The spur-fire is so called, because its fire or sparks resemble the rowel of a spur. It is used in theatres and in rooms. It is the most beautiful of any yet known, and was invented by the Chinese, but greatly improved in Europe.
It requires great care to make it properly. Care ought to be taken that all the ingredients are of the best quality, that the lampblack is neither damp nor clodded, that the saltpetre is the best refined, and the sulphur perfectly pure. This composition is generally rammed into one or two ounce cases, about five or six inches long, but not driven very hard; and the cases must have their concave stroke struck very smooth, and the choak or vent not quite so large as the usual proportion: this charge, when driven, and kept a few months, will be much better than when rammed. If kept dry, it will last many years.
As the beauty of this composition cannot be seen at so great a distance as brilliant fire, it has a better effect in a theatre or room, than in the open air; and may be fired in a chamber, without danger. Its effect is of so innocent a nature, that it has been called cold fire; and so extraordinary is the fire produced from this composition, that if well made, the sparks will not burn a handkerchief when held in the midst of them. The hand, brought in contact with the spark, will feel only a sensation similar to that occasioned by the falling of rain. When any of these spurs are fired singly, they are called artificial fire-pots; but some of them, placed round a transparent pyramid of paper, and fired in a large room, make a very elegant appearance.
Composition of Spur-Fire.
| 1. | Saltpetre, | 4½ | lbs. |
| Sulphur, | 2 | lbs. | |
| Lampblack, | 1½ | lbs. or, | |
| 2. | Saltpetre, | 1 | lb. |
| Sulphur, | ½ | lb. | |
| Lampblack, | 4 | quarts. |
The saltpetre and sulphur must be first mixed together, and sifted, and then put into a marble mortar, and the lampblack with them, which are to be worked by degrees, with a wooden pestle, till all the ingredients appear of one colour, which will be a gray, approaching to black. It is then to be tried by driving a little of it into a case, and fired in a dark place; and if the sparks, which are called stars, or pinks, come out in clusters, and afterwards spread well, without any other sparks, it is a criterion of its goodness. If any drossy sparks appear, and the stars are not full, it is then not mixed sufficiently: but, if the pinks are very small, and soon break, it is a proof that it has been rubbed too much; for, in this case, few stars will appear. When, on the contrary, the mixture is not rubbed sufficiently, the combustion will be too weak, and lumps, resembling dross, with an obscure smoke, but without stars, will be emitted.
The peculiar effect of this composition is owing to the carbon of the lampblack, one part of which is inflamed, its combustion being supported by the oxygen gas of the atmosphere.
Sec. XI. Of the coloured Flame of Alcohol.
We have already remarked, in treating of alcohol, that its flame may be changed of various colours, by using certain native substances. See [Alcohol.]
Alcohol, thus mixed, or combined with substances, may be exhibited on certain occasions; for even cotton, when immersed in it, and set on fire, will show the same appearances. Morel remarks, that, if vinegar, a small portion of crude tartar, and common salt, and a still smaller quantity of saltpetre, be mixed together, and distilled, a liquid will be obtained, which burns with great brilliancy. It is doubtful, however, if we judge from analogy, whether either tartar, the salt, or saltpetre, will communicate any peculiar property to the distilled vinegar; for these saline substances will remain unaltered in the distilling vessel. The vinegar, nevertheless, may be obtained in a more concentrated state, being deprived of its colouring and other matter, and the greater part of its water, and, therefore, approach to the state of acetic acid.