Pyrotechny in General.

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a few yards from the gun, although the report will be asgreat as if the charge and ball had been used in the usualmanner. This trick is often performed by jugglers, to thegreat astonishment of the spectators. The mode of catchinga cannon hall is also of the same character.

The proper charge of powder for the cannon, is dividedinto two unequal portions, the lesser of which is placed inthe gun as a charge; the ball is placed on it in the usualway, and the rest of the powder (by much the greater por-tion,) placed over the ball, the lesser quantity being notmore than a twelfth part of the whole. A cannon, so charged,will not project the ball more than 20 yards, where it mightbe caught with safety.

Any person who has been in the custom of shooting, musthave frequently observed, that when the shot happens to bemixed with the powder, its range is impeded; and, undersimilar circumstances, they have even been found only a fewyards from the muzzle of the piece. This fact 1 have wit-nessed, although I confess I never once reflected on it.

As to the explanation of this phenomenon, it appears, thatit can only be accounted for by referring to the action of twoopposite forces, mutually repelling each other, added to thatof the charge under the ball; hence, the reaction would beequal, if, under the same circumstances, both charges werealike situated: but the effect of the first charge is so muchweakened by the counter effect of the second, that the pro-jectile force of the ball becomes comparatively nothing.

There is another trick very often performed, which, how-ever chemical, is not looked upon in that light, neither doperformers attempt to explain it; we mean the exhibition ofthe Glace inflammable of the French .

The preparation is made in the following manner: meltsome spermaceti over a fire, and add a sufficient quantity ofspirit of turpentine, and blend them together. The mixturewhen cold, will become solid, having somewhat the appear-ance of ice. If made in hot weather, the vessel containingthe melted substances must be immersed in cold water. Itdoes not, we are told, remain in a solid state any length oftime.

It floats more or less in the fluid, which of course is thespirit of turpentine. The trick, with this preparation, afterhaving put some of the solid and fluid substance togetheron a plate, is to pour upon it concentrated nitric acid, or amixture of eight or ten parts of nitric acid, and two of sul-phuric acid; inflammation ensues. It is no other in fact than