_FIRING POINT OF EXPLOSIVES, HEAT TESTS, &c._
Horsley's Apparatus--Table of Firing points--The Government Heat-Test
Apparatus for Dynamites--Nitro-Glycerine, Nitro-Cotton, and Smokeless
Powders--Liquefaction and Exudation Tests--Page's Regulator for Heat-Test
Apparatus--Specific Gravities of Explosives--Table of Temperature of
Detonation, Sensitiveness, &c.
~The Firing Point of Explosives.~--The firing point of an explosive may be
determined as follows:--A copper dish, about 3 inches deep, and 6 or more
wide, and fitted with a lid, also of copper, is required. The lid contains
several small holes, into each of which is soldered a thick copper tube
about 5 mm. in diameter, and 3 inches long, with a rather larger one in
the centre in which to place a thermometer. The dish is filled with Rose's
metal, or paraffin, according to the probable temperature required. The
firing point is then taken thus:--After putting a little piece of asbestos
felt at the bottom of the centre tube, the thermometer is inserted, and a
small quantity of the explosive to be tested is placed in the other holes;
the lid is then placed on the dish containing the melted paraffin or
metal, in such a way that the copper tubes dip below the surface of the
liquid; the temperature of the bath is now raised until the explosive
fires, and the temperature noted. The initial temperature should also be
noted.
THE FIRING POINT OF VARIOUS EXPLOSIVES (by C. E. Munroe).
(Horsley's Apparatus used.)
_____________________________________________________________________
|
| °C.
Nitro-glycerine, 5 years old (a single drop taken) | 203-205
Gun-cotton (compressed military cotton, sp. gr. 1.5) | 192-201
Air-dried gun-cotton, stored for 4 years | 179-187
Ditto, stored for 1 year | 187-189
Air-dried collodion-cotton, long staple "Red Island |
cotton," 3 years old | 186-191
Air-dried collodion, 3 years old, stored wet | 197-199
Hydro-nitro-cellulose | 201-213
Kieselguhr dynamite, No. 1 | 197-200
Explosive gelatine | 203-209
Mercury fulminate | 175-181
Gunpowder (shell) | 278-287
Hill's picric powder (shells) Been in store 10 years. | 273-283
Ditto (musket) Composed of-- | 282-290
Ammonium picrate 42.18 % |
Potassium picrate 53.79 " |
Charcoal (alder) 3.85 " |
________ |
|
99.82 |
Forcite, No. 1 | 187-200
Atlas powder (75% NG) | 175-185
Emmensite, No. 1 Sample had been stored in | 167-184
magazine for some months in |
a wooden box. |
" No. 2 Stored in tin case. | 165-177
" No. 5 " " | 205-217
__________________________________________________________|__________
| |
| °C. |
Powder used in Chassepôt rifle | 191 | By Leygue & Champion.
French gunpowder | 295 | " "
Rifle powder (picrate) | 358 | " "
Cannon | 380 | " "
__________________________________|_________|________________________
Horsley's apparatus consists of an iron stand with a ring support, holding
a hemispherical iron vessel or bath in which solid paraffin is put. Above
this is another movable support, from which a thermometer is suspended,
and so adjusted that its bulb is immersed in the material contained in the
iron vessel. A thin copper cartridge-case, 5/8 inch in diameter and
1-15/16 inch long, is suspended over the bath by means of a triangle, so
that the end of the case is just 1 inch below the surface of the molten
material. On beginning the experiment of determining the firing point of
any explosive, the material in the bath is heated to just above the
melting point; the thermometer is inserted in it, and a minute quantity of
the explosive is placed in the bottom of the cartridge-case. The initial
temperature is noted, and then the cartridge-case containing the explosive
is inserted in the bath. The temperature is quickly raised until the
contents of the cartridge-case flash off or explode, when the temperature
is noted as the _firing point_.
[Illustration: FIG. 46.--HEAT TEST APPARATUS.]
Professor C.E. Munroe, of the U.S. Torpedo Station, has determined the
firing point of several explosives by means of this apparatus.
~The Government Heat Test (Explosives Act, 1875): Apparatus required.~--A
water bath, consisting of a spherical copper vessel _(a)_, Fig. 46, of
about 8 inches diameter, and with an aperture of about 5 inches; the bath
is filled with water to within a quarter of an inch of the edge. It has a
loose cover of sheet copper about 6 inches in diameter _(b)_ and rests on
a tripod stand about 14 inches high _(c)_, which is covered with coarse
wire gauze _(e)_, and is surrounded with a screen of thin sheet copper
_(d)_. Within the latter is placed an argand burner _(f)_ with glass
chimney. The cover _(b)_ has four holes arranged, as seen in Fig. II., No.
4 to contain a Page's[A] or Scheibler's regulator, No. 3 the thermometer,
Nos. 1 and 2 the test tubes containing the explosive to be tested. Around
the holes 1 and 2 on the under side of the cover are soldered three pieces
of brass wire with points slightly converging (Fig. III.); these act as
springs, and allow the test tubes to be easily placed in position and
removed.
[Footnote A: See _Chem. Soc. Jour._, 1876, i. 24. F.J.M. Page.]
~Test Tubes~, from 5-1/4 to 5-1/2 inches long, and of such a diameter that
they will hold from 20 to 22 cubic centimetres of water when filled to a
height of 5 inches; rather thick glass is preferable. Indiarubber
stoppers, fitting the test tubes, and carrying an arrangement for holding
the test papers, viz., a narrow glass tube passing through the centre of
the stopper, and terminating in a platinum wire hook. A glass rod drawn
out and the end turned up to form a hook is better.
~The Thermometer~ should have a range from 30° to 212° F., or from 1° to
100° C. A minute clock is useful.
~Test Paper.~--The test paper is prepared as follows:--45 grains (2.9
grms.) of white maize starch (corn flour), previously washed with cold
water, are added to 8-1/2 oz. of water. The mixture is stirred, heated to
boiling, and kept gently boiling for ten minutes; 15 grains (1 grm.) of
pure potassium iodide (previously recrystallised from alcohol, absolutely
necessary) are dissolved in 8-1/2 oz. of distilled water. The two
solutions are thoroughly mixed and allowed to get cold. Strips or sheets
of white English filter paper, previously washed with water and re-dried,
are dipped into the solution thus prepared, and allowed to remain in it
for not less than ten seconds; they are then allowed to drain and dry in a
place free from laboratory fumes and dust. The upper and lower margins of
the strips or sheets are cut off, and the paper is preserved in well-
stoppered or corked bottles, and in the dark. The dimensions of the pieces
of test paper used are about 4/10 inch by 8/10 inch (10 mm. by 20 mm.).[A]
[Footnote A: When the paper is freshly prepared, and as long as it remains
in good condition, a drop of diluted acetic acid put on the paper with a
glass rod produces no coloration. In process of time it will become
brownish, when treated with the acid, especially if it has been exposed to
sunlight. It is then not fit for use.]
In Germany zinc-iodide starch paper is used, which is considered to be
more sensitive than potassium iodide.
~Standard Tint Paper.~--A solution of caramel in water is made of such
concentration that when diluted one hundred times (10 c.c. made up to 1
litre) the tint of this diluted solution equals the tint produced by the
Nessler test in 100 c.c. water containing .000075 grm. of ammonia, or
.00023505 grm. AmCl. With this caramel solution lines are drawn on strips
of white filter paper (previously well washed with distilled water, to
remove traces of bleaching matter, and dried) by means of a quill pen.
When the marks thus produced are dry, the paper is cut into pieces of the
same size as the test paper previously described, in such a way that each
piece has a brown line across it near the middle of its length, and only
such strips are preserved in which the brown line has a breadth varying
from 1\2 mm. to 1 mm. (1/50 of an inch to 1/25 of an inch).
~Testing Dynamite, Blasting Gelatine, and Gelatine Dynamite.~--Nitro-
glycerine preparations, from which the nitro-glycerine can be extracted in
the manner described below, must satisfy the following test, otherwise
they will not be considered as manufactured with "thoroughly purified
nitro-glycerine," viz., fifteen minutes at 160° F. (72° C.).
~Apparatus required.~--A funnel 2 inches across (_d_), a cylindrical
measure divided into grains (_e_), Fig. 47.
~Mode of Operation.~--About 300 (19.4 grms.) to 400 grains (26 grms.) of
dynamite (_b_), finely divided, are placed in the funnel, which is loosely
plugged by freshly ignited asbestos (_a_). The surface is smoothed by
means of a flat-headed glass rod or stopper, and some clean washed and
dried kieselguhr (_c_) is spread over it to the depth of about 1/8 inch.
Water is then poured on from a wash bottle, and when the first portion has
been soaked up more is added; this is repeated until sufficient nitro-
glycerine has collected in the graduated measure (_e_). If any water
should have passed through, it must be removed from the nitro-glycerine by
filter paper, or the nitro-glycerine may be filtered.
[Illustration: FIG. 47.--APPARATUS FOR SEPARATING THE NlTRO-GLYCERINE FROM
DYNAMITE.]
[Illustration: FIG. 48.--TEST TUBE ARRANGED FOR HEAT TEST.]
~Application of Test.~--The thermometer is fixed so as to be inserted
through the lid of the water bath into the water, which is maintained at
160° F. (72° C.), to a depth of 2-3/4 inches. Fifty grains (= 3.29 grms.)
of nitro-glycerine to be tested are weighed into the test tube, in such a
way as not to soil the sides of the tube (use a pipette). A test paper is
fixed on the hook of the glass rod, so that when inserted into the tube it
will be in a vertical position. A sufficient amount of a mixture of half
distilled water and half glycerine, to moisten the upper half of the
paper, is now applied to the upper edge of the test paper by means of a
glass rod or camel's hair pencil; the cork carrying the rod and paper is
fixed into the test tube, and the position of the paper adjusted so that
its lower edge is about half way down the tube; the latter is then
inserted through one of the holes in the cover to such a depth that the
lower margin of the moistened part of the paper is about 5/8 inch above
the surface cover. The test is complete when the faint brown line, which
after a time makes its appearance at the line of boundary between the dry
and moist part of the paper, equals in tint the brown line of the standard
tint paper.
~Blasting Gelatine, Gelatine Dynamite, Gelignite, &c.~--Fifty grains (=
3.29 grms.) of blasting gelatine are intimately mixed with 100 grains (=
6.5 grms.) of French chalk. This is done by carefully working the two
materials together with a wooden pestle in a wooden mortar. The mixture is
then gradually introduced into the test tube, with the aid of gentle
tapping upon the table between the introduction of successive portions of
the mixture into the tube, so that when the tube contains all the mixture
it shall be filled to the extent of 1-3/4 inch of its height. The test
paper is then inserted as above described for nitro-glycerine. The sample
tested must stand a temperature of 160° F. for a period of ten minutes
before producing a discoloration of the test paper corresponding in tint
to the standard paper.
_N.B._--Non-gelatinised nitro-glycerine preparations, from which the
nitro-glycerine cannot be expelled by water, are tested without any
previous separation of the ingredients, the temperature being as above
160° F., and the time being seven minutes.
~Gun-Cotton, Schultze Gunpowder, E.C. Powder, &c.: A. Compressed Gun-
Cotton.~--Sufficient material to serve for two or more tests is removed
from the centre of the cartridge by gentle scraping, and if necessary,
further reduced by rubbing between the fingers. The fine powder thus
produced is spread out in a thin layer upon a paper tray 6 inches by 4-1/2
inches, which is then placed inside a water oven, kept as nearly as
possible at 120° F. (49° C.). The wire gauze shelves of the oven should be
about 3 inches apart. The sample is allowed to remain at rest for fifteen
minutes in the oven, the door of which is left wide open. After the lapse
of fifteen minutes the tray is removed and exposed to the air of the room
for two hours, the sample being at some point within that time rubbed upon
the tray with the hand, in order to reduce it to a fine and uniform state
of division.
The heat test is performed as before, except that the temperature of the
bath is kept at 170° F. (66° C.), and regulator set to maintain that
temperature. Twenty grains (1.296 grm.) are used, placed in the test tube,
gently pressed down until it occupies a space of as nearly as possible
1-5/10 inch in the test tube of dimensions previously specified. The fine
cotton adhering to the sides of the tube can be removed by a clean cloth
or silk handkerchief. The paper is moistened by touching the upper edge
with a drop of the 50 per cent. glycerine solution, the tube inserted in
the bath to a depth of 2-1/2 inches, measured from the cover, the
regulator and thermometer being inserted to the same depth. The test paper
is to be kept near the top of the test tube, but clear of the cork, until
the tube has been immersed for about five minutes. A ring of moisture will
about this time be deposited upon the sides of the test tube, a little
above the cover of the bath. The glass rod must then be lowered until the
lower margin of the moistened part of the paper is on a level with the
bottom of the ring of moisture in the tube. The paper is now closely
watched, The test is complete when a very faint brown coloration makes its
appearance at the line of boundary between the dry and moist parts of the
paper. It must stand the test for not less than ten minutes at 170° F.
(The time is reckoned from the first insertion of the tube in the bath
until the appearance of a discoloration of the test paper.)
~B. Schultze Powder, E.C. Powder, Collodion-Cotton, &c.~--The sample is
dried in the oven as above for fifteen minutes, and exposed for two hours
to the air. The test as above for compressed gun-cotton is then applied.
~C. Cordite~ must stand a temperature of 180° F. for fifteen minutes. The
sample is prepared as follows:--Pieces half an inch long are cut from one
end of every stick selected for the test: in the case of the thicker
cordites, each piece so cut is further subdivided into about four
portions. These cut pieces are then passed once through the mill, the
first portion of material which passes through being rejected on account
of the possible presence of foreign matter from the mill. The ground
material is put on the top sieve of the nest of sieves, and sifted. That
portion which has passed through the top sieve and been stopped by the
second is taken for the test. If the mill is properly set, the greater
portion of the ground material will be of the proper size. If the volatile
matter in the explosive exceeds 0.5 per cent., the sifted material should
be dried at a temperature not exceeding 140° F, until the proportion does
not exceed 0.5 per cent. After each sample has been ground, the mill must
be taken to pieces and carefully cleaned. The sieves used consist of a
nest of two sieves with holes drilled in sheet copper. The holes in the
top sieve have a diameter = 14 B.W.G., those in the second = 21 B.W.G.
If too hard for the mill, the cordite may be softened by exposure to the
vapour of acetone,[A] or reduced, to the necessary degree of subdivision
by means of a sharp moderately-coarse rasp. Should it have become too soft
in the acetone vapour for the mill, it should be cut up into small pieces,
which may be brought to any desired degree of hardness by simple exposure
to air. Explosives which consist partly of gelatinised collodion-cotton,
and partly of ungelatinised gun-cotton, are best reduced to powder by a
rasp, or softened by exposure to mixed ether and alcohol vapour at a
temperature of 40° F. to 100° F.
[Footnote A: Mr W. Cullen _(Jour. Soc. Chem. Ind._, Jan. 31, 1901) says:--
"Undoubtedly the advent of the horny smokeless powders of modern times has
made it a little difficult to give the test the same scope as it had when
first introduced." As a rule a simple explanation can be found for every
apparently abnormal result, and in the accidental retention of a portion
of the solvent used in the manufacture, will frequently be found an
explanation of the trouble experienced.]
~Ballistite.~--In the case of ballistite the treatment is the same, except
that when it is in a very finely granulated condition it need not be cut
up.
~Guttmann's Heat Test.~--This test was proposed by Mr Oscar Guttmann in a
paper read before the Society of Chemical Industry (vol. xvi., 1897), in
the place of the potassium iodide starch paper used in the Abel test. The
filter paper used is wetted with a solution of diphenylamine[A] in
sulphuric acid. The solution is prepared as follows:--Take 0.100 grm. of
diphenylamine crystals, put them in a wide-necked flask with a ground
stopper, add 50 c.c. of dilute sulphuric acid (10 c.c. of concentrated
sulphuric acid to 40 c.c. of water), and put the flask in a water bath at
between 50° and 55° C. At this temperature the diphenylamine will melt,
and at once dissolve in the sulphuric acid, when the flask should be taken
out, well shaken, and allowed to cool. After cooling, add 50 c.c. of
Price's double distilled glycerine, shake well, and keep the solution in a
dark place. The test has to be applied in the following way:--The
explosives that have to be tested are finely subdivided, gun-cotton,
nitro-glycerine, dynamite, blasting gelatine, &c., in the same way as at
present directed by the Home Office regulations. Smokeless powders are all
to be ground in a bell-shaped coffee mill as finely as possible, and
sifted as hitherto. 1.5 grm. of the explosive (from the second sieve in
the case of smokeless powder) is to be weighed off and put into a test
tube as hitherto used. Strips of well-washed filter paper, 25 mm. wide,
are to be hung on a hooked glass rod as usual. A drop of the diphenylamine
solution is taken up by means of a clean glass rod, and the upper corners
of the filter paper are touched with it, so that when the two drops run
together about a quarter of the filter paper is moist. This is then put
into the test tube, and this again into the water bath, which has been
heated to 70° C. The heat test reaction should not show in a shorter time
than fifteen minutes. It will begin by the moist part of the paper
acquiring a greenish yellow colour, and from this moment the paper should
be carefully watched. After one or two minutes a dark blue mark will
suddenly appear on the dividing line between the wet and dry part of the
filter paper, and this is the point that should be taken.
[Footnote A: Dr G. Spica (_Rivista_, Aug. 1897) proposes to use
hydrochloride of meta-phenylenediamine.]
~Exudation and Liquefaction Test for Blasting Gelatine, Gelatine Dynamite,
&c.~--A cylinder of blasting gelatine, &c., is to be cut from the
cartridge to be tested, the length of the cylinder to be equal to its
diameter, and the ends being cut flat. The cylinder is to be placed on end
on a flat surface without any wrapper, and secured by a pin passing
vertically through its centre. In this condition the cylinder is to be
exposed for 144 consecutive hours (six days and nights) to a temperature
ranging from 85° to 90° F. (inclusive), and during such exposure the
cylinder shall not diminish in height by more than one-fourth of its
original height, and the upper cut surface shall retain its flatness and
the sharpness of its edge.
~Exudation Test.~--There shall be no separation from the general mass of
the blasting gelatine or gelatine dynamite of a substance of less
consistency than the bulk of the remaining portion of the material under
any conditions of storage, transport, or use, or when the material is
subjected three times in succession to alternate freezing and thawing, or
when subjected to the liquefaction test before described.
~Picric Acid.~--The material shall contain not more than 0.3 part of
mineral or non-combustible matter in 100 parts by weight of the material
dried at 160° F. It should not contain more than a minute trace of lead.
One hundred parts of the dry material shall not contain more than 0.3 part
of total (free and combined) sulphuric acid, of which not more than 0.1
part shall be free sulphuric acid. Its melting point should be between
248° and 253° F.
~Ammonite, Bellite, Roburite, and Explosives of similar Composition.~--
These are required to stand the same heat test as compressed
nitro-cellulose, gun-cotton, &c.
~Chlorate Mixtures.~--The material must not be too sensitive, and must
show no tendency to increase in sensitiveness in keeping. It must contain
nothing liable to reduce the chlorate. Chlorides calculated as potassium
chloride must not exceed 0.25 per cent. The material must contain no free
acid, or substance liable to produce free acid. Explosives of this class
containing nitro-compounds will be subject to the heat test.
~Page's Regulator.~--The most convenient gas regulator to use in
connection with the heat-test apparatus is the one invented by Prof.
F.J.M. Page, B.Sc.[A] (Fig. 49). It is not affected by variations of the
barometric pressure, and is simple and easy to fit up. It consists of a
thermometer with an elongated glass bulb 5/8 inch diameter and 3 inches
long. The stem of the thermometer is 5 inches long and 1/8 inch to 3/16
inch internal diameter. One and a half inch from the top of the stem is
fused in at right angles a piece of glass tube, 1 inch long, of the same
diameter as the stem, so as to form a T. A piece of glass tube (A), about
7/16 inch external diameter and 1-1/2 inch long, is fitted at one end with
a short, sound cork (C, Fig. 50). Through the centre of this cork a hole
is bored, so that the stem of the thermometer just fits into it. The other
end of this glass tube is closed by a tightly fitting cork, preferably of
indiarubber (I), which is pierced by a fine bradawl through the centre.
Into the hole thus made is forced a piece of fine glass tube (B) 3 inches
long, and small enough to fit loosely inside the stem of the thermometer.
[Footnote A: _Chemical Soc. Jour._, 1876, i. 24.]
The thermometer is filled by pouring in mercury through a small funnel
until the level of the mercury (when the thermometer is at the desired
temperature) is about 1-1/2 inch below the T. The piece of glass tube A,
closed at its upper extremity by the cork I, through which the fine glass
tube B passes into the stem of the thermometer, is now filled by means of
the perforated cork at its lower extremity on the stem of the thermometer.
The gas supply tube is attached to the top of the tube A, the burner to
the T, so that the gas passes in at the top, down the fine tube B, rises
in the space between B and the inside wall of the stem of the thermometer,
and escapes by the T. The regulator is set for any given temperature by
pushing the cork C, and consequently the tubes A and B, which are firmly
attached to it, up or down the stem of the thermometer, until the
regulator just cuts off the gas at the desired temperature.
[Illustration: FIG. 49.--PAGE'S REGULATOR.]
[Illustration: FIG. 50.--PAGE'S GAS REGULATOR, SHOWING BYE-PASS AND
CUT-OFF ARRANGEMENT.]
As soon as the temperature falls, the mercury contracts, and thus opens
the end of the tube B. The gas is thus turned on, and the temperature
rises until the regulator again cuts off the gas. In order to prevent the
possible extinction of the flame by the regulator, the brass tube which
carries the gas to the regulator is connected with the tube which brings
the gas from the regulator to the burner by a small brass tap (Fig. 2).
This tap forms an adjustable bye-pass, and thus a small flame can be kept
burning, even though the regulator be completely shut off. It is obvious
that the quantity of gas supplied through the bye-pass must always be less
than that required to maintain the desired temperature. This regulator,
placed in a beaker of water on a tripod, will maintain the temperature of
the water during four or five hours within 0.2° C., and an air bath during
six weeks within 0.5° C.
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° 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° 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° 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° 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° 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° 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° 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.
Obermüller (_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° 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° 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°
Nitro-glycerine 3170°
Dynamite 2940°
Gun-cotton 2650°
Tonite 2648°
Picric acid 2620°
Roburite 2100°
Ammonia nitrate 1130°
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 |
__________________________|____________|_________________________