4. A body urged by two distinct forces in two different directions, will in any given time be found at the point where two lines meet that are drawn parallel to these directions, and through the points to which the body could have moved in the same time, had these forces acted separately.
5. The velocities of bodies, which by the action of gravity begin to fall from the rest, are in the same proportion as the times from their beginning of their falling.
6. The spaces run through by the descent of a body which began to fall from rest, are as the squares of the times, from the beginning of the fall.
7. The motion of a military projectile is in a curve.
Gun-powder, a composition of nitre, sulphur, and charcoal, well mixed together and granulated, which easily takes fire, and expands with amazing force, being one of the strongest propellents known.
Gun-powder.—Proportions of the different ingredients for making gunpowder, by different powers in Europe:
| Eng. | Fran. | Sweden. | Poland. | Italy. | Russia. | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Nitre | 75 | 75 | 75 | 80 | 76 | ¹⁄₂ | 70 | |||||
| Sulphur | 10 | 9 | ¹⁄₂ | 9 | 8 | 12 | ¹⁄₂ | 11 | ¹⁄₂ | |||
| Charcoal | 15 | 15 | ¹⁄₂ | 16 | 12 | 12 | ¹⁄₂ | 18 | ¹⁄₂ | |||
| Pounds | 100 | 100 | 100 | 100 | 100 | 100 | ||||||
Gunpowder. This well known powder is composed of seventy five parts, by weight, of nitre, sixteen of charcoal, and nine of sulphur, intimately blended together by long pounding in wooden mortars, with a small quantity of water. This proportion of the materials is the most effectual. But the variations of strength in different samples of gunpowder are generally occasioned by the more or less intimate division and mixture of the parts. The reason of this may be easily deduced from the consideration, that nitre does not detonate until in contact with inflammable matter; whence the whole detonation will be more speedy, the more numerous the surfaces of the contact. The same cause demands, that the ingredients should be very pure, because the mixture of foreign matter not only diminishes the quantity of effective ingredients which it represents, but likewise prevents the contacts by its interposition.
The nitre of the third boiling is usually chosen for making gunpowder, and the charcoal of light woods is preferred to that of those which are heavier, most probably because this last, being harder, is less pulverable. An improvement in the method of making the charcoal has lately been adopted, which consists in putting the wood, cut into pieces about nine inches long, into an iron cylinder laid horizontally, closed at one end, and furnished with small pipes at the other, that the pyroligneous acid and carburetted hidrogen may escape, and thus exposed to the heat of a fire made underneath. It is said, this charcoal improves the strength of gunpowder so much, that only two thirds of the old charge of gunpowder for ordnance are now used in our navy. The requisite pounding of the materials is performed in the large way by a mill, in which wooden mortars are disposed in rows, and in each of which a pestle is moved by the arbor of a water-wheel: it is necessary to moisten the mixture from time to time with water, which serves to prevent its being dissipated in the pulverulent form, and likewise obviates the danger of explosion from the heat occasioned by the blows. Twelve hours pounding is in general required to complete the mixture; and when this is done, the gunpowder is in fact made, and only requires to be dried to render it fit for use.
Proofs of powder.—The first examination of powder in the British mills, is by rubbing it in the hands to find whether it contains any irregular hard lumps. The second is by blasting 2 drams of each sort on a copper plate, and in this comparing it with an approved powder; in this proof it should nor emit any sparks, nor leave any beads or foulness on the copper. It is then compared with an approved powder, in projecting an iron ball of 64 lbs. from an 8 inch mortar, with a charge of 2 ounces. The best cylinder powder generally gives about 180 feet range, and pit 150; but the weakest powder, or powder that has been redried, &c. only from 107 to 117 feet.