tive 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.

[Illustration: FIG. 59.--NOBLE'S PRESSURE GAUGE.]

~Noble's Pressure Gauge.~--The original explosive vessels used by Captain
Sir A. Noble in his first experiments were practically exactly similar to
those that he now employs, which consists of a steel barrel A (Fig. 59),
open at both ends, which are closed by carefully fitted screw plugs,
furnished with steel gas checks to prevent any escape past the screw. The
action of the gas checks is exactly the same as the leathers used in
hydraulic presses. The pressure of the gas acting on both sides of the
annular space presses these sides firmly against the