The Use of Lead Cylinders.—­The method of using lead cylinders to test the strength of an explosive is a very simple affair, and is conducted as follows:—­A solid cast lead cylinder, of any convenient size, is bored down the centre for some inches, generally until the bore-hole reaches to about the centre of the block.  The volume of this hole is then accurately measured by pouring water into it from a graduated measure, and its capacity in cubic centimetres noted.  The bore-hole is then emptied and dried, and a weighed quantity (say 10 grms.) of the explosive pressed well down to the bottom of the hole.  A hole is then made in the explosive (if dynamite) with a piece of clean and rounded glass rod, large enough to take the detonator.  A piece of fuse, fitted with a detonator, is then inserted into the explosive and lighted.  After the explosion a large pear-shaped cavity will be found to have been formed, the volume of which is then measured in the same way as before.

The results thus obtained are only relative, but are of considerable value for comparing dynamites among themselves (or gun-cottons).  Experiments in lead cylinders gave the relative values for nitro-glycerine 1.4, blasting gelatine 1.4, and dynamite 1.0. (Fig. 58 shows sections of lead cylinders before and after use.)

[Illustration:  FIG. 58.—­LEAD CYLINDERS BEFORE AND AFTER USE.]

Standard regulations for the preparation of lead cylinders may be found in the Chem.  Zeit., 1903, 27 [74], 898.  They were drawn up by the Fifth International Congress of App.  Chem., Berlin.  The cylinder of lead should be 200 mm. in height and 200 mm. in diameter.  In its axis is a bore-hole, 125 mm. deep and 25 mm. in diameter.  The lead used must be pure and soft, and the cylinder used in a series of tests must be cast from the same melt.  The temperature of the cylinders should be 15 deg. to 20 deg. throughout.  Ten grms. of explosive should be used and wrapped in tin-foil.  A detonator with a charge of 2 grms., to be fired electrically, is placed in the midst of the explosive.  The cartridge is placed in the bore-hole, and gently pressed against the bottom, the firing wires being kept in central position.  The bore-hole is then filled with dry quartz sand, which must pass through a sieve of 144 meshes to the sq. cm., the wires being .35 mm. diameter.  The sand is filled in evenly, any excess being levelled off.  The charge thus prepared is then fired electrically.  The lead cylinder is then inverted, and any residues removed with a brush.  The number of c.c. of water required to fill the cavity, in excess of the original volume of the bore-hole, is a measure of the strength of the explosive.  The results are only comparable if made with the same class of explosive.  A result is to be the mean of at least three experiments.  The accuracy of the method depends on (a) the uniform temperature of the lead cylinder (15 deg. to 20 deg.  C. 7); (b) on the uniformity of the quartz sand; (c) on the uniformity of the measurements.