The magazine is a place of deposite for gunpowder, to preserve it from fire, and moisture. We have already mentioned the preservation of gunpowder in the article on that subject; but it may not be improper to offer some remarks, respecting the construction of magazines.
Authors differ in opinion, both in regard to their situation and construction; but they all agree, that they ought to be arched, and bomb-proof. The first powder magazines were made with gothic arches: Vauban constructed them in a semicircular form, to make them stronger. Their dimensions were, sixty feet long, within, and twenty-five broad. The foundations were eight or nine feet thick, and eight feet high, to the spring of the arch. The floors were two feet from the ground, for the purpose of keeping the magazine free from dampness.
It is observed, that the centres of semicircular arches will settle at the crown, and their sinking must break the cement. A remedy was applied for this inconvenience, by the arch of equilibration, as described in Hutton's work on bridges. As, in powder magazines, the ill effect of the breaking of the cement is particularly felt, Mr. Hutton proposed to find an arch of equilibration for them in particular, and to construct it, when the span is twenty feet, the pitch or height, ten, (which are the same dimensions as the semicircle), the inclined exterior walls at top, forming an angle of 113 degrees, and the height of their angular point, above the top of the arch, equal to seven feet.
A wall built round a magazine, gives it an additional security. The roof should be slated, or covered with lead or copper, and it ought to be furnished with a lightning rod, placed ten or fifteen yards from the building. The points of the rods may be either gilt, or of solid gold. Silver, however, is generally used; but, above all, platinum is to be preferred. The advantage of these points is, that they do not rust like iron, or become oxidized, an occurrence which would diminish their powers as conductors of the electric fluid.
To prevent the access of moisture, or rather to absorb it, some have recommended the inner walls to be covered with a composition of powdered coal, &c. Lining of magazines with sheet lead, appears to have some advantages.
St. Pierre observes, that a Prussian officer informed him, that, having remarked that vapour was attracted by lead, he had employed it for drying the atmosphere of a powder magazine, constructed under ground, in the throat of a bastion, rendered useless from its humidity. He ordered the concave ceiling of the arch to be lined with lead, where the gunpowder was deposited in barrels: the vapour of the wall collected in drops on the leaden roof, ran off, and left the gunpowder barrels perfectly dry.
Sec. III. Of the Driving or Ramming of Sky-rockets.
We purpose in the present article to give some general directions for the driving of rockets.