For the same reason, char coal for these purposes ought to be coarsely powdered, and the larger parts separated for use; whereas in the case of compounds, where strength alone is wanted, it cannot be too fine. As far as sky rockets are wanted for purposes purely ornamental, they thus require coarse charcoal. Lastly, there are some varieties of charcoal which have the property of producing compound sparks, not unlike those generated by iron ; or the original spark bursts after the first explosion, so as to throw out stars of light. The bark of the oak furnishes this kind of coal ; which may also be procured from mahogany and other hard woods of hot climates.