The usual precautions against fire and for storage of ordinary powder must be taken; and neither fuzes, caps, nor detonators of any kind should ever be allowed in the magazine containing the explosives. Dry guncotton should not be stored in the same magazine with wet guncotton. Before being placed in the magazine the boxes should be given a coat of paint or shellac, to protect them from moisture. They should also be placed on skids and the space between the skids partially filled with sawdust, to absorb any exuding nitro-glycerine. If any powder should be spilled on the floor, or nitro-glycerine exude and be absorbed by the sawdust, it should be removed at once and burned. The boxes should be turned over every month or two, and if kept long on hand they should be opened and the explosive tested from time to time.
When guncotton is received, pour into each package enough water to cover it, or otherwise immerse it. Let the water remain for 15 minutes; then pour it off and hermetically close the box. This should be done every three months.
Packages of guncotton stained brown or yellow, giving off nitric fumes, or showing other signs of decomposition, should be removed and immersed in water. If decomposition be far advanced, they should be removed to a safe place and burned.
WHERE AND HOW TO PLACE CHARGES.
Masonry or Brick Arch.—Attack the haunches of the arch or the piers. In bridges of a single arch the haunches are the best points, two trenches being dug across the width of the roadway down to the back of the arch. When there is no time for this, the charge should be placed along the crown of the arch. With guncotton untamped use ¾T2 × B; if tamped with a depth of earth equal to the thickness of the arch, use ⅜T2 × B.
With gunpowder, if over crown of arch, use 3/2T2 × B; if behind haunch, ⅔T2 × B. In the former case use tamping if possible equal to the thickness of the arch, and in the latter case equal to twice the thickness. The quantity of powder obtained by these rules should be divided into two or more charges placed across the arch.
When the bridge consists of a series of arches, and the piers are short and thick, the haunches should be attacked by the rules given in table on next page.
If the piers be high and thin, it is better to place the charges against them, as the fall of one pier will involve the destruction of two arches. The charge should be slightly greater than for a wall of the same thickness.
RULES FOR CALCULATING CHARGES FOR HASTY DEMOLITIONS BY GUNCOTTON OR GUNPOWDER.
Charges are in lbs.; B and T are in feet; t is in inches. B is length of breach to be made; T or t is thickness of object to be demolished.