Nitro Explosives: A Practical Treatise by P. Gerald Sanford

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To sum up briefly the method of using the regulator:--Being filled with
mercury to about 1\2 inch below the T, attach the gas supply as in diagram
(Fig. 2), the brass tap being open, and the tube B unclosed by the
mercury. Allow the gas to completely expel the air in the apparatus. Push
down the tube A so that the end of B is well under the surface of the
mercury. Turn off the tap of the bye-pass until the smallest bead of flame
is visible. Raise A and B, and allow the temperature to rise until the
desired point is attained. Then push the tubes A and B slowly down until
the flame is just shut off. The regulator will then keep the temperature
at that point.

~Will's Test for Nitro-Cellulose.~--The principle of Dr W. Will's test[A]
may be briefly described as follows:--The regularity with which nitro-
cellulose decomposes under conditions admitting of the removal of the
products of decomposition immediately following their formation is a
measure of its stability. As decomposing agent a sufficiently high
temperature (135 deg. C.) is employed, the explosive being kept in a
constantly changing atmosphere of carbon dioxide, heated to the same
temperature: the oxides of nitrogen which result are swept over red-hot
copper, and are then reduced to nitrogen, and finally, the rates of
evolution of nitrogen are measured and compared. Dr Will considers that
the best definition and test of a stable nitro-cellulose is that it should
give off at a high temperature equal quantities of nitrogen in equal
times. For the purposes of manufacture, it is specially important that the
material should be purified to its limit, i.e., the point at which further
washing produces no further change in its speed of decomposition measured
in the manner described.

[Footnote A: W. Will, _Mitt. a. d. Centrallstelle f. Wissench. Techn.
Untersuchungen Nuo-Babelsberg Berlin_, 1902 [2], 5-24.]

The sample of gun-cotton (2.5 grms.) is packed into the decomposition tube
15 mm. wide and 10 cm. high, and heated by an oil bath to a constant
temperature, the oxides so produced are forced over ignited copper, where
they are reduced, and the nitrogen retained in the measuring tubes. Care
must be taken that the acid decomposition products do not condense in any
portion of the apparatus. The air in the whole apparatus is first
displaced by a stream of carbon dioxide issuing from a carbon dioxide
generator, or gas-holder, and passing through scrubbers, and this stream
of gas is maintained throughout the whole of the experiment, the gas being
absorbed at the end of the system by strong solution of caustic potash. To
guard against the danger of explosions, which occasionally occur, the
decomposition tube and oil bath are surrounded by a large casing with
walls composed of iron plate and strong glass.

Dr Will's apparatus has been modified by Dr Robertson,[A] of the Royal
Gunpowder Factory, Waltham Abbey. The form of the apparatus used by him is
shown in Fig. 51.

~CO_{2} Holders.~--Although objection has been taken to the use of
compressed CO_{2} in steel cylinders on account of the alleged large and
variable amount of air present, it has, nevertheless, been found possible
to obtain this gas with as little as 0.02 per cent. of air. Frequent
estimations of the air present in the CO_{2} of a cylinder show that even
with the commercial article, after the bulk of the CO_{2} has been
removed, the residual gas contains only a very small amount of air, which
decreases in a gradual and perfectly regular manner. For example, one
cylinder which gave 0.03 per cent. of air by volume, after three months'
constant use gave 0.02 per cent. The advantage of using CO_{2} from this
source is obvious when compared with the difficulty of evolving a stream
of gas of constant composition from a Kipps or Finkener apparatus. A
micrometer screw, in addition to the main valve of the CO_{2} cylinder, is
useful for governing the rate of flow. A blank experiment should be made
to ascertain the amount of air in the CO_{2} and the correction made in
the readings afterwards.

[Footnote A: _Jour. Soc. Chem. Ind._, June 30, 1902, p. 819.]

[Illustration: Fig 51.--Will's Apparatus for Testing Nitro-cellulose]

~Measurement of Pressure and Rate of Flow.~--Great attention is paid to
the measurement of the rate of flow of gas, which is arrived at by
counting with a stop-watch the number of bubbles of gas per minute in a
small sulphuric acid wash bottle. A mercury manometer is introduced here,
and is useful for detecting a leak in the apparatus. The rate of flow that
gives the most satisfactory results is 1,000 c.c. per hour. If too rapid
it does not become sufficiently preheated in the glass spiral, and if too
slow there is a more rapid decomposition of the nitro-cellulose by the
oxides of nitrogen which are not removed.

~Decomposition Tube.~--This is of the form and dimensions given by Dr Will
(15 mm. wide and 10 cm. high), the preheating worm being of the thinnest
hydrometer stem tubing. The ground-in exit tube is kept in position by a
small screw clamp with trunnion bearings.

~Bath.~--To permit of two experiments being carried on simultaneously, the
bath is adapted for two decomposition tubes, and is on the principle of
Lothar Meyer's air bath, that is, the bath proper filled with a high-
flashing hydrocarbon oil, and fitted with a lid perforated with two
circular holes for the spiral tubes, is surrounded by an asbestos-covered
envelope, in the interior of which circulate the products of combustion of
numerous small gas jets. The stirrer, agitated by a water motor, or,
better still, a hot-air engine, has a series of helical blades curved to
give a thorough mixing to the oil. Great uniformity and constancy of
temperature are thus obtained. The bath is fitted also with a temperature
regulator and thermometer.

~Reduction Tube~--This is of copper, and consists of two parts, the outer
tube and an inner reaching to nearly the bottom of the former. Into the
inner tube fits a spiral of reduced copper gauze, and into the annular
space between the tubes is fitted a tightly packed reduced copper spiral.
At the bottom the inlet tube dips into a layer of copper oxide asbestos,
on the top of which is a layer of reduced copper asbestos. Through the
indiarubber cork passes a glass tube, which leads the CO_{2} and nitrogen
out of the reduction tube. As the portion of the tube containing the
spirals is heated to redness, water jackets are provided on both inner and
outer tubes to protect the indiarubber cork.

~Nitrogen Measuring Apparatus.~--The measuring tube with zigzag
arrangement is used, having been found very economical in potash. It is
most convenient to take readings by counterbalancing the column of potash
solution and reading off the volume of gas at atmospheric pressure. For
this purpose the tap immediately in front of the measuring tube is
momentarily closed, this having been proved to be without ill effect on
the progress of the test. In all experiments done by this test the air
correction is subtracted from each reading, and the remainder brought to
milligrams of nitrogen with the usual corrections. As objection has
frequently been taken to the test on the ground of difficulty in
interpreting the results obtained, Dr Robertson made a series of
experiments for the purpose of standardising the test, and at the same
time of arriving at the condition under which it could be applied in the
most sensitive and efficient manner. A variety of nitro-celluloses having
been tested, there were chosen as typical, of stable and unstable
products, service gun-cotton on the one hand, and an experimental gun-
cotton, Z, on the other. The first point brought out by these experiments
was the striking uniformity of service gun-cotton, first in regard to the
rectilinear nature of the curve of evolution of nitrogen, and secondly in
regard to the small range within which a large number of results is
included, 15 samples lying between 6.6 and 8.7 mgms. of nitrogen evolved
in four hours. In the case of service gun-cotton, little difference in the
rate of evolution of nitrogen evolved is obtained on altering the rate of
passage of CO_{2} gas through the wide range of 500 c.c. per hour to 2,500
c.c. per hour. With Z gun-cotton (see Fig. 52), however, the case is very
different. Operating at a rate of 1,000 c.c. of CO_{2} per hour, a curve
of nitrogen evolution is obtained, which is bent and forms a good
representation of the inherent instability of the material as proved to
exist from other considerations. Operating at the rate of 1,500 c.c. per
hour, as recommended by Dr Will, the evolution of nitrogen is represented
by a straight line, steeper, however, than that of service gun-cotton. The
rate of passage of CO_{2} was therefore chosen at 1,000 c.c. per hour, or
two-thirds of the rate of Dr Will, and this rate, besides possessing the
advantage claimed of rendering diagnostic the manner of nitrogen evolution
in Z gun-cotton, has in other cases been useful in bringing out
relationships, which the higher rate would have entirely masked.

[Illustration: Fig. 52.--Dr. Robertson's results.]

[Illustration: Fig. 53.--Service Guncotton for Cordite made at a Private
Factory.]

Readings are taken thirty minutes from the time the nitro-cellulose is
heated, and are taken at intervals of fifteen minutes for about four
hours; fresh caustic potash is added every thirty minutes or so. It is
convenient to plot the results in curves. The curves given in Fig. 53 are
from gun-cotton manufacturers in England at a private factory. The rate of
evolution of nitrogen is as follows:--

In 1 hour. In 2 hours. In 3 hours. In 4 hours.
N. N. N. N. in milligrammes.
1.25 2.55 4.5 5.75
1.5 3.25 5.25 6.75
These results are very satisfactory, the gun-cotton was of a very good
quality. Several hours are necessary to remove all the air from the
apparatus. Dr Will stated fifteen minutes in his original paper, but this
has not been found sufficient. It has not been satisfactorily proved that
Will's test can be applied to gelatinised nitro-cellulose powders. It is
convenient to plot the results in curves; the nitrogen is generally given
in cubic centimetres or in milligrammes, and readings taken every fifteen
minutes. The steepness of the curve is a measure of the stability of the
nitro-cellulose which is being examined. The steeper the curve the more
nitrogen is evolved per unit of time, and the less stable the nitro-
cellulose. In the case of unstable nitro-celluloses heated under the
conditions described, the separation of nitrogen is much greater at first
than at a later period. If the nitro-cellulose be very unstable,
explosions are produced. If the separation of nitrogen is uniform during
the prolonged heating, then the nitro-cellulose may be regarded as
"normal." If it be desired to determine the absolute amount of nitrogen
separated from a nitro-cellulose, the following conditions must be
observed:--(1.) Accurate weighing of the nitro-cellulose; (2.)
Determination of the amount of air in the CO_{2}, and deduction of this
from the volume of gas obtained; (3.) Reduction of the volume of the gas
to the volume at 0 deg. C. and 760 mm. pressure.[A]

[Footnote A: See also _Jour. Soc. Chem. Ind._, Dec. 1902, pages 1545-1555,
on the "Stability of Nitro-cellulose" and "Examination of Nitro-
cellulose," Dr Will.]

~Bergrnann and Junk~[A] describe a test for nitro-cellulose that has been
in use in the Prussian testing station for some years. The apparatus
consists of a closed copper bath provided with a condenser and 10
countersunk tubes of 20 cm. length. By boiling amyl-alcohol in the bath,
the tubes can be kept at a constant temperature of 132 deg. C. The explosive
to be tested is placed in a glass tube 35 cm. long and 2 cm. wide, having
a ground neck into which an absorption bulb is fitted. The whole apparatus
is surrounded by a shield, in case of explosion. In carrying out the test,
2 grms. of the explosive are placed in the glass tube and well pressed
down. The absorption bulb is half filled with water, and fitted into the
ground neck of the glass tube, which is then placed in one of the tubes in
the bath previously brought to the boiling point (132 deg. C.). The evolved
oxides of nitrogen are absorbed in the water in the bulb, and at the end
of two hours the tubes are removed from the bath, and on cooling, the
water from the bulb flows back and wets the explosive. The contents of the
tube are filtered and washed, the filtrate is oxidised with permanganate,
and the nitrogen determined as nitric oxide by the Schultze-Tieman method.
The authors conclude that a stable gun-cotton does not evolve more than
2.5 c.c. of nitric oxide per grm. on being heated to 132 deg. C. for two
hours, and a stable collodion-cotton not more than 2 c.c. under the same
conditions. The percentage of moisture in the sample to be tested should
be kept as low as possible. A sample of nitro-cellulose containing 1.97%
of moisture gave an evolution of 2.6 c.c. per grm., while the same sample
with 3.4% moisture gave an evolution of over 50 c.c. per grm. Sodium
carbonate added to an unstable nitro-cellulose diminishes the rate of
decomposition, but if sodium carbonate be intimately mixed with a stable
nitro-cellulose the rate of decomposition will be increased. Calcium
carbonate and mercury chloride have no influence. If an unstable nitro-
cellulose be extracted with alcohol a stable compound is produced. The
percentage solubility of a nitro-cellulose in ether-alcohol rises on
heating to 132 deg. C. A sample which before heating had a solubility of 4.7%
had its solubility increased to 82.5% after six hours' heating.

[Footnote A: _Jour. Soc. Chem. Ind._, xxiii., Oct. 15, 1904, p. 953.]

Mr A.P. Sy (_Jour. Amer. Chem. Soc._, 1903) describes a new stability test
for nitro-cellulose which he terms "The Elastic Limit of Powder Resistance
to Heat." The test consists in heating the powder on a watch glass in an
oven to a temperature of 115 deg. C., after eight hours the watch glass and
powder are weighed and the process repeated daily for six days or less. He
claims that the powder is tested in its natural state, all the products of
decomposition are taken into account, whilst in the old tests only the
acid products are shown, and in the Will test only nitrogen, that it
affords an indication of the effect of small quantities of added
substances or foreign matters on the stability and that it is simple, and
not subject to the variations of the old tests.

Obermueller (_Jour. Soc. Chem. Ind._, April 15, 1905) considers Bergmann
and Junk's test is too complicated and occupies too much time; he proposes
to heat gun-cotton to 140 deg. C. _in vacuo_, and to measure continuously by
means of a mercury manometer the pressure exerted by the evolved gases,
the latter being maintained at constant volume; the rate at which the
pressure increases is a measure of the rate of decomposition of the nitro-
cellulose.

SPECIFIC GRAVITIES OF EXPLOSIVES, &C.

Nitro-glycerine 1.6
Gun-cotton (dry) 1.06
" (25 per cent. water) 1.32
Dynamite No. 1 1.62
Blasting gelatine 1.54
Gelatine dynamite 1.55
Ballistite 1.6
Forcite 1.51
Tonite 1.28
Roburite 1.40
Bellite 1.2-1.4
Carbo-dynamite 1.5
Turpin's cast picric acid 1.6
Nitro-mannite 1.6
Nitro-starch 1.5
Emmensite 1.8
Mono-nitro-benzene 1.2
Meta-di-nitro-benzene 1.575 at 18 deg. C.
Ortho-di-nitro-benzene 1.590 "
Para-di-nitro-benzene 1.625 "
British gunpowder, E.X.E. 1.80
" " S.B.C. 1.85
Cannonite (powder) 1.60
Celluloid 1.35
Cellulose 1.45
Ammonium nitrate 1.707
Mercury fulminate 4.42

TABLE OF THE TEMPERATURE OF DETONATION.

Blasting gelatine 3220 deg.
Nitro-glycerine 3170 deg.
Dynamite 2940 deg.
Gun-cotton 2650 deg.
Tonite 2648 deg.
Picric acid 2620 deg.
Roburite 2100 deg.
Ammonia nitrate 1130 deg.

RELATIVE SENSITIVENESS TO DETONATION (by Professor C.E. Munroe, U.S. Naval
Torpedo Station).

__________________________________________________________________________
|
| Maximum |
| Distance |
| at which |
| Detonation |
| occurred. |
| CM. |
| |
Gun-cotton | 10 | Nitro-glycerine 86.5 nitro-cotton
| | 9.5, camphor 4 per cent.
Explosive gelatine | 20 | NH_{4}NO_{3} 5 parts,
(camphorated) | | C_{6}H_{4}(N0_{3})_{2} 1 part.
Judson powder, R.R.P. | 25 |
Emmensite (No. 259) | 30 |
Rack-a-rock | 32 | KClO_{3} 79 parts,
| | C_{6}H_{5}(NO)_{2} 21 parts.
Bellite | 50 |
Forcite No. 1 | 61 |
Kieselguhr dynamite No. 1 | 64 | 75 per cent. nitro-gycerine.
Atlas powder No. 1 | 74 |
__________________________|____________|_________________________

CHAPTER IX.

_DETERMINATION OF THE RELATIVE STRENGTH OF EXPLOSIVES._

Effectiveness of an Explosive--High and Low Explosives--Theoretical
Efficiency--MM. Roux and Sarrau's Results--Abel and Noble's--Nobel's
Ballistic Test--The Mortar, Pressure, or Crusher Gauge--Lead Cylinders--
The Foot-Pounds Machine--Noble's Pressure Gauge--Lieutenant Walke's
Results--Calculation of Pressure Developed by Dynamite and Gun-Cotton--
Macnab's and Ristori's Results of Heat Developed by the Explosion of
Various Explosives--Composition of some of the Explosives in Common Use
for Blasting, &c.

~The Determination of the Relative Strength of Explosives.~--Explosives
may be roughly divided into two divisions, viz., those which when exploded
produce a shattering force, and those which produce a propulsive force.
Explosives of the first class are generally known as the high explosives,
and consist for the most part of nitro compounds, or mixtures of nitro
compounds with other substances. Any explosive whose detonation is very
rapid is a high explosive, but the term has chiefly been applied to the
nitro-explosives.

The effectiveness of an explosive depends upon the volume and temperature
of the gases formed, and upon the rapidity of the explosion. In the high
explosives the chemical transformation is very rapid, hence they exert a
crushing of shattering effect. Gunpowder, on the other hand, is a low
explosive, and produces a propelling or heaving effect.

The maximum work that an explosive is capable of producing is
proportionate to the amount of heat disengaged during its chemical
transformation. This may be expressed in kilogrammetres by the formula
425Q, where Q is the number of units of heat evolved. The theoretical
efficiency of an explosive cannot, however, be expected in practice for
many reasons.

In the case of blasting rock, for instance:[A]--1. Incomplete combustion
of the explosive. 2. Compression and chemical changes induced in the
surrounding material operated on. 3. Energy expended in the cracking and
heating of the material which is not displaced. 4. The escape of gas
through the blast-hole, and the fissures caused by the explosion. The
proportion of useful work has been estimated to be from 14 to 33 per cent.
of the theoretical maximum potential.

[Footnote A: C.N. Hake, Government Inspector of Explosives, Victoria,
_Jour. Soc. Chem. Ind._, 1889.]

For the purposes of comparison, manufacturers generally rely more upon the
practical than the theoretical efficiency of an explosive. These, however,
stand in the same relation to one another, as the following table of
Messrs Roux and Sarrau will show:--

MECHANICAL EQUIVALENT OF EXPLOSIVES.

Theoretical Work Relative
in Kilos. Value.

Blasting powder (62 per cent. KNO_{3}) 242,335 1.0
Dynamite (75 per cent. nitro-glycerine) 548,250 2.26
Blasting gelatine (92 per cent. nitro-glycerine) 766,813 3.16
Nitro-glycerine 794,563 3.28

Experiments made in lead cylinders give--
Dynamite 1.0
Blasting gelatine 1.4
Nitro-glycerine 1.4

Sir Frederick Abel and Captain W.H. Noble, R.A., have shown that the
maximum pressure exerted by gunpowder is equal to 486 foot-tons per lb. of
powder, or that when 1 kilo, of the powder gases occupy the volume of 1
litre, the pressure is equal to 6,400 atmospheres; and Berthelot has
calculated that every gramme of nitro-glycerine exploded gives 1,320 units
of heat. MM. Roux and Sarrau, of the Depot Centrales des Poudres, Paris,
by means of calorimetric determinations, have shown that the following
units of heat are produced by the detonation of--

Nitro-glycerine 1,784 heat units.
Gun-cotton 1,123 "
Potassic picrate 840 "

which, multiplied by the mechanical equivalent per unit, gives--

Nitro-glycerine 778 metre tons per kilogramme.
Gun-cotton 489 " "
Picrate of potash 366 " "

~Nobel's Ballistic Test.~--Alfred Nobel was the first to make use of the
mortar test to measure the (ballistic) power of explosives. The use of the
mortar for measuring the relative power of explosives does not give very
accurate results, but at the same time the information obtained is of
considerable value from a practical point of view. The mortar consists of
a solid cylinder of cast iron, one end of which has been bored to a depth
of 9 inches, the diameter of the bore being 4 inches. At the bottom of the
bore-hole is a steel disc 3 inches thick, in which another hole has been
bored 3 inches by 2 inches. The mortar (Fig. 54) itself is fitted with
trunnions, and firmly fixed in a very solid wooden carriage, which is
securely bolted down to the ground. The shot used should weigh 28 lbs.,
and be turned accurately to fit the bore of the mortar. Down its centre is
a hole through which the fuse is put.

The following is the method of making an experiment:--A piece of hard wood
is turned in the lathe to exactly fit the hole in the steel disc at the
bottom of the bore. This wooden cylinder itself contains a small cavity
into which the explosive is put. Ten grms. is a very convenient quantity.
Before placing in the mortar, a hole may be made in the explosive by means
of a piece of glass rod of such a size that the detonator to be used will
just fit into it. After placing the wooden cylinder containing the
explosive in the cavity at the bottom of the bore, the shot, slightly
oiled, is allowed to fall gently down on to it. A piece of fuse about a
foot long, and fitted with a detonator, is now pushed through the hole in
the centre of the shot until the detonator is embedded in the explosive.
The fuse is now lighted, and the distance to which the shot is thrown is
carefully measured. The range should be marked out with pegs into yards
and fractions of yards, especially at the end opposite to the mortar. The
mortar should be inclined at an angle of 45 deg.. In experimenting with this
apparatus, the force and direction of the wind will be found to have
considerable influence.

[Illustration: FIG. 54.--MORTAR FOR MEASURING THE BALLISTIC POWER OF
EXPLOSIVES. _A_, Shot; _B_, Steel Disc; _C_, Section of Mortar (Cast
Iron); _D_, Wooden Plug holding Explosive (_E_); _F_, Fuse.]

Mr T. Johnson made some ballistic tests. He used a steel mortar and a shot
weighing 29 Ibs., and he adopted the plan of measuring the distance to
which a given charge, 5 grms., would throw the shot. He obtained the
following results:--

Range in Feet.

Blasting gelatine (90 per cent. nitro-glycerine and nitro-cellulose) 392
Ammonite (60 per cent. Am(NO_{3}) and 10 per cent. nitro-naphthalene) 310
Gelignite (60 per cent. nitro-gelatine and gun-cotton) 306
Roburite (AmNO_{3} and chloro-nitro-benzol) 294
No. 1 dynamite (75 per cent. nitro-gelatine) 264
Stonite (68 per cent. nitro-gelatine and 32 per cent. wood-meal) 253
Gun-cotton 234
Tonite (gun-cotton and nitrates) 223
Carbonite (25 per cent. nitro-gelatine, 40 per cent. wood-meal,
and 30 per cent. nitrates) 198
Securite (KNO_{3} and nitro-benzol) 183
Gunpowder 143

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