GERBES.
Gerbes consist of strong cylindrical cases of thick paper, filled with brilliant composition, and sometimes with balls, or stars. Gerbes throw up into the air luminous and sparkling jets of fire; and when arranged in a circular manner, as the radii of a circle, they form what is called a fixed sun. The thickness of the cases for brilliant fire must be a fourth part of the diameter, and for Chinese fire a sixth part. The case is loaded on a nipple, having a point equal in length to the same diameter, and in thickness to a fourth part of it; but as it generally happens that the mouth of the jet becomes larger than is necessary for the effect of the fire, the case should be first charged by filling it to a height equal to a fourth part of the diameter, with clay, which must be rammed down. When the charge is completed with the composition, the case should be closed with a tompeon of wood, and then choked. The train, or match, must be of the same composition as that employed for loading, otherwise the jet would be subject to burst. Charged cases may be pierced with two holes near the neck, in order to have three jets; or, if a top pierced with a number of holes be added to them, they will imitate a bubbling fountain. Jets intended for representing sheets of fire ought not to be choked. They must be placed in a horizontal position, or inclining a little downwards.
Composition for Gerbes, or jets of fire.
Key:
S = Saltpetre.
P = Pulverized powder.
Su = Sulphur.
C = Charcoal.
| JETS. | S | P | Su | C | Iron sand, or filings. | |||||
| lb. | oz. | lb. | oz. | oz. | oz. | oz. | ||||
| ·4 of an inch or less interior diameter | { Chinese fire | 1 | 1 | 8 | 2 | |||||
| { White fire | 1 | 8 | 3 | 2 | Sand, 1st order | 8 | ||||
| ·5 to 1 inch diameter | { Brilliant fire | 1 | Filings | 5 | ||||||
| { White fire | 1 | 8 | 2 | |||||||
| { Chinese fire | 1 | 4 | 5 | 5 | Sand, 3rd order | 12 | ||||
| 1·1 to 1·5 diameter | { | 1 | 4 | 7 | 5 | Mixed sand | 12 | |||
| { | 1 | 8 | 5 | |||||||
| { | 2 | 2 | 8 | |||||||
The saltpetre, powder, and charcoal, are three times sifted through a hair sieve; the iron sand is besprinkled with sulphur, after being moistened with spirits of wine, that the sulphur may adhere to it, and they are then mixed together. The sulphuretted sand is then spread over the first mixture, and the whole is mixed with a ladle only, for if a sieve were employed, it would separate the sand from the other materials.
When sand larger than the 2nd order is used, the composition is moistened with spirits of wine, so that it forms itself into balls, and the jets are then loaded with them.
IRON FILINGS.
These filings must be quite clean, and free from rust. They must be thoroughly mixed with the compositions of which they form one of the ingredients; which, however, will not afterwards keep in good order longer than a week, as the moisture contracted by saltpetre rusts the filings, and destroys the effect they are intended to produce.
IRON SAND, OR POUNDED IRON.