The proper charge of powder for the cannon, is divided into two unequal portions, the lesser of which is placed in the gun as a charge; the ball is placed on it in the usual way, and the rest of the powder (by much the greater portion,) placed over the ball, the lesser quantity being not more than a twelfth part of the whole. A cannon, so charged, will not project the ball more than 20 yards, where it might be caught with safety. Any person who has been in the custom of shooting, must have frequently observed, that when the shot happens to be mixed with the powder, its range is impeded; and, under similar circumstances, they have even been found only a few yards from the muzzle of the piece. This fact I have witnessed, although I confess I never once reflected on it. As to the explanation of this phenomenon, it appears, that it can only be accounted for by referring to the action of two opposite forces, mutually repelling each other, added to that of the charge under the ball; hence, the _reaction_ would be equal, if, under the same circumstances, both charges were alike situated: but the effect of the first charge is so much weakened by the counter effect of the second, that the projectile force of the ball becomes comparatively nothing. There is another trick very often performed, which, however chemical, is not looked upon in that light, neither do performers attempt to explain it; we mean the exhibition of the _Glace Inflammable_ of the French. The preparation is made in the following manner: melt some spermaceti over a fire, and add a sufficient quantity of spirit of turpentine, and blend them together. The mixture when cold, will become solid, having somewhat the appearance of ice. If made in hot weather, the vessel containing the melted substances must be immersed in cold water. It does not, we are told, remain in a solid state any length of time. It floats more or less in the fluid, which of course is the spirit of turpentine. The trick, with this preparation, after having put some of the solid and fluid substance together on a plate, is to pour upon it concentrated nitric acid, or a mixture of eight or ten parts of nitric acid, and two of sulphuric acid; inflammation ensues. It is no other in fact than accension of the oil of turpentine; the addition of the spermaceti is altogether secondary, and its effect, if any, must retard instead of promoting the combustion of the turpentine. The art of making this preparation is in rendering the essential oil solid and transparent, without altering its inflammable properties.