The case forming the fire pot is closed at the bottom by a wooden disk fastened with glue. This disk ends in a screw.
Its diameter is that of the pot into which it enters, and its thickness is at least 6 lines. It has a shoulder of which the breadth is equal to the thickness of the wall of the case that is to be placed on it. The disk and screw are pierced in the direction of their length with a hole 2 1/2 lines in diameter. (PL X, figs. 15,16,17, and 18.)
The diameter of the case should be proportioned to the size of the seven serpents with which it is to be garnished. Seven are usually employed, since that number may be easily arranged in a circle. The height of the case is from six to seven times its interior diameter.
In arranging the garniture, a beginning is made by passing a match end through the hole that traverses the disk and screw. The match extends onward within the case about an inch, to a distance 5 or 6 lines beyond the end of the screw, where it is held in position by priming paste. (PL X, fig. 15.)
The worker next takes as many squares of paper as there are pots to garnish, from which to fashion what is called the powder bags. These are placed on the end of the stick that has been employed for molding the pots, and, by rolling, the squares of paper are made to take a cylindrical form. (PL X, fig. 18.)
A measure of the composition is placed in each of these papers. The portion for each should be one-seventh of the garniture's total weight. Two match ends are also placed in each, of sufficient length to reach an inch beyond the point at which the neck of the powder bag is to be tied. The bag is now closed at the top, and a string is tied about it. Care must be taken to preserve the round shape throughout the length of the paper sack, and the excess of paper beyond the ligature is cut off with scissors.
The mixture employed contains about 4 ounces of charcoal to a pound of powder.
The charge having been made ready and the pot primed, a little powder is scattered within, and the powder sack is then placed inside with the ligature downward. The bag is pushed to the bottom of the pot by means of the molding stick. The charge is next pierced with seven or eight awl holes. Another pinch of powder is scattered over the bag.
The garniture is now set in place, and, lest it should be shaken about, it is fixed in position by wadding made from torn bits of paper. The pot is then closed with a disk of heavy paper, snipped around the edges, which is firmly pasted in place. Finally, a band of paper is pasted about the cylinder, covering the bent-down portion of the disk. The pot thus prepared is ready to be screwed on the brin. This is the name given by the artificers to a wooden bar prepared for holding a series of pots.
The brin has commonly a length of 8 feet, a width of 2 1/2 inches and a thickness of 1 1/2 inches. It is pierced with screw holes, in order to receive the screws of the fire pots, and these holes are sufficiently near one another so that only 3 or 4 lines of distance intervene between each two pots. (PL X, fig. 15.)
As the screw holes do not extend through the brin, the artificer, reversing the bar, shapes on the underside a groove 3 lines in width and 3 lines in depth, in which are made small holes of from 2 to 3 lines in diameter, reaching to the screw holes. A fuse is laid in this groove. It is fastened on each of the small holes with priming paste, and the whole is then covered over with a strip of pasted paper along the length of the groove.
The worker now returns the brin to its original position with the screw holes up. A pinch of powder is placed in each hole, and, by tapping, this is caused to fall into the small communicating hole underneath. The pots are now screwed in position, and the brin is ready to be fired. At the time of discharge, it is necessary to break one end of the paper covering on the underside of the brin, to expose an end of the match.
The effect of this firework is to discharge all of the pots at the same time, and thus "to embellish the air with a great quantity of very brilliant fires."