The method of preparing a blasting charge is as follows:—­A piece of Bickford fuse of the required length is cut clean and is inserted into a detonator until it reaches the fulminate.  The upper portion of the detonator is then squeezed round the fuse with a pair of nippers.  The object of this is not only to secure that the full power of the detonator may be developed, but also to fix the fuse in the cap (Fig. 34).  When the detonator, &c., is to be used under water, or in a damp situation, grease or tallow should be placed round the junction of the cap with the fuse, in order to make a water-tight joint.  A cartridge is then opened and a hole made in its upper end, and the detonator pushed in nearly up to the top.  Gun-cotton or tonite cartridges generally have a hole already made in the end of the charge.  Small charges of dry gun-cotton, known as primers, are generally used to explode wet gun-cotton.  The detonators (which are often fired by electrical means) are placed inside these primers (Fig. 35).

[Illustration:  FIG. 35.  PRIMER.]

One of the forms of electric exploders used is shown in Fig. 36.  This apparatus is made by Messrs John Davis & Son, and is simply a small hand dynamo, capable of producing a current of electricity of high tension.  This firm are also makers of various forms of low tension exploders.  A charge having been prepared, as in Fig. 34, insert into the bore-hole one or more cartridges as judged necessary, and squeeze each one down separately with a wooden rammer, so as to leave no space round the charge, and above this insert the cartridge containing the fuse and detonator.  Now fill up the rest of the bore-hole with sand, gravel, water, or other tamping.  With gelatine dynamites a firm tamping may be used, but with ordinary dynamite loose sand is better.  The charge is now ready for firing.

[Illustration:  FIG. 36.—­ELECTRIC EXPLODER.]

CHAPTER VI.

SMOKELESS POWDERS.

Smokeless Powder in General—­Cordite—­Axite—­Ballistite—­U.S.  Naval
Powder—­Schultze’s E.G.  Powder—­Indurite—­Vielle Poudre—­Rifleite—­
Cannonite—­Walsrode—­Cooppal Powders—­Amberite—­Troisdorf—­Maximite—­
Picric Acid Powders, &c., &c.

The progress made in recent years in the manufacture of smokeless powders has been very great.  With a few exceptions, nearly all these powders are nitro compounds, and chiefly consist of some form of nitro-cellulose, either in the form of nitro-cotton or nitro-lignine; or else contain, in addition to the above, nitro-glycerine, with very often some such substance as camphor, which is used to reduce the sensitiveness of the explosive.  Other nitro bodies that are used, or have been proposed, are nitro-starch, nitro-jute, nitrated paper, nitro-benzene, di-nitro-benzene, mixed with a large number of other chemical substances, such as nitrates, chlorates, &c.  And lastly, there are the picrate powders, consisting of picric acid, either alone or mixed with other substances.