_Sec. XIII. Of the Pulverization of Substances._ Various substances are employed either in grain, laminæ, filings, or impalpable powder. When treating of nitre, sulphur, and charcoal, and other bodies, we mentioned the processes for reducing them to powder. It will be sufficient here to remark, that cannon powder, when it is converted into fine powder, takes the name of meal-powder; the conversion being effected, by beating it in a leather sack, already described, by rolling it upon the mealing-table, or by the action of a wooden pestle in a mortar. It is then passed through a fine sieve. The sack is said to be a preferable mode, as nearly the whole of it becomes pulverized. Saltpetre, sulphur, charcoal, antimony, &c. may be reduced to powder in a mortar of cast-iron, marble, or wood. The best method of pulverizing saltpetre is given under that article, which consists in boiling it in a copper, and stirring it continually at the end of the process. The best mode of pulverizing, or bringing cast-iron to a state of fineness, is mentioned in the article on _Iron_. Some of the metals, as iron, zinc, the alloy of copper and zinc, (brass,) &c. are brought to a sufficient fineness by the file. The filings, if so required, may be afterwards sifted. Zinc, when in small pieces, may be pulverized, by means of a steel mortar and pestle. It may be granulated, by suffering it to run, when melted, through an iron cullender into water. For the pulverization of camphor, see that article. _Sec. XIV. Of Mixtures._ All compositions for fire-works, are generally made at first in mortars, and the mixture is then finished by passing it through a sieve; it being returned to the sieve, and again sifted. This operation is sometimes repeated several times. Of all compositions, that for sky-rockets requires to be most intimately blended. To receive the sifted matter, leather or parchment is used; but, in lieu of either, pasteboard, or several sheets of paper, cemented or glued together will answer. It is obvious, that, in preparing mixtures, of two, three, or four articles, they should not only be very fine, but uniformly and intimately mixed. Several receivers, made by stitching leather over a rim, in the manner of a sieve, would be found very convenient; but wooden bowls, and copper basins, are generally used. Some ingredients must be passed through a lawn sieve, after having been previously incorporated. A receiver, with a top, is the kind of sieve to be preferred. The composition for wheels, and common works, need not be so fine as for rockets. But in all fixed works, from which the fire is to play regularly, the ingredients must be very fine, and great care taken in mixing them together; and in those works, into the composition of which, iron and steel enter, the hands must neither touch them, nor moisture be suffered to come in contact. In either case, they would be apt to rust. PART III. FIRE-WORKS IN GENERAL. CHAPTER I.