Nitro Explosives: A Practical Treatise by P. Gerald Sanford

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~Calculation of the Volume of Gas Evolved in an Explosive Reaction.~--The
volume of gas evolved in an explosive reaction may be calculated, but only
when they are simple and stable products, such calculations being made at
0 deg. and 760 mm. Let it be required, for example, to determine the volume of
gas evolved by 1 gram-molecule of nitro-glycerine. The explosive reaction
of nitro-glycerine may be represented by the equation.

C_{3}H_{5}O_{3}(NO_{2})_{3} = 3CO_{2} + 2-1/2H_{2}O + 1-1/2N_{2} + 1/4O_{2}
By weight 227 = 132 + 45 + 42 + 8
By volume 2 = 3 + 2-1/2 + 1-1/2 + 1/4

The weights of the several products of the above reactions are calculated
by multiplying their specific gravities by the weight of 1 litre of
hydrogen at 0 deg. C. and 760 mm. (0.0896 grm). Thus,

One litre of CO_{2} = 22 x .0896 = 1.9712 grm.
" H_{2}O = 9 x " = 0.8064 "
" N_{2} = 14 x " = 1.2544 "
" O_{2} = 16 x " = 1.4336 "

The volume of permanent gases at 0 deg. and 760 mm. is constant, and assuming
the gramme as the unit of mass, is found to be 22.32 litres. Thus:--

Volume of 44 of CO_{2}, at 0 deg. and 760 mm. = 44/1.9712 = 22.32 litres.
18 " H_{2}O " " = 18/0.8044 = 22.32 "
28 " N_{2} " " = 28/1.2544 = 22.32 "
32 " O_{2} " " = 32/1.4366 = 22.32 "

Therefore

132 grms. of CO_{2} at 0 deg. C and 760 mm. = 22.32 x 3 = 66.96 litres.
45 " H_{2}O " " = 22.32 x 2-1/2 = 55.80 "
42 " N_{2} " " = 22.32 x 1-1/2 = 33.48 "
8 " O_{2} " " = 22.32 x 1/4 = 5.58 "
____________

161.82 "
Therefore 1 gram-molecule or 227 grms. of nitro-glycerine when exploded,
produces 161.82 litres of gas at 0 deg. C and 760 mm.

To determine the volume of gas at the temperature of explosion, we simply
apply the law of Charles.[A] Thus--

V : V' :: T : T' or V' = VT'/T

in which V represents the original volume.
V' " new volume.
T " original temperature on the absolute scale.
T' " new temperature of the same scale
In the present case T' = 6001 deg..

Therefore substituting, we have

V' = 161.82x6001/273 = 3557 litres

or at the temperature of explosion 1 gram-molecule of nitro-glycerine
produces 3,557 litres of permanent gas.

[Footnote A: According to the law of Charles, the volume of any gas varies
directly as its temperature on the absolute scale, provided the pressure
remains constant. Knowing the temperature on the centigrade scale, the
corresponding temperature on the absolute scale is obtained by adding 273
to the degrees centigrade.]

~Pressure or Crusher Gauge.~--There are many forms of this instrument. As
long ago as 1792 Count Rumford used a pressure gauge. The so-called
crusher gauge was, however, first used by Captain Sir Andrew Noble in his
researches on powder. Other forms are the Rodman[A] punch Uchatius
Eprouvette, and the crusher gauge of the English Commission on Explosives.
They are all based either upon the size of an indent made upon a copper
disc by a steel punch fitted to a piston, acted upon by the gases of the
explosive, or upon the crushing or flattening of copper or lead cylinders.

[Footnote A: Invented by General Rodman, United States Engineers.]

[Illustration: FIG. 55.--PRESSURE GAUGE.]

Berthelot uses a cylinder of copper, as also did the English Commission,
but in the simpler form of apparatus mostly used by manufacturers lead
cylinders are used. This form of apparatus (Fig. 55) consists of a base of
iron to which four uprights _a_ are fixed, set round the circumference of
a 4-inch circle; the lead plug rests upon the steel base let into the
solid iron block. A ring _c_ holds the uprights _d_ together at the top.
The piston _b_, which rests upon the lead plug, is a cylinder of tempered
steel 4 inches in diameter and 5 inches in length; it is turned away at
the sides to lighten it as much as possible. It should move freely between
the uprights _d_. In the top of this cylinder is a cavity to hold the
charge of explosive. The weight of this piston is 12-1/4 lbs. The shot _e_
is of tempered steel, and 4 inches in diameter and 10 inches in length,
and weighs 34-1/2 lbs. It is bored through its axis to receive a capped
fuse.

The instrument is used in the following manner:--A plug of lead 1 inch
long and 1 inch in diameter, and of a cylindrical form, is placed upon the
steel plate between the uprights _a_, the piston placed upon it, the
carefully weighed explosive placed in the cavity, and the shot lowered
gently upon the piston. A piece of fuse, with a detonator fixed at one
end, is then pushed through the hole in the shot until it reaches the
explosive contained in the cavity in the piston. The fuse is lighted. When
the charge is exploded, the shot is thrown out, and the lead cylinder is
more or less compressed. The lead plugs must be of a uniform density and
homogeneous structure, and should be cut from lead rods that have been
drawn, and not cast separately from small masses of metal.

[Illustration: FIG. 56.--_b_, STEEL PUNCH; _c_, LEAD CYLINDER FOR USE WITH
PRESSURE GAUGE.]

The strength of the explosive is proportional to the work performed in
reducing the height of the lead (or copper) plug, and to get an expression
for the work done it is necessary to find the number of foot-pounds (or
kilogrammetres) required to produce the different amounts of compression.
This is done by submitting exactly similar cylinders of lead to a crushing
under weights acting without initial velocity, and measuring the reduced
heights of the cylinders; from these results a table is constructed
establishing empirical relations between the reduced heights and the
corresponding weights; the cylinders are measured both before and after
insertion in the pressure gauge by means of an instrument known as the
micrometer calipers (Fig. 57).[A]

[Footnote A: An instrument called a "Foot-pounds Machine" has been
invented by Lieut. Quinan, U.S. Army. It consists of three boards,
connected so as to form a slide 16 feet high, in which a weight (the shot
of the pressure gauge) can fall freely. One of the boards is graduated
into feet and half feet. The horizontal board at the bottom, upon which
the others are nailed, rests upon a heavy post set deep in the ground,
upon which is placed the piston of the gauge, which in this case serves as
an anvil on which to place the lead cylinders. The shot is raised by means
of a pulley, fixed at the top of the structure, to any desired height, and
let go by releasing the clutch that holds it. The difference between the
original length and the reduced length gives the compression caused by the
blow of the shot in falling, and gives the value in foot-pounds required
to produce the different amounts of compression. (Vide _Jour. U.S. Naval
Inst._, 1892.)]

[Illustration: FIG. 57.--MICROMETER CALIPERS FOR MEASURING DIAMETER OF
LEAD CYLINDERS.]

~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.

[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 cylinder and against
the plug, and so effectually prevents any escape. In the firing plug F is
a conical hole closed by a cone fitting with great exactness, which, when
the vessel is prepared for firing, is covered with fine tissue paper to
act as an insulator. The two firing wires GG, one in the insulated cone,
the other in the firing plug, are connected by a very fine platinum wire
passing through a glass tube filled with meal powder. The wire becomes
red-hot when connection is made with a Leclanche battery, and the charge
which has previously been inserted into the vessel is fired. The crusher
plug is fitted with a crusher gauge H for determining the pressure of the
gases at the moment of explosion, and in addition there is frequently a
second crusher gauge apparatus screwed into the cylinder. When it is
desired to allow the gases to escape for examination, the screw J is
slightly withdrawn. The gases then pass into the passage I, and can be led
to suitable apparatus in which their volume can be measured, or in which
they can be sealed for subsequent chemical analysis.

The greatest care must be exercised in carrying out experiments with this
apparatus; it is particularly necessary to be sure that all the joints are
perfectly tight before exploding the charge. Should this not be the case,
the gases upon their generation will cut their way out, or completely blow
out the part improperly secured, in either case destroying the apparatus.
The effect produced upon the apparatus when the gas has escaped by cutting
a passage for itself is very curious. The surface of the metal where the
escape occurred presents the appearance of having been washed away in a
state of fusion by the rush of the highly heated products.

~The Pressure Gauge.~--The pressure is found by the use of a little
instrument known as the pressure gauge which consists of a small chamber
formed of steel, inside of which is a copper cylinder, and the entrance
being closed by a screw gland, in which a piston, having a definite
sectional area, works. There is a gas check E (Fig. 60) placed in the
gland, and over the piston, which prevents the admission of gas to the
chamber. When it is desired to find the pressure in the chamber of a gun,
one or more of these crushers are made up with or inserted at the extreme
rear end of the cartridge, in order to avoid their being blown out of the
gun when fired. This, however, often takes place, in which case the gauges
are usually found a few yards in front of the muzzle. The copper cylinders
which register the pressure are made 0.5 inch long from specially selected
copper, the diameters being regulated to give a sectional area of either
1/12 or 1/24 square inch.

[Illustration: FIG. 60.--CRUSHER GAUGE. _E_, GAS CHECK.]

Hollow copper cylinders are manufactured with reduced sectional areas for
measuring very small pressures. It has been found that these copper
cylinders are compressed to definite lengths for certain pressures with
remarkable uniformity. Thus a copper cylinder having a sectional area of
1/12 square inch, and originally 1/2 inch long, is crushed to a length of
0.42 inch by a pressure of 10 tons per square inch. By subsequently
applying a pressure of 12 tons per square inch the cylinder is reduced to
a length of 0.393 inch. Before using the cylinders, whether for
experimenting with closed vessels or with guns, it is advisable to first
crush them by a pressure a little under that expected in the experiment.
Captain Sir A. Noble used in his experiments a modification of Rodman's
gauge. (Ordnance Dept., U.S.A., 1861.)

~By Calculation.~--To calculate the pressure developed by the explosion of
dynamite in a bore-hole 3 centimetres in diameter, charged with 1
kilogramme of 75 per cent. dynamite, Messrs Vieille and Sarrau employ the
following formula:--

P = V_{o}(1 + Q/273._c_)/(V - _v_).

Where V_{o} = the volume (reduced to 0 deg. and 760 mm.) of the gases produced
by a unit of weight of the explosive; Q the number of calories disengaged
by a unit of weight of the explosive; _c_ equals the specific heat at
constant volume of the gases; V the volume in cubic centimetres of a unit
of weight of the explosive; _v_ the volume occupied by the inert
materials of the explosive. The volume of gas produced by the explosion of
1 kilogramme of nitro-glycerine (at 0 deg. and 760 mm.) is 467 litres.

V_{o} will therefore equal 0.75 x 467 = 350.25.

The specific heat _c_ is, according to Sarrau, .220 (_c_); and according
to Bunsen, 1 kilogramme of dynamite No. 1 disengages 1,290 (Q) calories.
The density of dynamite is equal to 1.5, therefore

V = 1/1.5 = .666.

If we take the volume of the kieselguhr as .1, we find from above formula
that

P = 350(1 + 1290/(273 x .222))/(.600 - .1) = 13,900 atmospheres,

which is equal to 14,317 kilogrammes per square centimetre. The pressure
developed by 1 kilogramme of pure nitro-glycerine equals 18,533
atmospheres, equals 19,151 kilogrammes. Applying this formula to gun-
cotton, and taking after Berthelot, Q = 1075, and after Vieille and
Sarrau, V_{o} = 671 litres, and _c_ as .2314, and the density of the
nitro-cellulose as 1.5, we have (V = O)

P = 671(1 + 1075/(273 x .2314))/.666 = 18,135 atmospheres.

To convert this into pressure of kilogrammes per square centimetre, it is
necessary to multiply it by the weight of a column of mercury 0.760 m.
high, and 1 square centimetre in section, which is equal to increasing it
by 1/30. It thus becomes

P^{k} = (1 + 1/30).

P^{k} = 18,135 x 1.033 = 18,733 kilogrammes.

The following tables, taken from Messrs William Macnab's and E. Ristori's
paper (_Proc. Roy. Soc._, 56, 8-19), "Researches on Modern Explosives,"
are very interesting. They record the results of a large number of
experiments made to determine the amount of heat evolved, and the quantity
and composition of the gases produced when certain explosives and various
smokeless powders were fired in a closed vessel from which the air had
been previously exhausted. The explosions were carried out in a
"calorimetric bomb" of Berthelot's pattern.[A]

[Footnote A: For description of "bomb," see "Explosives and their Power,"
Berthelot, trans. by Hake and Macnab, p. 150. (Murray.)]

Table Showing Quantity of Heat and Volume and Analysis of Gas Developed
per Gramme with Different Sporting and Military Smokeless Powders Now In
Use

______________________________________________________________________
| | | | |
Name of Explosive. | Calories | Permanent | Aqueous | Total Volume |
| per grm. | Gases. | Vapour. | of Gas at 0 deg. |
| | | | and 760 mm. |
______________________|__________|___________|_________|______________|
| | cc/grm | cc/grm | cc/grm |
E.C. powder, English | 800 | 420 | 154 | 574 |
S.S. powder | 799 | 584 | 150 | 734 |
Troisdorf, German | 943 | 700 | 195 | 895 |
Rifleite, English | 864 | 766 | 159 | 925 |
B.N., French | 833 | 738 | 168 | 906 |
Cordite, English | 1253 | 647 | 235 | 882 |
Ballistite, German | 1291 | 591 | 231 | 822 |
Ballistite, Italian | 1317 | 58l | 245 | 826 |
and Spanish | | | | |
______________________|__________|___________|_________|______________|

The figures in column headed "Co-efficient of Potential Energy" serve as a
measure of comparison of the power of the explosives, and are the products
of the number of calories by the volume of gas, the last three figures
being suppressed in order to simplify the results.

The amounts of water found were calculated for comparison as volumes of
H_{2}O gas at 0 deg. and 760 mm.

E.C. powder consists principally of nitro-cellulose mixed with barium
nitrate and a small proportion of camphor.

S.S. of nitro-lignine mixed with barium nitrate and nitro-benzene.

Troisdorf powder is gelatinised nitro-cellulose; rifleite gelatinised
nitro-cellulose and nitro-benzene.

Cordite contains 58 per cent. nitro-glycerine, 37 per cent. gun-cotton,
and 5 per cent. vaseline.

Ballistite (Italian) consists of equal parts nitro-cellulose and nitro-
glycerine, and 1/2 per cent. of aniline. The German contains a higher
percentage of nitro-cellulose.

TABLE SHOWING THE HEAT DEVELOPED BY EXPLOSIVES CONTAINING NITRO-GLYCERINE
AND NITRO-CELLULOSE IN DIFFERENT PROPORTIONS.

______________________________________________________________________
Composition of Explosives. | Calories per cent.
_____________________________________________|________________________
Nitro-cellulose | |
(N = 13.3 per cent.). | Nitro-glycerine. |
| |
100 per cent. dry pulp | 0 | 1061
100 " gelatinised | 0 | 922
90 " | 10 per cent. | 1044
80 " | 20 " | 1159
70 " | 30 " | 1267
60 " | 40 " | 1347
50 " | 50 " | 1410
40 " | 60 " | 1467
0 " | 100 " | 1652
__________________________|__________________|________________________
| |
Nitro-cellulose | |
(N=12.24 per cent.) | Nitro-glycerine. |
| |
80 per cent. | 20 per cent. | 1062
60 " | 40 " | 1288
50 " | 50 " | 1349
40 " | 60 " | 1405
| |
__________________________|__________________|________________________|
Nitro-cellulose | |
(N = 13.3 per cent.). | Nitro-glycerine. | Vaseline.
| |
55 per cent. | 40 per cent. | 5 per cent. 1134
35 " | 60 " | 5 " 1280
__________________________|__________________|________________________

TABLE OF RESULTS OBTAINED BY LIEUT. W. WALKE., OF THE ARTILLERY, U.S.A,
WITH QUINAN'S PRESSURE GAUGE.

Nitro-glycerine being taken as 100. (From _U.S. Naval Inst. Jour._)

__________________________________________________________________________
| | |
| Compression | Order of |
Name of Explosive. | of Lead | Strength. |
| | |
| Inch. | |
Explosive gelatine | 0.585 | 106.17 |
Hellhoffite | 0.585 | 106.17 |
Nitro-glycerine | 0.551 | 100.00 | Standard, N.G.
Nobel's smokeless powder | 0.509 | 92.38 |
Nitro-glycerine | 0.509 | 92.37 |
Gun-cotton | 0.458 | 83.12 | U.S. naval torpedo
| | | gun-cotton
Gun-cotton | 0.458 | 83.12 | Stowmarket.
Nitro-glycerine | 0.451 | 81.85 | Vouges, N.G.
Gun-cotton | 0.448 | 81.31 |
Dynamite No. 1 | 0.448 | 81.31 |
Dynamite de Traul | 0.437 | 79.31 |
Emmensite | 0.429 | 77.86 |
Amide powder | 0.385 | 69.87 |
Oxonite | 0.383 | 69.51 |
Tonite | 0.376 | 68.24 | G.C. 52.5%, and
| | | Ba(NO_{3})_{2}, 47.5%
Bellite | 0.362 | 65.70 |
Rack-a-rock | 0.340 | 61.71 |
Atlas powder | 0.333 | 60.43 |
Ammonia dynamite | 0.332 | 60.25 |
Volney's powder No. 1 | 0.322 | 58.44 | Nitrated naphthalene.
" No. 2 | 0.294 | 53.18 | " "
Melinite | 0.280 | 50.82 | Picric acid 70%, and
| | | sol. nitro-cotton 30%.
Silver fulminate | 0.277 | 50.27 |
Mercury | 0.275 | 49.91 |
Mortar powder | 0.155 | 28.13 |
_________________________|_____________|___________|______________________

~Composition of some of the Explosives in Common Use.~

~Ordinary Dynamite.~

Nitro-Glycerine 75 per cent.
Kieselguhr 25 "

~Amvis.~

Nitrate of Ammonia 90 per cent.
Chloro-di-nitro Benzene 5 "
Wood Pulp 5 "

~Ammonia Nitrate Powder.~

Nitrate of Ammonia 80 per cent.
Chlorate of Potash 5 "
Nitro-Glucose 10 "
Coal Tar 5 "

~Celtite.~

Nitro-Glycerine 56-59 parts.
Nitro-Cotton 2-3.5 "
KNO_{3} 17-21 "
Wood Meal 8-9 "
Ammonium Oxalate 11-13 "
Moisture 0.5-1.5 "

~Atlas Powders.~

Sodium Nitrate 2.0 per cent.
Nitro-Glycerine 75.0 "
Wood Pulp 21.0 "
Magnesium Carbonate 2.0 "

~Dauline.~

Nitro-Glycerine 50 per cent.
Sawdust 30 "
Nitrate of Potash 20 "

~Vulcan Powder.~

Nitro-Glycerine 30 per cent.
Nitrate of Soda 52.5 "
Sulphur 7.0 "
Charcoal 10.5 "

~Vigorite.~

Nitro-Glycerine 30 per cent.
Nitrate of Soda 60 "
Charcoal 5 "
Sawdust 5 "

~Rendrock.~

Nitrate of Potash 40 per cent.
Nitro-Glycerine 40 "
Wood Pulp 13 "
Paraffin or Pitch 7 "

~Ammonia Nitrate Powder.~

Ammonia Nitrate 80 per cent.
Potassium Chlorate 5 "
Nitro-Glucose 10 "
Coal Tar 5 "

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