Nitro Explosives: A Practical Treatise by P. Gerald Sanford

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The usual proportion of the constituents is 2 parts pyroxyline and 1 part
camphor. In Trebouillet and De Besancele's process, 100 parts of
pyroxyline are intimately mixed with from 40 to 50 parts camphor, and
moulded together by strong pressure in a hot press, and afterwards dried
by exposure to air, desiccated by calcium chloride or sulphuric acid. The
usual method is, however, to dissolve the camphor in the least possible
quantity of alcohol, and sprinkle the solution over the dry pyroxyline,
which is then covered with a second layer of pyroxyline, and the whole
again treated with the camphor solution, the addition of pyroxyline and
camphor solution being repeated alternately until the requisite amount of
celluloid mixture is obtained.

The mass, which sinks together in transparent lumps, is worked for about
an hour between cold iron rollers, and then for the same period between
rollers which can be gently heated by steam. The layer of celluloid
surrounding the rollers is then cut away and again pressed, the resulting
cake, which is now about 1 cm. thick, being cut into plates of about 70
cm. long and 30 cm. broad. These are placed one above the other, and
strongly pressed together by hydraulic pressure at a temperature of about
70 deg. for twenty-four hours. The thick cakes are once more cut into plates
of the desired thickness, and placed in a chamber heated from 30 deg. to 40 deg.
for eight to fourteen days, whereby they become thoroughly dry, and are
readily made into various articles either by being moulded while warm
under pressure, cut, or turned. Occasionally other liquids, e.g., ether
and wood spirit, are used in place of alcohol as solvents for the camphor.

Celluloid readily colours, and can be marbled for manufacturing purposes,
&c. It is highly inflammable and not explosive even under pressure, and
may be worked under the hammer or between rollers without risk. It softens
in boiling water, and may be moulded or pressed. Its specific gravity
varies slightly with its composition and with the degree of pressure it
has received. It is usually 1.35. It appears to be merely a mixture of its
components, since by treatment with appropriate solvents the camphor may
be readily extracted, and on heating the pyroxyline burns away while the
camphor volatilises.

The manufacture of pyroxyline for the purpose of making celluloid has very
much increased during recent years, and with this increase of production
improved methods of manufacture have been invented. A series of
interesting papers upon the manufacture of pyroxyline has been published
by Mr Walter D. Field, of New York, in the _Journal of the American
Chemical Society_[A] from which the following particulars are taken:--

[Footnote A: Vol. xv., No. 3, 1893; Vol. xvi., No. 7, 1894; Vol. xvi., No.
8, 1894. Figs. 19, 20, 21, 22, and 23 are taken from Mr Field's paper.]

~Selection of the Fibre.~--Cotton fibre, wood fibre, and flax fibre in the
form of raw cotton, scoured cotton, paper, and rags are most generally
used, and give the best results. As the fibres differ greatly in their
structure, they require different methods of nitrating. The cotton fibre
is a flattened hollow ribbon or collapsed cylindrical tube, twisted a
number of times, and closed at one end to form a point. The central canal
is large, and runs nearly to the apex of the fibre. Its side walls are
membraneous, and are readily penetrated by the mixed acids, and
consequently the highest nitration results. In the flax fibre the walls
are comparatively thick, the central canal small; hence it is to be
presumed that the nitration must proceed more slowly than in the case of
cotton. The New Zealand flax gives the most perfectly soluble nitrates of
any of the flaxes. Cotton gives a glutinous collodion, and calico a fluid
collodion. One of the largest manufacturers of pyroxyline in the States
uses the "Memphis Star" brand of cotton. This is an upland cotton, and its
fibres are very soft, moist, and elastic. Its colour is light creamy
white, and is retained after nitration. The staple is short, and the twist
inferior to other grades, the straight ribbon-like filaments being quite
numerous. This cotton is used carded, but not scoured. This brand of
cotton contains a large quantity of half and three-quarter ripe fibre,
which is extremely thin and transparent, distributed throughout the bulk
of the cotton (Monie., Cotton Fibre, 67). Mr Field says, "This is a
significant fact when it is known that from this cotton an extremely
soluble pyroxyline can be produced."

Pyroxyline of an inferior grade as regards colour only can be produced
from the cotton wastes of the trade. They must be scoured before they are
fit for nitrating. Paper made from the pulps of sulphite and sulphate
processes is capable of yielding a very soluble pyroxyline. It can be
nitrated at high temperatures and still yield good results. Tissue paper
made from flax fibre is also used after being cut into squares.

Mowbray (U.S.P., No. 443, 105, 3rd December 1890) says that a pure cotton
tissue paper less than 1/500 inch in thickness, thin as it is, takes on a
glutinous or colloid surface, and thus requires some thirty minutes to
enable the nitration to take place. With a thicker paper only the surface
would be nitrated. He therefore uses a fibre that has been saturated with
a solution of nitrate of soda, and afterwards dried slowly, claiming that
the salt crystallises in the fibre, or enters by the action termed osmose,
and opens up the fibre to the action of the acid. This process would only
be useful when the cotton is to be nitrated at a low temperature. At a
high temperature it would be unnecessary.

Dietz and Wayne (U.S.P., No. 133, 969) use ramie, rheca, or China grass
for producing a soluble pyroxyline. That made from ramie is always of
uniform strength and solubility, and requires a smaller quantity of
solvent to dissolve it than that made from cotton. Mr Field's experience,
however, is entirely contrary to this statement. Such is the influence of
the physical form of the fibre on the process of nitration, that when flax
fibre and cotton fibre are nitrated with acid mixtures of exactly the same
strength, and at the same temperature, the solution of the first is
glutinous or thick, and the second fluid or thin. By simply nitrating at a
higher temperature than the cotton, the flax will yield a pyroxyline
giving an equally fluid collodion.

The presence of chlorine in the fibre must be carefully avoided, as such a
fibre will yield an acid product which cannot be washed neutral. The fibre
must be dry before nitration; and this is best done, according to Mr
Field, by using the form of drier used in drying wool.

~Nitration of the Fibre.~--Mixed cotton and flax fibre in the form of
paper, from 2/1000 to 3/1000 inch thick, and cut into 1-inch squares, is
nitrated by the Celluloid Manufacturing Company, and the same paper, left
in long strips, 1 inch wide, is used for nitration by the Xylonite
Manufacturing Company, of North Adams, Mass. (U.S.A.).

The Celluloid Company introduce the cut paper into the mixed acids by
means of a hollow, rapidly revolving tube, flared at the lower end, and
immersed in the mixed acids. The centrifugal force of the revolving tube
throws the paper towards the sides of the vessel, leaving the centre of
the vessel ready for fresh paper.

The Xylonite Company simply cut the paper into long strips, and introduce
it into the mixed acids by means of forks. The arrangement used by this
Company for holding the mixed acids is a cylindrical vessel divided into a
number of sections, the whole revolving like a turntable, thus allowing
the workman to nitrate successively each lot of paper at a given point.
This Company did not remove the acid from the paper after its immersion,
but plunged it immediately into the water, thus losing a large proportion
of the waste acid. The Celluloid Company, by using the paper in smaller
pieces, and more paper to a pound of acid, and wringing the mixed acid
from the paper before immersion in water, had a better process of
nitration.

Other manufacturers use earthenware vessels, and glass or steel rods,
hooked at one end, having small pieces of rubber hose pulled over the
other end to prevent the hand from slipping. The form of vessel in general
use is that given in Fig. 23. It is large enough to nitrate 1 lb. of
cotton at a time. The hook at one end of the rod enables the workman to
pull the pyroxyline apart, and thus ensures saturation of the fibre. In
the winter the room in which the nitrating is done must be kept at a
temperature of about 70 deg. F. in order to secure equality in the batches.

[Illustration: FIG. 23.--VESSEL FOR NITRATING COTTON OR PAPER.]

The nitrating apparatus of White and Schupphaus (U.S.P., No. 418, 237, 89)
Mr Field considers to be both novel and excellent. The cage (Fig. 24),
with its central perforated cylinder (Fig. 25), is intended to ensure the
rapid and perfect saturation of the tissue paper used for nitrating. The
patentees say that no stirring is required with their apparatus. This,
says Mr Field, might be true when paper is used, or even cotton, when the
temperature of nitration is from 30 deg. to 35 deg. C., but would not be true if
the temperature were raised to 50 deg. to 55 deg. C. The process is as follows:--
The paper is nitrated in the cage (Fig. 25), the bottom of which is formed
by the flanged plate C, fastened to the bottom of the internal cylinder B.
After nitration the cage is carried to a wringer, which forms the basket,
and the acids removed. Finally, the cage is taken to a plunge tank, where
the paper is removed from the cage by simply pulling out the central
perforated cylinder B. Fig. 26 shows the nitrating pot, with its automatic
cover. The plunge tank is shown in plan and section in Figs. 28 and 29.
This apparatus is suitable for the nitration of cotton fibre in bulk at
high or low temperatures. Other methods that have been patented are
Mowbray's (U.S.P., No. 434, 287), in which it is proposed to nitrate paper
in continuous lengths, and Hyatt's (U.S.P., No. 210, 611).

[Illustration: FIG. 24.--CENTRAL PERFORATED CYLINDER.]

[Illustration: FIG. 25.--THE CAGE. WHITE AND SCHUPPHAUS' NITRATING
APPARATUS.]

[Illustration: FIG. 26.--CELLULOID NITRATING POT.]

[Illustration: FIG. 27.--ANOTHER VIEW.]

[Illustration: FIGS. 28, 29.--PLUNGE TANK, IN PLAN AND SECTION.]

~The Acid Mixture.~--Various formulae have been published for producing
soluble nitro-cellulose. In many instances, although the observations were
correct for the single experiment, a dozen experiments would have produced
a dozen different products. The composition of the acids used depends upon
the substance to be nitrated, and the temperature at which the nitration
will be worked. Practically there are three formulae in general use--the
one used by the celluloid manufacturers; another in which the cotton is
nitrated at high temperatures; and a third in which the temperature of the
immersion is low, and the time of nitration about six hours. Of the three,
the best method is the last one, or the one in which the cotton is
immersed at a low temperature, and then the reaction allowed to proceed in
pots holding from 5 to 10 lbs. of cotton. The formula used by the
celluloid manufacturers for the production of the low form of nitrated
product which they use is:--

Sulphuric acid 66 parts by weight.
Nitric acid 17 " "
Water 17 " "

Temperature of immersion, 30 deg. C. Time, twenty to thirty minutes.

The cellulose is used in the form of tissue paper 2/1000 inch thick, 1 lb.
to 100 of acid mixture. The nitro-cellulose produced by this formula is
very insoluble in the compound ethers and other solvents of pyroxyline,
and is seemingly only converted or gelatinised by the action of the
solvent. The next formula produces a mixture of tetra-and penta-nitro-
celluloses hardly soluble in methyl-alcohol (free from acetone), but very
soluble in anhydrous compound ethers, ketones, and aldehydes:--

Nitric acid, sp. gr. 1.435 8 lbs.
Sulphuric acid, sp. gr. 1.83 15-3/4 lbs.
Cotton 14 oz.

Temperature of nitration, 60 deg. C. Time of immersion, forty-five minutes.

The 60 deg. of temperature is developed by mixing the acids together. The
cotton is allowed to remain in the acid until it feels "short" to the rod.

The following table, due to Mr W.D. Field, shows very plainly the great
variation in the time of the immersion and the temperature by seemingly
very slight causes. It extends over fourteen working days, during which
time it rained four days. The formula used is that given above, except
that the specific gravity of the nitric acid is somewhat lower. The
product obtained differs only from that produced by using nitric acid of
specific gravity 1.43 in being soluble in methyl-alcohol. From 30 to 35
lbs. of pyroxyline were produced in each of the fourteen days.

A careful examination of this table will prove very instructive. The
increase in yield varies from 31 per cent. to nothing, and the loss runs
as high as 10 per cent., yet care was taken to make the product uniform in
quality. On the days it rained there was a loss, with the exception of the
fourth day, when there was neither a loss nor a gain. On the days it was
partly clear, as just before or after rain, the table shows a loss in
product. We can explain this fact by reason of the moisture-absorbing
qualities of the cotton. On the rainy days it would absorb the moisture
from the air until, when immersed in the acids, they were weakened, and
the fibre dissolved more or less in weakened acid, producing what is known
as "burning" in the batch. It will also be noticed that on days which show
a loss, the time of the immersion was correspondingly short, as on the
a loss, the time of the immersion was correspondingly short, as on the
tenth, twelfth, and seventh days.

______________________________________________________________________
| | | |
| | Specific Gravity. | Time. |
| |_____________________|_______________________________|
| | | | | | | |
| |H_{2}S0_{4}.|HNO_{3}.|Hours.|Minutes.|Hours.|Minutes.|
|________________|____________|________|______|________|______|________|
| | | | | | | |
| 1. Clear | 1.838 | 1.4249 | ... | 20 | 4 | ... |
| 2. " | 1.837 | 1.4249 | ... | 20 | 2 | ... |
| 3. Cloudy | 1.837 | 1.4226 | ... | 45 | 2 | ... |
| 4. Rain | 1.837 | 1.420 | ... | 20 | 1 | 20 |
| 5. Clear | 1.8377 | 1.42 | 1 | 15 | 2 | ... |
| 6. Rainy | 1.8391 | 1.422 | ... | 35 | 1 | 40 |
| 7. Cloudy | 1.835 | 1.4226 | ... | 20 | ... | 35 |
| 8. Clear | 1.835 | 1.422 | ... | 35 | 1 | 10 |
| 9. Partly Clear| 1.824 | 1.4271 | ... | 20 | 1 | ... |
|10. " | 1.83 | 1.4271 | ... | 10 | ... | 25 |
|11. Cloudy | 1.832 | 1.425 | ... | 10 | ... | 50 |
|12. Rainy | 1.822 | 1.425 | ... | 10 | ... | 20 |
|13. Partly CLear| 1.8378 | 1.4257 | ... | 60 | 1 | 40 |
|14. Cloudy | 1.837 | 1.4257 | 1 | 56 | 4 | 40 |
|________________|____________|________|______|________|______|________|
| | | |
| |Temp., Deg. C. | Percentage |
| |_______________|___________________|
| | | | | |
| | From | To | Increase. | Loss. |
|________________|_______|_______|___________|_______|
| | | | | |
| 1. Clear | 57 deg. | 62 deg. | 31 | ... |
| 2. " | 60 deg. | 62 deg. | 18 | ... |
| 3. Cloudy | 60 deg. | 62 deg. | 7 | ... |
| 4. Rain | 60 deg. | 63 deg. | 0 | 0 |
| 5. Clear | 58 deg. | 62 deg. | 15 | ... |
| 6. Rainy | 58 deg. | 62 deg. | ... | 2 |
| 7. Cloudy | 62 deg. | 65 deg. | ... | 10 |
| 8. Clear | 60 deg. | 62 deg. | 5 | ... |
| 9. Partly Clear| 50 deg. | 60 deg. | ... | 3 |
|10. " | 58 deg. | 60 deg. | ... | 10 |
|11. Cloudy | 58 deg. | 60 deg. | 8 | ... |
|12. Rainy | 58 deg. | 60 deg. | ... | 10 |
|13. Partly CLear| 50 deg. | 58 deg. | 20 | ... |
|14. Cloudy | 50 deg. | 60 deg. | 16 | ... |
|________________|_______|_______|___________|_______|

The lesson this table teaches is, that it is almost impossible to nitrate
cellulose in small quantities, and get uniform results, when the nitration
is carried on at high temperatures. As regards the solubility of
pyroxyline, Parks found that nitro-benzene, aniline, glacial acetic acid,
and camphor, dissolved in the more volatile solvents methyl-alcohol and
alcohol-ether, were much the best solvents for producing a plastic, as
they are less volatile, and develop greater solvent action under the
influence of heat. Nitro-benzene gives a solution that is granular; it
seems to merely convert the pyroxyline, and not to dissolve it; but on the
addition of alcohol, a solution is at once obtained, and the granular
appearance disappears, and the solution becomes homogeneous. The acid
mixture and the method of nitrating have much to do with the action of the
various solvents, so also has the presence of water.

Dr Schupphaus found that propyl and isobutyl alcohols with camphor were
active solvents, and the ketones, palmitone, and stearone in alcohol
solution, also alpha- and beta-naphthol, with alcohol and anthraquinone
(diphenylene diketone) in alcoholic solution, and also iso-valeric
aldehyde and its derivatives, amyliden-dimethyl and amyliden-diethyl
ethers.

August Sayer (U.S.P., No. 470,451) finds diethyl-ketone, dibutyl-ketone,
di-pentyl-ketone, and the mixed ketones,[A] methyl-ethyl, methyl-propyl,
methyl-butyl, methyl-amyl, and ethyl-butyl ketones are active solvents of
pyroxyline; and Paget finds that although methyl-amyl oxide is a solvent,
that ethyl-amyl oxide is not.

[Footnote A: Ketones are derived from the fatty acids by the substitution
of the hydroxyl of the latter by a monad positive radical. They thus
resemble aldehydes in constitution. The best-known ketone is acetone
CH_{3}CO.CH_{3}. Mixed ketones are obtained by distilling together salts
of two different fatty acids. Thus potassic butyrate and potassic acetate
form propyl-methyl-ketone--

C(C_{2}H_{5})H_{2}
|
CO.CH_{3}]

The solvents of pyroxyline can be divided into general classes--First,
those which are solvents without the aid of heat or solution in alcohol;
second, those that are solvents when dissolved in alcohol. These solvents
are those which also develop a solvent action when heated to their melting
point in combination with pyroxyline.

Mr W.D. Field groups the solvents of pyroxyline into classes thus: Two of
the monohydric alcohols; compound ethers of the fatty acids with
monohydric alcohols, aldehydes; simple and mixed ketones of the fatty acid
series. These four classes include the greater number of the solvents of
pyroxyline. Those not included are as follows:--Amyl-nitrate and nitrite,
methylene-di-methyl ether, ethidene-diethyl ether, amyl-chloracetate,
nitro-benzene and di-nitro-benzene, coumarin, camphor, glacial acetic
acid, and mono-, di-, and tri-acetin.

Richard Hale uses the following solvent:--Amyl-acetate, 4 volumes;
petroleum naphtha, 4 volumes; methyl-alcohol, 2 volumes; pyroxyline, 4 to
5 ounces to the gallon of solvent. Hale used petroleum naphtha to hasten
the drying qualities of the varnish, so that it would set on the article
to be varnished before it had a chance to run off. It is, however, the
non-hygroscopic character of the solvent that makes the varnish
successful. This formula is very largely used for the production of
pyroxyline varnish, which is used for varnishing pens, pencils, &c., also
brass-work and silver-ware.

The body known as oxy-cellulose[A] is formed by the action of nitric acid
upon cellulose when boiled with it. The quantity formed is about 30 per
cent. of cellulose acted upon. When washed free from acid, it gelatinises.
It is then soluble in dilute alkalies, and can be reprecipitated from
solution by alcohol, acids, or saline solutions. Messrs Cross and Bevan
assign to it the formula C_{18}H_{26}O_{16}. It dissolves in concentrated
sulphuric acid, and with nitric acid forms a nitro body of the formula
C_{18}H_{23}O_{16}3(NO_{2}), which is prepared as follows:--The gelatinous
oxy-cellulose is washed with strong nitric acid until free from water, and
is then diffused through a mixture of equal volumes of strong sulphuric
and nitric acids, in which it quickly dissolves. The solution, after
standing for about an hour, is poured in a fine stream into a large volume
of water, by which the "nitro" body is precipitated as a white flocculent
mass. The product, after drying at 110 deg. C., was found upon analysis to
contain 6.48 per cent. nitrogen.

[Footnote A: "On the Oxidation of Cellulose," by C.F. Cross and E.J.
Bevan, _Jour. Chem. Soc._, 1883, p. 22.]

MISCELLANEOUS NITRO-EXPLOSIVES.

~Nitro-Starch.~--It is only recently that, by means of the process
introduced by the "Actiengesellschaft Dynamit Nobel," it has been possible
to make this explosive upon the manufacturing scale. Nitro-starch has been
known since 1883, when Braconnot discovered it, and called it xyloidine.
Its formula is C_{6}H_{8}O_{3}(NO_{3})_{2}, but Dr Otto Muehlhaeusen has
lately succeeded in preparing higher nitrated compounds, viz.:--

(_a._) C_{6}H_{7-1/2}O_{2-1/2}(NO_{3})_{2-1/2}.

(_b._) C_{6}H_{7}O_{4}(NO_{3})_{3}.

Or doubling the molecule of starch:--

Nitrogen.
i. Tetra-nitro-starch C_{12}H_{16}O_{6}(ONO_{2})_{4} 11.11 per cent.
ii. Penta-nitro-starch C_{12}H_{15}O_{5}(ONO_{2})_{5} 12.75 "
iii. Hexa-nitro-starch C_{12}H_{14}O_{4}(ONO_{2})_{6} 14.14 "

He regards them as true ethers (esters) of nitric acid. Thus on treatment
with sulphuric acid, these compounds yield NO_{3}H, the residue O.NO_{2}
thus appearing to be replaced by the sulphuric acid residue. On treatment
with a solution of ferrous chloride, nitric oxide and "soluble" starch are
regenerated. On shaking with sulphuric acid over mercury, all the nitrogen
is split off as NO.

Tetra-nitro-starch is prepared upon the large scale as follows:--A
quantity of potato-starch is taken and exposed in some suitable
desiccating apparatus at a temperature of 100 deg. C. until all the moisture
which it contains is completely driven off. It is then reduced to a fine
powder by grinding, and dissolved in nitric acid of specific gravity
1.501. The vessel in which this solution is accomplished is made of lead,
and must be provided with two jackets, cooled by means of water. It should
further be fitted with a screw-agitator, in order to keep the nitric acid
circulating freely. The charge of starch is introduced through an opening
in the cover of this digesting vessel, and the proportions of acid to
starch are 10 kilogrammes of starch to 100 kilos. of acid. The temperature
is kept within the limits 20 deg. to 25 deg. C. When the solution of the starch is
complete, the liquid is conducted into a precipitating apparatus, which is
also provided with a cooling jacket, for the purpose of regulating the
temperature. The bottom of this vessel is double and perforated, and here
is placed a layer of gun-cotton to act as a filter. This vessel is filled
with spent nitro-sulphuric acid obtained as a waste product from the
nitro-glycerine manufactory, and the solution of starch in nitric acid is
sprayed into it through an injector worked by compressed air, whereby the
nitro-starch is thrown down in the form of a fine-grained powdery
precipitate.

In order to precipitate 100 kilos. of the acid solution of starch, it is
necessary to employ 500 kilos. of spent nitro-sulphuric acid. As it is
precipitated the nitro-starch collects on the gun-cotton filter, and the
acid liquor is run off through a tap placed beneath the perforated double
bottom of the vessel, and of course below the filter pad. The precipitated
starch is further cleansed from acid by repeated washings and by pressure,
until all trace of acidity has been eliminated, and the substance exhibits
a neutral reaction. The next step is to treat the nitro-starch with a 5
per cent. solution of soda, in contact with which it is allowed to stand
for at least twenty-four hours. The product is then ground up until a sort
of "milk" or emulsion is obtained, and lastly treated with a solution of
aniline, so that when pressed into cake, it contains about 33 per cent. of
water, and 1 per cent. of aniline.

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