_NITRO-CELLULOSE, &c._
Cellulose Properties--Discovery of Gun-Cotton--Properties of Gun-Cotton--
Varieties of Soluble and Insoluble Gun-Cottons--Manufacture of Gun-Cotton--
Dipping and Steeping--Whirling out the Acid--Washing--Boiling--Pulping--
Compressing--The Waltham Abbey Process--Le Bouchet Process--Granulation of
Gun-Cotton--Collodion-Cotton--Manufacture--Acid Mixture used--Cotton used,
&c.--Nitrated Gun-Cotton--Tonite--Dangers in Manufacture of Gun-Cotton--
Trench's Fire-Extinguishing Compound--Uses of Collodion-Cotton--Celluloid--
Manufacture, &c.--Nitro-Starch, Nitro-Jute, and Nitro-Mannite.
~The Nitro-Celluloses.~--The substance known as cellulose forms the
groundwork of vegetable tissues. The cellulose of the woody parts of
plants was at one time supposed to be a distinct body, and was called
lignine, but they are now regarded as identical. The formula of cellulose
is (C_{6}H_{10}O_{6})_{X}, and it is generally assumed that the molecular
formula must be represented by a multiple of the empirical formula,
C_{12}H_{20}O_{10} being often regarded as the minimum. The assumption is
based on the existence of a penta-nitrate and the insoluble and colloidal
nature of cellulose. Green (_Zeit. Farb. Text. Ind._, 1904, 3, 97)
considers these reasons insufficient, and prefers to employ the single
formula C_{6}H_{10}O_{5}. Cellulose can be extracted in the pure state,
from young and tender portions of plants by first crushing them, to
rupture the cells, and then extracting with dilute hydrochloric acid,
water, alcohol, and ether in succession, until none of these solvents
remove anything more. Fine paper or cotton wool yield very nearly pure
cellulose by similar treatment.
Cellulose is a colourless, transparent mass, absolutely insoluble in
water, alcohol, or ether. It is, however, soluble in a solution of
cuprammoniac solution, prepared from basic carbonate or hydrate of copper
and aqueous ammonia. The specific gravity of cellulose is 1.25 to 1.45.
According to Schulze, its elementary composition is expressed by the
percentage numbers:--
Carbon 44.0 per cent. 44.2 per cent.
Hydrogen 6.3 " 6.4 "
Oxygen 49.7 " 49.4 "
These numbers represent the composition of the ash free cellulose. Nearly
all forms of cellulose, however, contain a small proportion of mineral
matters, and the union of these with the organic portion of the fibre or
tissue is of such a nature that the ash left on ignition preserves the
form of the original. "It is only in the growing point of certain young
shoots that the cellulose tissue is free from mineral constituents"
(Hofmeister).
Cellulose is a very inert body. Cold concentrated sulphuric acid causes it
to swell up, and finally dissolves it, forming a viscous solution.
Hydrochloric acid has little or no action, but nitric acid has, and forms
a series of bodies known as nitrates or nitro-celluloses. Cellulose has
some of the properties of alcohols, among them the power of forming
ethereal salts with acids. When cellulose in any form, such as cotton, is
brought into contact with strong nitric acid at a low temperature, a
nitrate or nitro product, containing nitryl, or the NO_{2} group, is
produced. The more or less complete replacement of the hydroxylic hydrogen
by NO_{2} groups depends partly on the concentration of the nitric acid
used, partly on the duration of the action. If the most concentrated
nitric and sulphuric acids are employed, and the action allowed to proceed
for some considerable time, the highest nitrate, known as hexa-nitro-
cellulose or gun-cotton, C_{12}H_{14}O_{4}(O.NO_{2})_{6}, will be formed;
but with weaker acids, and a shorter exposure to their action, the tetra
and penta and lower nitrates will be formed.[A]
[Footnote A: The paper by Prof. Lunge, _Jour. Amer. Chem. Soc._, 1901,
23[8], 527-579, contains valuable information on this subject.]
Besides the nitrate, A. Luck[A] has proposed to use other esters of
cellulose, such as the acetate, benzoate, or butyrate. It is found that
cellulose acetate forms with nitro-glycerine a gelatinous body without
requiring the addition of a solvent. A sporting powder is proposed
composed of 75 parts of cellulose nitrate (13 per cent. N.) mixed with 13
parts of cellulose acetate.
[Footnote A: Eng. Pat. 24,662, 22nd November 1898.]
The discovery of gun-cotton is generally attributed to Schönbein (1846),
but Braconnot (in 1832) had previously nitrated starch, and six years
later Pelouse prepared nitro-cotton and various other nitro bodies, and
Dumas nitrated paper, but Schönbein was apparently the first chemist to
use a mixture of strong nitric and sulphuric acids. Many chemists, such as
Piobert in France, Morin in Russia, and Abel in England, studied the
subject; but it was in Austria, under the auspices of Baron Von Lenk, that
the greatest progress was made. Lenk used cotton in the form of yarn, made
up into hanks, which he first washed in a solution of potash, and then
with water, and after drying dipped them in the acids. The acid mixture
used consisted of 3 parts by weight of sulphuric to 1 part of nitric acid,
and were prepared some time before use. The cotton was dipped one skein at
a time, stirred for a few minutes, pressed out, steeped, and excess of
acid removed by washing with water, then with dilute potash, and finally
with water. Von Lenk's process was used in England at Faversham (Messrs
Hall's Works), but was given up on account of an explosion (1847).
Sir Frederick Abel, working at Stowmarket and Waltham Abbey, introduced
several very important improvements into the process, the chief among
these being pulping. Having traced the cause of its instability to the
presence of substances caused by the action of the nitric acid on the
resinous or fatty substances contained in the cotton fibre, he succeeded
in eliminating them, by boiling the nitro-cotton in water, and by a
thorough washing, after pulping the cotton in poachers.
Although gun-cottons are generally spoken of as nitro-celluloses, they are
more correctly described as cellulose nitrates, for unlike nitro bodies of
other series, they do not yield, or have not yet done so, amido bodies, on
reduction with nascent hydrogen.[A] The equation of the formation of
gun-cotton is as follows:--
2(C_{6}H_{10}O_{5}) + 6HNO_{3} = C_{12}H_{14}O_{4}(NO_{3})_{6} + 6OH_{2}.
Cellulose. Nitric Acid. Gun-Cotton. Water.
The sulphuric acid used does not take part in the reaction, but its
presence is absolutely essential to combine with the water set free, and
thus to prevent the weakening of the nitric acid. The acid mixture used at
Waltham Abbey consists of 3 parts by weight of sulphuric acid of 1.84
specific gravity, and 1 part of nitric acid of 1.52 specific gravity. The
same mixture is also used at Stowmarket (the New Explosive Company's
Works). The use of weaker acids results in the formation of collodion-
cotton and the lower nitrates generally.
[Footnote A: "Cellulose," by Cross and Bevan, ed. by W.R. Hodgkinson, p.
9.]
The nitrate which goes under the name of gun-cotton is generally supposed
to be the hexa-nitrate, and to contain 14.14 per cent. of nitrogen; but a
higher percentage than 13.7 has not been obtained from any sample. It is
almost impossible (at any rate upon the manufacturing scale) to make pure
hexa-nitro-cellulose or gun-cotton; it is certain to contain several per
cents. of the soluble forms, i.e., lower nitrates. It often contains as
much as 15 or 16 per cent., and only from 13.07[A] to 13.6 per cent. of
nitrogen.
[Footnote A: Mr J.J. Sayers, in evidence before the court in the "Cordite
Case," says he found 15.2 and 16.1 per cent. soluble cotton, and 13.07 and
13.08 per cent. nitrogen in two samples of Waltham Abbey gun-cotton.]
A whole series of nitrates of cellulose are supposed to exist, the highest
member being the hexa-nitrate, and the lowest the mono-nitrate. Gun-cotton
was at one time regarded as the tri-nitrate, and collodion-cotton as the
di-nitrate and mono-nitrate, their respective formula being given as
follows:--
Mono-nitro-cellulose C_{6}H_{9}(NO_{2})O_{5} = 6.763 per cent. nitrogen.
Di-nitro-cellulose C_{6}H_{8}(NO_{2})_{2}O_{5} = 11.11 " "
Tri-nitro-cellulose C_{6}H_{7}(NO_{2})_{3}O_{5} = 14.14 " "
But gun-cotton is now regarded as the hexa-nitrate, and collodion-cotton
as a mixture of all the other nitrates. In fact, chemists are now more
inclined to divide nitro-cellulose into the soluble and insoluble forms,
the reason being that it is quite easy to make a nitro-cellulose entirely
soluble in a mixture of ether-alcohol, and yet containing as high a
percentage of nitrogen as 12.6; whereas the di-nitrate[A] should
theoretically only contain 11.11 per cent. On the other hand, it is not
possible to make gun-cotton with a higher percentage of nitrogen than
about 13.7, even when it does not contain any nitro-cotton that is soluble
in ether-alcohol.[B] The fact is that it is not at present possible to
make a nitro-cellulose which shall be either entirely soluble or entirely
insoluble, or which will contain the theoretical content of nitrogen to
suit any of the above formulæ for the cellulose nitrates. Prof. G. Lunge
gives the following list of nitration products of cellulose:--
[Footnote A: The penta-nitrate C_{12}H_{15}O_{5}(NO_{3})_{5} = 12.75 per
cent. nitrogen.]
[Footnote B: In the Cordite Trial (1894) Sir F.A. Abel said, "Before 1888
there was a broad distinction between soluble and insoluble nitro-
cellulose, collodion-cotton being soluble (in ether-alcohol) and
gun-cotton insoluble." Sir H.E. Roscoe, "That he had been unable to make a
nitro-cotton with a higher nitrogen content than 13.7." And Professor G.
Lunge said, "Gun-cotton always contained soluble cotton, and _vice
versa_." These opinions were also generally confirmed by Sir E. Frankland,
Sir W. Crookes, Dr Armstrong, and others.]
Dodeca-nitro-cellulose C_{24}H_{28}O_{20}(NO_{2})_{12} = 14.16 per cent.
nitrogen. (= old tri-nitro-cellulose)
Endeca-nitro-cellulose C_{24}H_{29}O_{20}(NO_{2})_{11} = 13.50 per cent.
nitrogen.
Deca-nitro-cellulose C_{24}H_{30}O_{20}(NO_{2})_{10} = 12.78 per cent.
nitrogen.
Ennea-nitro-cellulose C_{24}H_{31}O_{20}(NO_{2})_{9} = 11.98 per cent.
nitrogen.
Octo-nitro-cellulose C_{24}H_{32}O_{20}(NO_{2})_{8} = 11.13 per cent.
nitrogen. (= old di-nitro-cellulose)
Hepta-nitro-cellulose C_{24}H_{33}O_{20}(NO_{2})_{7} = 10.19 per cent.
nitrogen.
Hexa-nitro-cellulose C_{24}H_{34}O_{20}(NO_{2})_{6} = 9.17 per cent.
nitrogen.
Penta-nitro-cellulose C_{24}H_{35}O_{20}(NO_{2})_{5} = 8.04 per cent.
nitrogen.
Tetra-nitro-cellulose C_{24}H_{36}O_{20}(NO_{2})_{4} = 6.77 per cent.
nitrogen. (= old mono-nitro-cellulose)
It is not unlikely that a long series of nitrates exists. It is at any
rate certain that whatever strength of acids may be used, and whatever
temperature or other conditions may be present during the nitration, that
the product formed always consists of a mixture of the soluble and
insoluble nitro-cellulose.
Theoretically 100 parts of cotton by weight should produce 218.4 parts of
gun-cotton, but in practice the yield is a good deal less, both in the
case of gun-cotton or collodion-cotton. In speaking of soluble and
insoluble nitro-cellulose, it is their behaviour, when treated with a
solution consisting of 2 parts ether and 1 of alcohol, that is referred
to. There is, however, another very important difference, and that is
their different solubility in nitro-glycerine. The lower nitrates or
soluble form is soluble in nitro-glycerine under the influence of heat, a
temperature of about 50° C. being required. At lower temperatures the
dissolution is very imperfect indeed; and after the materials have been
left in contact for days, the threads of the cotton can still be
distinguished. The insoluble form or gun-cotton is entirely _insoluble_ in
nitro-glycerine. It can, however, be made to dissolve[A] by the aid of
acetone or acetic ether. Both or rather all the forms of nitro-cellulose
can be dissolved in acetone or acetic ether. They also dissolve in
concentrated sulphuric acid, and the penta-nitrate in nitric acid at about
80° or 90° C.
[Footnote A: Or rather to form a transparent jelly.]
The penta-nitrate may be obtained in a pure state by the following
process, devised by Eder:--The gun-cotton is dissolved in concentrated
nitric acid at 90° C., and reprecipitated by the addition of concentrated
sulphuric acid. After cooling to 0° C., and mixing with a larger volume of
water, the precipitated nitrate is washed with water, then with alcohol,
dissolved in ether-alcohol, and again precipitated with water, when it is
obtained pure. This nitrate is soluble in ether-alcohol, and slightly in
acetic acid, easily in acetone, acetic ether, and methyl-alcohol,
insoluble in alcohol. Strong potash (KOH) solution converts into the
di-nitrate C_{12}H_{18}O_{8}(NO_{3})_{2}. The hexa-nitrate is not soluble
in acetic acid or methyl-alcohol.
The lower nitrates known as the tetra- and tri-nitrates are formed
together when cellulose is treated with a mixture of weak acids, and
allowed to remain in contact with them for a very short time (twenty
minutes). They cannot be separated from one another, as they all dissolve
equally in ether-alcohol, acetic ether, acetic acid, methyl-alcohol,
acetone, amyl acetate, &c.
As far as the manufacture of explosive bodies is concerned, the two forms
of nitro-cellulose used and manufactured are gun-cotton or the hexa-
nitrate (once regarded as tri-nitro-cellulose), which is also known as
insoluble gun-cotton, and the soluble form of gun-cotton, which is also
known as collodion, and consists of a mixture of several of the lower
nitrates. It is probable that it chiefly consists, however, of the next
highest nitrate to gun-cotton, as the theoretical percentage of nitrogen
for this body,. the penta-nitrate, is 12.75 per cent., and analyses of
commercial collodion-cotton, entirely soluble in ether-alcohol, often give
as high a percentage as 12.6.
We shall only describe the manufacture of the two forms known as soluble
and insoluble, and shall refer to them under their better known names of
gun-cotton and collodion-cotton. The following would, however, be the
formulæ[A] and percentage of nitrogen of the complete series:--
Hexa-nitro-cellulose C_{12}H_{14}O_{4}(NO_{3})_{6} 14.14 per cent.
nitrogen.
Penta-nitro-cellulose C_{12}H_{15}O_{5}(NO_{3})_{5} 12.75 per cent.
nitrogen.
Tetra-nitro-cellulose C_{12}H_{16}O_{6}(NO_{3})_{4} 11.11 per cent.
nitrogen.
Tri-nitro-cellulose C_{12}H_{17}O_{7}(NO_{3})_{3} 9.13 per cent.
nitrogen.
Di-nitro-cellulose C_{12}H_{18}O_{8}(NO_{3})_{2} 7.65 per cent.
nitrogen.
Mono-nitrocellulose C_{12}H_{19}O_{9}(NO_{3}) 3.80 per cent.
nitrogen.
[Footnote A: Berthelot takes C_{24}H_{40}O_{20} as the formula of
cellulose; and M. Vieille regards the highest nitrate as
(C_{24}H_{18}(NO_{3}H)_{11}O_{9}). _Compt. Rend._, 1882, p. 132.]
~Properties of Gun-Cotton.~--The absolute density of gun-cotton is 1.5.
When in lumps its apparent density is 0.1; if twisted into thread, 0.25;
when subjected, in the form of pulp, to hydraulic pressure, 1.0 to 1.4.
Gun-cotton preserves the appearance of the cotton from which it is made.
It is, however, harsher to the touch; it is only slightly hygroscopic (dry
gun-cotton absorbs 2 per cent. of moisture from the air). It possesses the
property of becoming electrified by friction. It is soluble in acetic
ether, amyl acetate, and acetone, insoluble in water, alcohol, ether,
ether-alcohol, methyl-alcohol, &c. It is very explosive, and is ignited by
contact with an ignited body, or by shock, or when it is raised to a
temperature of 172° C. It burns with a yellowish flame, almost without
smoke, and leaves little or no residue. The volume of the gases formed is
large, and consists of carbonic acid, carbonic oxide, nitrogen, and water
gas. Compressed gun-cotton when ignited often explodes when previously
heated to 100° C.
Gun-cotton kept at 80° to 100° C. decomposes slowly, and sunlight causes
it to undergo a slow decomposition. It can, however, be preserved for
years without undergoing any alteration. It is very susceptible to
explosions by influence. For instance, a torpedo, even placed at a long
distance, may explode a line of torpedoes charged with gun-cotton. The
velocity of the propagation of the explosion in metallic tubes filled with
pulverised gun-cotton has been found to be from 5,000 to 6,000 mms. per
second in tin tubes, and 4,000 in leaden tubes (Sebert).
Gun-cotton loosely exposed in the open air burns eight times as quickly as
powder (Piobert). A thin disc of gun-cotton may be fired into from a rifle
without explosion; but if the thickness of the disc be increased, an
explosion may occur. The effect of gun-cotton in mines is very nearly the
same as that of dynamite for equal weights. It requires, however, a
stronger detonator, and it gives rise to a larger quantity of carbonic
oxide gas. Gun-cotton should be neutral to litmus, and should stand the
Government heat test--temperature of 150° F. for fifteen minutes (see page
249). In the French Navy gun-cotton is submitted to a heat test of 65° C.
(= 149° F.) for eleven minutes. It should contain as small a percentage of
soluble nitro-cotton and of non-nitrated cotton as possible.
The products of perfectly detonated gun-cotton may be expressed by the
following equation:--
2C_{12}H_{14}O_{4}(NO_{3})_{6} = 18CO + 6CO_{2} + 14H_{2}O + 12N.
It does not therefore contain sufficient oxygen for the complete
combustion of its carbon. It is for this reason that when used for mining
purposes a nitrate is generally added to supply this defect (as, for
instance, in tonite). It tends also to prevent the evolution of the
poisonous gas, carbonic oxide. The success of the various gelatine
explosives is due to this fact, viz., that the nitro-glycerine has an
excess of oxygen, and the nitro-cotton too little, and thus the two
explosives help one another.
In practice the gases resulting from the explosion of gun-cotton are--
Carbonic oxide, 28.55; carbonic acid, 19.11; marsh gas (CH_{4}), 11.17;
nitric oxide, 8.83; nitrogen, 8.56; water vapour, 21.93 per cent. The late
Mr E.O. Brown, of Woolwich Arsenal, discovered that perfectly wet and
uninflammable compressed gun-cotton could be easily detonated by the
detonation of a priming charge of the dry material in contact with it.
This rendered the use of gun-cotton very much safer for use as a military
or mining explosive.
As a mining explosive, however, gun-cotton is now chiefly used under the
form of tonite, which is a mixture of half gun-cotton and half barium
nitrate. This material is sometimes spoken of as "nitrated gun-cotton."
The weight of gun-cotton required to produce an equal effect either in
heavy ordnance or in small arms is to the weight of gunpowder in the
proportion of 1 to 3, i.e., an equal weight of gun-cotton would produce
three times the effect of gunpowder. Its rapidity of combustion, however,
requires to be modified for use in firearms. Hence the lower nitrates are
generally used, or such compounds as nitro-lignose, nitrated wood, &c.,
are used.
The initial pressure produced by the explosion of gun-cotton is very
large, equal to 18,135 atmospheres, and 8,740 kilogrammes per square
centimetre for 1 kilo., the heat liberated being 1,075 calories (water
liquid), or 997.7 cals. (water gaseous), but the quantity of heat
liberated changes with the equation of decomposition. According to
Berthelot,[A] the heat of formation of collodion-cotton is 696 cals. for
1,053 grms., or 661 cals. for 1 kilo. The heat liberated in the total
combustion of gun-cotton by free oxygen at constant pressure is 2,633
cals. for 1,143 grms., or for 1 kilo. gun-cotton 2,302 cals. (water
liquid), or 2,177 cals. (water gaseous). The heat of decomposition of gun-
cotton in a closed vessel, found by experiment at a low density of charge
(0.023), amounts to 1,071 cals. for 1 kilo. of the substance, dry and free
from ash. To obtain the maximum effect of gun-cotton it must be used in a
compressed state, for the initial pressures are thereby increased. Wet
gun-cotton s much less sensitive to shock than dry. Paraffin also reduces
its liability to explode, so also does camphor.
[Footnote A: "Explosives and their Power," trans. by Hake and M'Nab.]
The substance known as celluloid, a variety of nitro-cellulose nearly
corresponding to the formula C_{24}H_{24}(NO_{3}H)_{8}O_{12}, to which
camphor and various inert substances are added, so as to render it
non-sensitive to shock, may be worked with tools, and turned in the lathe
in the same manner as ivory, instead of which material celluloid is now
largely used for such articles as knife handles, combs, &c. Celluloid is
very plastic when heated towards 150° C., and tends to become very
sensitive to shock, and in large quantities might become explosive during
a fire, owing to the general heating of the mass, and the consequent
evaporation of the camphor. When kept in the air bath at 135° C.,
celluloid decomposes quickly. In an experiment (made by M. Berthelot) in a
closed vessel at 135° C., and the density of the charge being 0.4, it
ended in exploding, developing a pressure of 3,000 kilos. A large package
of celluloid combs also exploded in the guard's van on one of the German
railways a few years ago. Although it is not an explosive under ordinary
circumstances, or even with a powerful detonator, considerable care should
be exercised in its manufacture.
~The Manufacture of Gun-Cotton.~--The method used for the manufacture of
gun-cotton is that of Abel (Spec. No. 1102, 20. 4. 65). It was worked out
chiefly at Stowmarket[A] and Waltham Abbey,[B] but has in the course of
time undergone several alterations. These modifications have taken place,
however, chiefly upon the Continent, and relate more to the apparatus and
machinery used than to any alteration in the process itself. The form of
cellulose used is cotton-waste,[C] which consists of the clippings and
waste material from cotton mills. After it has been cleaned and purified
from grease, oil, and other fatty substances by treatment with alkaline
solutions, it is carefully picked over, and every piece of coloured cotton
rag or string carefully removed. The next operation to which it is
submitted has for its object the opening up of the material. For this
purpose it is put through a carding machine, and afterwards through a
cutting machine, whereby it is reduced to a state suitable for its
subsequent treatment with acids, that is, it has been cut into short
lengths, and the fibres opened up and separated from one another.
[Footnote A: The New Explosive Co. Works.]
[Footnote B: Royal Gunpowder Factory.]
[Footnote C: Costs from £10 to £25 a ton. In his description of the
"Preparation of Cotton-waste for the Manufacture of Smokeless Powder," A.
Hertzog states that the German military authorities require a cotton which
when thrown into water sinks in two minutes; when nitrated, does not
disintegrate; when treated with ether, yields only 0.9 per cent. of fat;
and containing only traces of chlorine, lime, magnesia, iron, sulphuric
acid, and phosphoric acid. If the cotton is very greasy, it must be first
boiled with soda-lye under pressure, washed, bleached with chlorine,
washed, treated with sulphuric acid or HCl, again washed, centrifugated,
and dried; if very greasy indeed a preliminary treatment with lime-water
is desirable. See also "Inspection of Cotton-Waste for Use in the
Manufacture of Gun-cotton," by C.E. Munro, _Jour. Am. Chem. Soc._, 1895,
17, 783.]
~Drying the Cotton.~--This operation is performed in either of two ways.
The cotton may either be placed upon shelves in a drying house, through
which a current of hot air circulates, or dried in steam-jacketed
cylinders. It is very essential that the cotton should be as dry as
possible before dipping in the acids, especially if a wholly "insoluble"
nitro-cellulose is to be obtained. After drying it should not contain more
than 0.5 per cent. of moisture, and less than this if possible. The more
general method of drying the cotton is in steam-jacketed tubes, i.e.,
double cylinders of iron, some 5 feet long and 1-1/2 foot wide. The cotton
is placed in the central chamber (Fig. 10), while steam is made to
circulate in the surrounding jacket, and keeps the whole cylinder at a
high temperature (steam pipes may be coiled round the outside of an iron
tube, and will answer equally well). By means of a pipe which communicates
with a compressed air reservoir, a current of air enters at the bottom,
and finds its way up through the cotton, and helps to remove the moisture
that it contains. The raw cotton generally contains about 10 per cent. of
moisture and should be dried until it contains only 1/2 per cent. or less.
For this it will generally have to remain in the drying cylinder for about
five hours. At the end of that time a sample should be taken from the
_top_ of the cylinder, and dried in the water oven (100° C.[A]) for an
hour to an hour and a half, and re-weighed, and the moisture then
remaining in it calculated.
[Footnote A: It is dried at 180° C. at Waltham Abbey, in a specially
constructed drying chamber.]
[Illustration: FIG. 10.--COTTON DRIER.]
It is very convenient to have a large copper water oven, containing a lot
of small separate compartments, large enough to hold about a handful of
the cotton, and each compartment numbered, and corresponding to one of the
drying cylinders. The whole apparatus should be fixed against the wall of
the laboratory, and may be heated by bringing a small steam pipe from the
boiler-house. It is useful to have a series of copper trays, about 3
inches by 6 inches, numbered to correspond to the divisions in the steam
oven, and exactly fitting them. These trays can then be taken by a boy to
the drying cylinders, and a handful of the cotton from each placed in
them, and afterwards brought to the laboratory and weighed (a boy can do
this very well), placed in their respective divisions of the oven, and
left for one to one and a half hours, and re-weighed.
When the cotton is found to be dry the bottom of the drying cylinder is
removed, and the cotton pushed out from the top by means of a piece of
flat wood fixed on a broom-handle. It is then packed away in galvanised-
iron air-tight cases, and is ready for the next operation. At some works
the cotton is dried upon shelves in a drying house through which hot air
circulates, the shelves being of canvas or of brass wire netting. The hot
air must pass under the shelves and through the cotton, or the process
will be a very slow one.
~Dipping and Steeping.~--The dry cotton has now to be nitrated. This is
done by dipping it into a mixture of nitric and sulphuric acids. The acids
used must be strong, that is, the nitric acid must be at least of a
gravity of 1.53 to 1.52, and should contain as little nitric oxide as
possible. The sulphuric acid must have a specific gravity of 1.84 at 15°
C., and contain about 97 per cent. of the mono-hydrate (H_{2}SO_{4}). In
fact, the strongest acids obtainable should be used when the product
required is gun-cotton, i.e., the highest nitrate.
The sulphuric acid takes no part in the chemical reaction involved, but is
necessary in order to combine with the water that is liberated in the
reaction, and thus to maintain the strength of the nitric acid. The
reaction which takes place is the following:--
2(C_{6}H_{10}O_{5}) + 6HNO_{3} = C_{12}H_{14}(NO_{3})_{6} + 6 H_{2}O.
324 378 = 594 108.
Cellulose. Gun-Cotton.
Theoretically,[A] therefore, 1 part of cellulose should form 1.8 part of
gun-cotton. Practically, however, this is never obtained, and 1.6 lb. from
1 lb. of cellulose is very good working. The mixture of acids used is
generally 1 to 3, or 25 per cent. nitric acid to 75 per cent. sulphuric
acid.
[Footnote A: (594 x 1)/324= 1.83.]
[Illustration: FIG. 11.--TANK FOR DIPPING COTTON.]
[Illustration: FIG. 12.--THE COOLING PITS.]
The dipping is done in cast-iron tanks (Fig. 11), a series of which is
arranged in a row, and cooled by a stream of cold water flowing round
them. The tanks hold about 12 gallons, and the cotton is dipped in
portions of 1 lb. at a time. It is thrown into the acids, and the workman
moves it about for about three minutes with an iron rabble. At the end of
that time he lifts it up on to an iron grating, just above the acids,
fixed at the back of the tank, where by means of a movable lever he gently
squeezes it, until it contains about ten times its weight of acids (the 1
lb. weighs 10 lbs.). It is then transferred to earthenware pots to steep.
[Illustration: FIG. 13.--COTTON STEEPING POT.]
~Steeping.~--The nitrated cotton, when withdrawn from the dipping tanks,
and still containing an excess of acids, is put into earthenware pots of
the shape shown in Figs. 12 and 13. The lid is put on, and the pots placed
in rows in large cooling pits, about a foot deep, through which a stream
of water is constantly flowing. These pits form the floor of the steeping
house. The cotton remains in these pots for a period of forty-eight hours,
and must be kept cool. Between 18° and 19° C. is the highest temperature
desirable, but the cooler the pots are kept the better. At the end of
forty-eight hours the chemical reaction is complete, and the cotton is or
should be wholly converted into nitro-cellulose; that is, there should be
no unnitrated cotton.
[Illustration: FIG. 14.--HYDRO-EXTRACTOR.]
~Whirling Out the Acid.~--The next operation is to remove the excess of
acid. This is done by placing the contents of two or three or more pots
into a centrifugal hydro-extractor (Fig. 14), making 1,000 to 1,500
revolutions per minute. The hydro-extractor consists of a machine with
both an inner cylinder and an outer one, both revolving in concert and
driving outwardly the liquid to the chamber, from which it runs away by a
discharge pipe. The wet cotton is placed around the inner cone. The
cotton, when dry, is removed, and at once thrown into a large tank of
water, and the waste acids are collected in a tank.[A]
[Footnote A: Care must be taken in hot weather that the gun-cotton does
not fire, as it does sometimes, directly the workman goes to remove it
after the machine is stopped. It occurs more often in damp weather. Dr
Schüpphaus, of Brooklyn, U.S.A., proposes to treat the waste acids from
the nitration of cellulose by adding to them sulphuric anhydride and
nitric acid. The sulphuric anhydride added converts the water liberated
from the cellulose into sulphuric acid.]
~Washing.~--The cotton has now to be carefully washed. This is done in a
large wooden tank filled with water. If, however, a river or canal runs
through the works, a series of wooden tanks, the sides and bottoms of
which are pierced with holes, so as to allow of the free circulation of
water, should be sunk into a wooden platform that overhangs the surface of
the river in such a way that the tanks are immersed in the water, and of
course always full. During the time that the cotton is in the water a
workman turns it over constantly with a wooden paddle. A stream of water,
in the form of a cascade, should be allowed to fall into these tanks. The
cotton may then be thrown on to this stream of water, which, falling some
height, at once carries the cotton beneath the surface of the water. This
proceeding is necessary because the cotton still retains a large excess of
strong acids, and when mixed with water gives rise to considerable heat,
especially if mixed slowly with water. After the cotton has been well
washed, it is again wrung out in a centrifugal machine, and afterwards
allowed to steep in water for some time.
[Illustration: FIG. 15_a_.--THE BEATER FOR GUN-COTTON.]
~Boiling.~--The washed cotton is put into large iron boilers with plenty
of water, and boiled for some time at 100° C. In some works lead-lined
tanks are used, into which a steam pipe is led. The soluble impurities of
unstable character, to which Sir F.A. Abel traced the liability of gun-
cotton to instability, are thereby removed. These impurities consist of
the products formed by the action of nitric acid on the fatty and resinous
substances contained in the cotton fibres. The water in the tanks should
be every now and again renewed, and after the first few boilings the water
should be tested with litmus paper until they are no longer found to be
acid.
[Illustration: FIG. 15_b_.--WHEEL OF BEATER.]
~Pulping.~--The idea of pulping is also due to Abel. By its means a very
much more uniform material is obtained. The process is carried out in an
apparatus known as a "Beater" or "Hollander" (Fig. 15, _a, b_). It
consists of a kind of wooden tank some 2 or 3 feet deep of an oblong
shape, in which a wheel carrying a series of knives is made to revolve,
the floor of the tank being sloped up so as to almost touch the revolving
wheels. This part of the floor, known as the "craw," is a solid piece of
oak, and a box of knives is fixed into it, against which the knives in the
revolving wheel are pressed. The beater is divided into two parts--the
working side, in which the cotton is cut and torn between the knife edges
in the revolving cylinder and those in the box; and the running side, into
which the cotton passes after passing under the cylinder. The wheel is
generally boxed in to prevent the cotton from being thrown out during its
revolution. The cotton is thus in constant motion, continually travelling
round, and passing between the knives in the revolving cylinder and those
in the box fixed in the wooden block beneath it. The beater is kept full
of water, and the cotton is gradually reduced to a condition of pulp. The
wheel revolves at the rate of 100 to 150 times a minute.
[Illustration: FIG. 16_a_.--POACHER FOR WASHING GUN-COTTON.]
[Illustration: FIG. 16_b_.--PLAN OF THE POACHER.]
[Illustration: FIG. 16_c_.--ANOTHER FORM OF POACHER.]
When the gun-cotton is judged to be sufficiently fine, the contents of the
beater are run into another very similar piece of machinery, known as the
"poacher" (Fig. 16, _a, b, c_), in which the gun-cotton is continuously
agitated together with a large quantity of water, which can be easily run
off and replaced as often as required. When the material is first run into
the poacher from the beater, the water with which it is then mixed is
first run away and clean water added. The paddle wheel is then set in
motion, and at intervals fresh water is added. There is a strainer at the
bottom of the poacher which enables the water to be drawn off without
disturbing the cotton pulp. After the gun-cotton has been in the poacher
for some time, a sample should be taken by holding a rather large mesh
sieve in the current for a minute or so. The pulp will thus partly pass
through and partly be caught upon the sieve, and an average sample will be
thus obtained. The sample is squeezed out by hand, bottled, and taken to
the laboratory to be tested by the heat test for purity. It first,
however, requires to be dried. This is best done by placing the sample
between coarse filter paper, and then putting it under a hand-screw press,
where it can be subjected to a tolerably severe pressure for about three
minutes. It is then rubbed up very finely with the hands, and placed upon
a paper tray, about 6 inches by 4-1/2 inches, which is then placed inside
a water oven upon a shelf of coarse wire gauze, the temperature of the
oven being kept as near as possible to 120° F. (49° C.), the gauze shelves
in the oven being kept 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 laboratory (away from acid fumes) 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.
Twenty grains (1.296 grm.) are used for the test. (See Heat Test, page
249.)
If the gun-cotton sample removed from the poacher stands the heat test
satisfactorily, the machine is stopped, and the water drained off. The
cotton is allowed some little time to drain, and is then dug out by means
of wooden spades, and is then ready for pressing. The poachers hold about
2,000 lbs. of material, and as this represents the products of many
hundred distinct nitrating operations, a very uniform mixture is obtained.
Two per cent. of carbonate of soda is sometimes added, but it is not
really necessary if the cotton has been properly washed.
~Compressing Gun-Cotton.~--The gun-cotton, in the state in which it is
removed from the poacher, contains from 28 to 30 per cent. of water. In
order to remove this, the cotton has to be compressed by hydraulic power.
The dry compressed gun-cotton is packed in boxes containing 2,500 lbs. of
dry material. In order to ascertain how much of the wet cotton must be put
into the press, it is necessary to determine the percentage of water. This
may be done by drying 2,000 grains upon a paper tray (previously dried at
100° C.) in the water oven at 100° C. for three hours, and re-weighing and
calculating the percentage of water. It is then easy to calculate how much
of the wet gun-cotton must be placed in the hopper of the press in order
to obtain a block of compressed cotton of the required weight. Various
forms of presses are used, and gun-cotton is sent out either as solid
blocks, compressed discs, or in the form of an almost dry powder, in zinc-
lined, air-tight cases. The discs are often soaked in water after
compression until they have absorbed 25 per cent. of moisture.
[Illustration: FIG. 17.--OLD METHOD. 100 PIECES.]
[Illustration: FIG. 18.--NEW METHOD. ONE SOLID BLOCK.]
At the New Explosives Company's Stowmarket Works large solid blocks of
gun-cotton are pressed up under a new process, whereby blocks of gun-
cotton, for use in submarine mines or in torpedo warheads, are produced.
Large charges of compressed gun-cotton have hitherto been built up from a
number of suitably shaped charges of small dimensions (Fig. 17), as it has
been impossible to compress large charges in a proper manner. The
formation of large-sized blocks of gun-cotton was the invention of Mr A.
Hollings. Prior to the introduction of this method, 8 or 9 lbs. had been
the limit of weight for a block. This process has been perfected at the
Stowmarket factory, where blocks varying from the armour-piercing shell
charge of a few ounces up to blocks of compressed gun-cotton mechanically
true, weighing 4 to 5 cwts. for torpedoes or submarine mines, are now
produced. At the same time the new process ensures a uniform density
throughout the block, and permits of any required density, from 1.4
downwards, being attained; it is also possible exactly to regulate the
percentage of moisture, and to ensure its uniform distribution. The
maximum percentage of moisture depends, of course, upon the density. By
the methods of compression gun-cotton blocks hitherto employed, blocks of
a greater thickness than 2 inches, or of a greater weight than 9 lbs.,
could not be made, but with the new process blocks of any shape, size,
thickness, or weight that is likely to be required can be made readily and
safely. The advantages which are claimed for the process may be enumerated
as follows:--(1.) There is no space wasted, as in the case with built-up
charges, through slightly imperfect contact between the individual blocks,
and thus either a heavier charge--i.e., about 15 per cent. more gun-
cotton--can be got into the same space, or less space will be occupied by
a charge of a given weight. (2.) The metallic cases for solid charges may
be much lighter than for those built-up, since with the former their
function is merely to prevent the loss of moisture from wet gun-cotton, or
to prevent the absorption of moisture by dry gun-cotton. They can thus be
made lighter, as the solid charge inside will prevent deformation during
transport. With built-up charges the case must be strong enough to prevent
damage, either to itself or to the charge it contains. For many uses a
metal case, however light, may be discarded, and one of a thin waterproof
material substituted. (3.) The uniform density of charges made by this
process is very favourable to the complete and effective detonation of the
entire mass, and to the presence of the uniform amount of moisture in
every part of the charge. (4.) Any required density, from the maximum
downwards, may be obtained with ease, and any required amount of moisture
left in the charge. These points are of great importance in cases where,
like torpedo charges, it is essential to have the centre of gravity of the
charge in a predetermined position both vertically and longitudinally, and
the charge so fixed in its containing case that the centre of gravity
cannot shift. The difficulty of ensuring this with a large torpedo charge
built up from a number of discs and segments is well known. Even with
plain cylindrical or prismatic charges a marked saving in the process of
production is effected by this new system. The charges being in one block
they are more easily handled for the usual periodical examination, and
they do not break or chafe at the edges, as in the case of discs and cubes
in built-up charges. A general view of the press is given in Fig. 19. The
gun-cotton in a container is placed on a cradle fixed at an angle to the
press. The mould is swivelled round, and the charge pushed into it with a
rammer, and it is then swivelled back into position. The mould is made up
of a number of wedge pieces which close circumferentially on the enclosed
mass, which is also subjected to end pressure. Holes are provided for the
escape of water.
[Illustration: FIG. 19.--A 4-CWT. BLOCK OF GUN-COTTON BEING TAKEN FROM
HYDRAULIC PRESS.]
~The Waltham Abbey Process.~--At the Royal Gunpowder Factory, Waltham
Abbey, the manufacture of gun-cotton has been carried out for many years.
The process used differs but little from that used at Stowmarket. The
cotton used is of a good quality, it is sorted and picked over to remove
foreign matters, &c., and is then cut up by a kind of guillotine into
2-inch lengths. It is then dried in the following manner. The cotton is
placed upon an endless band, which conducts it to the stove, or drying
closet, a chamber heated by means of hot air and steam traps to about
180° F.; it falls upon a second endless band, placed below the first; it
travels back again the whole length of the stove, and so on until
delivered into a receptacle at the bottom of the farther end, where it is
kept dry until required for use. The speed at which the cotton travels is
6 feet per minute, and as the length of the band travelled amounts to 126
feet, the operation of drying takes twenty-one minutes. One and a quarter
lb. are weighed out and placed in a tin box; a truck, fitted to receive a
number of these boxes, carries it along a tramway to a cool room, where it
is allowed to cool.
~Dipping.~--Mixed acids are used in the proportion of 1 to 3, specific
gravity nitric acid 1.52, and sulphuric acid 1.84. The dipping tank is
made of cast iron, and holds 220 lbs. of mixed acids, and is surrounded on
three sides by a water space in order to keep it cool. The mixed acids are
stored in iron tanks behind the dipping tanks, and are allowed to cool
before use. During the nitration, the temperature of the mixed acids is
kept at 70° F., and the cotton is dipped in quantities of 1-1/2 lb. at a
time. It is put into a tin shoot at the back of the dipping tank, and
raked into the acids by means of a rabble. It remains in the acids for
five or six minutes, and is then removed to a grating at the back, pressed
and removed. After each charge of cotton is removed from the tank, about
14 lbs. of fresh mixed acids are added, to replace amount removed by
charge. The charge now weighs, with the acids retained by it, 15 lbs.; it
is now placed in the pots, and left to steep for at least twenty-four
hours, the temperature being kept as low as possible, to prevent the
formation of soluble cotton, and also prevent firing. The proportion of
soluble formed is likely to be higher in hot weather than cold. The pots
must be covered to prevent the absorption of moisture from the air, or the
accidental entrance of water, which would cause decomposition, and
consequent fuming off, through the heat generated by the action of the
water upon the strong acids.
The excess of acids is now extracted by means of hydro-extractors, as at
Stowmarket. They are worked at 1,200 revolutions per minute, and whirled
for five minutes (10-1/2 lbs. of waste acids are removed from each charge
dipped). The charge is then washed in a very similar manner to that
previously described, and again wrung out in a centrifugal extractor
(1,200 revolutions per minute). The gun-cotton is now boiled by means of
steam in wooden tanks for eight hours; it is then again wrung out in the
extractors for three minutes, boiled for eight hours more, and again wrung
out; it is then sent to the beater and afterwards to the poacher. The
poachers hold 1,500 gals. each, or 18 cwt. of cotton. The cotton remains
six hours in the poachers. Before moulding, 500 gals. of water are run
into the poacher, and 500 gals. of lime water containing 9 lbs. of whiting
and 9 gals. of a caustic soda solution. This mixture is of such a strength
that it is calculated to leave in the finished gun-cotton from 1 to 2 per
cent. of alkaline matter.
By means of vacuum pressure, the pulp is now drawn off and up into the
stuff chest--a large cylindrical iron tank, sufficiently elevated on iron
standards to allow room for the small gauge tanks and moulding apparatus
below. It holds the contents of one poacher (18 cwt.), and is provided
with revolving arms to keep the pulp stirred up, so that it may be
uniformly suspended in water.
Recently a new process, invented by J.M. and W.T. Thomson (Eng. Pat. No.
8,278, 1903), has been introduced at the Waltham Abbey Factory. The object
of this invention is the removal of the acids of nitration from the
nitrated material after the action has been completed, and without the aid
of moving machinery, such as presses, rollers, centrifugals, and the like.
The invention consists in the manufacture of nitrated celluloses by
removing the acids from the nitrated cellulose directly by displacement
without the employment of either pressure or vacuum or mechanical
appliances of any kind, and at the same time securing the minimum dilution
of the acids. It was found that if water was carefully run on to the
surface of the acids in which the nitro-cellulose is immersed, and the
acids be slowly drawn off at the bottom of the vessel, the water displaces
the acid from the interstices of the nitro-cellulose without any
undesirable rise in temperature, and with very little dilution of the
acids. By this process almost the whole of the acid is recovered in a
condition suitable for concentration, and the amount of water required for
preliminary washing is very greatly reduced. The apparatus which is used
for the purpose consists of a cylindrical or rectangular vessel
constructed with a perforated false bottom and a cock at its lowest point
for running off the liquid. Means are also provided to enable the
displacing water to be run quietly on to the surface of the nitrating
acids.[A]
[Footnote A: In a further patent (Eng. Pat. 7,269, 1903, F.L. Natham),
J.M. Thomson and W.T. Thomson propose by use of alcohol to replace the
water, used in washing nitro-cellulose, and afterward to remove the
alcohol by pressing and centrifuging.]
The apparatus is shown in Fig. 2O, side elevation, and in Fig. 21 a plan
of the nitrating vessel and its accessories is given. In Fig. 20 is shown
in sectional elevation one of the trough devices for enabling liquids to
be added to those in the nitrating vessel without substantial disturbance.
[Illustration: FIG. 20.--SECTIONAL ELEVATION OF THOMSON'S APPARATUS, _a_,
Tank; _b_, False Bottom; _c_, Bottom; _c'_, Ribs; _d_, Draining Outlet;
_e_, Grid; _f_, Troughs, with Aprons _g_; _h_, Pipe, with Branches _h'_,
leading to Troughs, _f_; _k'_, Outlet Pipe of the Sulphuric Acid Tank _k_;
_l_, Water Supply Pipe; _m_, Pipe to supply of Nitrating Acids; _o_,
Perforations of Trough _f_; _p_, Cock to remove Acid.]
In carrying out this invention a rectangular lead-lined or earthenware
tank _a_ is employed, having a false bottom _b_, supported by ribs _c'_,
over the real bottom _c_, which slopes down to a draining outlet pipe _d_,
provided with a perforated grid or plate _e_, adapted to prevent choking
of the outlet. Suitably supported near the top of the vessel _a_ are
provided two troughs, _f_ having depending aprons _g_, a pipe _h_ has two
branches _h'_, leading to the troughs, _f_. This pipe _h_ is adapted to be
connected by a rubber pipe either to the outlet pipe _k'_ of the sulphuric
acid tank _k_ or the water supply pipe _l_. The nitrating acids are
supplied through the pipe _m_. A charge of mixed nitrating acids is
introduced into the vessel _a_ say up to the level _n_, and the dry
cellulose thrown into the acids in small quantities at a time, being
pushed under the surface in the usual way.
[Illustration: FIG. 21.--PLAN OF THOMSON'S APPARATUS, _a_, Tank; _b_,
False Bottom; _c'_, Ribs; _e_, Grid; _f_, Troughs; _g_, Aprons; _h_ and
_h'_, Pipes to Troughs _f_; _k_, Sulphuric Acid Tank; _m_, Pipe to
Nitrating Acids Tank; _o_, Perforations of Troughs; _p_, Cock to remove
Acid.]
A thin layer, say half an inch, of a suitable liquid, preferably sulphuric
acid, of a gravity not exceeding that of the waste acid to be produced, is
run carefully on the top of the acids by means of the troughs _f_, which
are perforated as shown at _o_, so that the sulphuric acid runs down the
aprons _g_, and floats on the nitrating acids. The whole is then allowed
to stand till nitration has been completed. Water is then supplied to the
troughs by way of the pipes _l_, _h_, and _h'_, and is allowed to float
very gently over the surface of the sulphuric acid, and when a sufficient
layer has been formed, the cock _p_ at the bottom of the apparatus is
opened, and the acid slowly drawn off, water being supplied to maintain
the level constant. It is found that the rate of displacement of the acids
is a factor which exerts a considerable influence on the properties of the
resulting nitro-cellulose, and affords a means of regulating the
temperature of displacement. A rate of displacement which has been found
suitable is about two inches in depth of the vessel per hour when treating
highly nitrated celluloses, but this rate may, in some cases, be
considerably increased. The flow of water at the top of the apparatus is
regulated so that a constant level is maintained. By this means the water
gradually and entirely displaces the acids from the interstices of the
nitro-cellulose, the line of separation between the acids and the water
being fairly sharply defined throughout. The flow of water is continued
until that issuing at the bottom is found to be free from all trace of
acid. The purification of the nitro-cellulose is then proceeded with as
usual, either in the same vessel or another.
In the process above described, the object of the introduction of a small
layer of sulphuric acid is mainly to prevent the fuming which would
otherwise take place, and is not essential, as it is found it can be
omitted without any deleterious effect. In order to use the mixed acids in
the most economical manner, the waste acid from a previous operation may
be used for a first nitration of the cellulose; being afterwards displaced
with fresh acids which carry the nitration to the required degree before
they are in turn displaced by water. The apparatus may be used merely for
the removal of the acid, in which case the nitration is carried out in
other vessels in the usual way, and the nitro-cellulose removed to the
displacement apparatus where it is just covered with waste acid, and the
displacement then proceeded with as above described. In some cases the
process is carried out in an ordinary nitrating centrifugal, using the
latter to effect preliminary drying after acid extraction. This gives a
great advantage over the usual method of working ordinary centrifugal
nitrating apparatus, because the acid being removed before the centrifugal
is run, practically all danger of firing therein disappears, and a greater
proportion of the waste acid is recovered.
In some cases the acids and water may be supplied by perforated pipes,
lying along the edges of the nitrating vessel, and these edges may, if
desired, be themselves made inclined, like the sides of the troughs _f_.
In the case of effecting nitration in centrifugals as above, the
displacing sulphuric acid and water may thus be supplied round the edges
of the machines, or removal troughs such as _f_ may be used. It will be
obvious that any inert liquid of suitable specific gravity may be used
instead of sulphuric acid, as a separation layer.
~Moulding.~--By means of the small measuring tank above referred to, the
gun-cotton pulp is drawn off from the stuff chest, and run into moulds of
the shapes and sizes required. Thence a large proportion of the water is
drawn off by means of tubes connected with the vacuum engine, the moulds
having bottoms of fine wire gauze, in order to prevent the pulp from
passing through. Hydraulic pressure of about 34 lbs. on the square inch is
then applied, which has the effect of compressing the pulp into a state in
which it has sufficient consistency to enable it to be handled with care,
and also expels a portion of the remaining water.
~Compressing.~--The moulded gun-cotton is now taken to the press house,
which is situated at some distance from the rest of the factory. Here the
moulds are subjected to powerful hydraulic pressure, from 5 to 6 tons per
square inch, and is compressed to one-third of its previous bulk. The
slabs or discs thus formed are kept under pressure for a short time, not
exceeding a minute and a half, to give the requisite density. It should,
when removed, be compact, and just sink in water, and should perceptibly
yield to the pressure of the fingers. There are perforations in the press
blocks, to allow of the escape of gases, if formed, by reason of
sufficient heat being generated. The men working the press are placed
under cover, behind strong rope mantlets having eye tubes which command a
view of the press.
~Packing.~--The finished slabs and discs are dipped into a solution of
soda and carbolic acid, and packed in special wood metal-lined cases. When
it is to be sent abroad, the metal lining, which is made of tinned copper,
is soldered down, but both the outer wooden and inner metal cases are
fitted with air-tight screw-plugs, so that when necessary water can be
added without unfastening the cases.
~Reworked gun-cotton~ does not make such good discs as new pulped gun-
cotton, probably because the fibrous tenacity of the gun-cotton has been
destroyed by the amount of pressure it has previously undergone, so that
when repulped it resembles fine dust, and a long time is required to press
it into any prescribed form. It is generally boiled for eight hours to
open up the fibre and remove alkali, then broken up by hand with wooden
mallets, pulped, and then used with fresh gun-cotton in the proportion of
1 to 5 parts.
~Manufacture at Le Bouchet.~--At Le Bouchet gun-cotton was made thus:--200
grms. of cotton were steeped for an hour in 2 litres of a mixture of 1
volume concentrated nitric and 2 volumes sulphuric acid. The cotton was
then removed and pressed, whereby 7/10ths of the waste acids was
recovered. After this it was washed for one to one and a half hours in
running water, strongly pressed again; allowed to lie for twenty-four
hours in wood-ash lye; then well washed in running water; pressed, and
finally dried on a wide linen sheet, through which was forced air heated
to 60° C. The average yield from 100 parts of cotton was 165 parts of gun-
cotton. The strong pressings of the gun-cotton, while still impregnated
with acids, caused subsequent washings to be difficult and laborious.
~Granulation of Gun-Cotton.~--Gun-cotton is often required in the
granulated form for use either alone or with some form of smokeless
powder. This is done under the patent of Sir Frederick Abel in the
following manner:--The gun-cotton from the poacher is placed in a
centrifugal machine, very similar to the hydro-extractors before
mentioned, and used for wringing out the acids. In this machine it loses
water until it only contains 33 per cent., and is at the same time reduced
to a more or less fibrous state. It is then taken to the granulating room,
where it is first passed through sieves or perforations, which break up
the mass into little pieces like shot. The material is then transferred to
a revolving drum made of wood or stout leather, which is kept constantly
revolving for some time. The material is occasionally sprinkled with
water. The drum in turning, of course, carries the granules partially
round with it, but the action of gravity causes them to descend constantly
to the lowest point, and thus to roll over one another continually. The
speed of the drum must not be too rapid. None of the granules must be
carried round by centrifugal force, but it must be fast enough to carry
them some little distance up the side of the drum. After removal from the
drum the granules are dried upon shelves in the drying house.
Gun-cotton is also dissolved in acetone or acetic ether until it has taken
the form of a jelly. It is then rolled into thin sheets, and when dry cut
up into little squares. In the manufacture of smokeless powders from
nitro-cellulose, nitro-lignine, &c., the various substances are mixed with
the gun-cotton or collodion-cotton before granulating.
~Collodion-Cotton.~--In the manufacture of collodion or soluble cotton the
finer qualities of cotton-waste are used and the acids used in the dipping
tanks are much weaker. The manufacture of collodion-cotton has become of
more importance than gun-cotton, by reason of its use for the manufacture
of the various forms of gelatine, such as gelatine dynamite, gelignite,
forcite, &c., and also on account of its extensive use in the manufacture
of many of the smokeless powders. It is also used for the manufacture of
"collodion," which is a solution of collodion-cotton in ether-alcohol; for
the preparation of celluloid, and many other purposes. It is less
explosive than gun-cotton, and consists of the lower nitrates of
cellulose. It is soluble in nitro-glycerine, and in a mixture of 2 parts
of ether and 1 of alcohol; also in acetone, acetic ether, and other
solvents. MM. Ménard and Domonte were the first to prepare a soluble gun-
cotton, and its investigation was carried on by Béchamp, who showed that
its properties and composition were different to those of gun-cotton.
~Manufacture.~--The cotton used is cotton-waste.[A] It is thought by some
that Egyptian cotton is preferable, and especially long fibre varieties.
The strength of the acids used is, however, of more importance than the
quality of the cotton. The percentage composition of the acid mixture
which gives the best results is as follows:--Nitric acid, 23 per cent.;
sulphuric acid, 66 per cent.; and water, 11 per cent; and has a specific
gravity of 1.712 (about). It can be made by mixing sulphuric acid of
specific gravity 1.84 with nitric acid of specific gravity 1.368 in the
proportions of 66 per cent. and 34 per cent. respectively. (The production
of the penta-nitro-cellulose is aimed at if the collodion-cotton is for
use as an explosive.) If the acids are much weaker than this, or potassium
nitrate and sulphuric acid is used, the lower nitrates will be formed. The
product, while being entirely soluble in ether-alcohol or nitro-glycerine,
will have a low nitrogen content, whereas a material with as high a
nitrogen as 12 or 12.6 is to be aimed at.
[Footnote A: Raw cotton is often used.]
The cotton should not be allowed to remain in the dipping tanks for more
than five minutes, and the acid mixture should be kept at a temperature of
28° C. or thereabouts; and the cotton should be removed after a few
minutes, and should not be pressed out, as in the case of gun-cotton, but
at once transferred to the pots and allowed to steep for forty-eight
hours. (Some prefer twenty-four hours, but there is more chance in this
case of the product containing non-nitrated cellulose.) When the nitration
is complete, the collodion-cotton is removed from the pots, and treated in
exactly the same manner as described under gun-cotton. The produce should
be entirely soluble in ether-alcohol and nitro-glycerine, and contain as
near 12.7 per cent. of nitrogen as possible. The theoretical nitrogen is
for the penta-nitro-cellulose 12.75 per cent. This will, however, seldom
if ever be obtained. The following are some of the results I have obtained
from different samples:--
Nitrogen.
(1.) (2.) (3.)
German make 11.64 11.48 11.49 per cent.
Stowmarket 12.57 12.60 11.22 "
Walsrode 11.61 12.07 11.99 "
Faversham 12.14 11.70 11.60 "
and the following was the analysis of a sample (No. 1) of German-made
collodion-cotton, which made very good blasting gelatine:--
_
Soluble cotton (collodion) 99.118 per cent.| Nitrogen = 11.64 per cent.
Gun-cotton 0.642 " _|
Non-nitrated cotton 0.240 "
Total ash 0.25 "
It should contain as little non-nitrated or unconverted cotton and as
little gun-cotton as possible, as they are both insoluble in nitro-
glycerol. The quality and composition of any sample of collodion-cotton
can be quickly inferred by determining the percentage of nitrogen by means
of the nitrometer and the use of the solubility test.[A] A high nitrogen
content coupled with a high solubility is the end to be aimed at; a high
nitrogen with a low solubility shows the presence of gun-cotton, and a low
nitrogen, together with a low solubility, the presence of unnitrated
cotton. Where complete solubility is essential and the percentage of
nitrogen less important, Dr Lunge recommends nitration with a mixture of
equal parts of sulphuric and nitric acids containing from 19 to 20 per
cent. of water.
[Footnote A: See Analysis of Explosives.]
Mr T.R. France claims to have invented some improvements in the
manufacture of soluble nitro-cellulose. His object has been to produce an
article as uniform as possible. His explanation of the imperfect action of
the acids is that, however uniform the mixed acids may be in strength and
proportions, and however carefully the operations of nitrating, &c., may
be conducted, there are variable elements found in different samples of
cotton. The cotton fibre has for its protection a glazed surface. It is
tubular and cellular in structure, and contains a natural semi-fluid
substance composed of oil or gum, which varies in nature according to the
nature of the soil upon which the cotton is grown. The tubes of the fibre
seem to be open at one end only when the fibre is of normal length. When,
therefore, the cotton is subjected to the action of the mixed acids, the
line of least resistance seems to be taken by them, viz., the insides of
the tubes constituting the fibre of the cotton, into which they are taken
by capillary attraction, and are subject to change as they progress, and
to the increased resistance from the oil or gum, &c., in their progress,
and therefore to modified action, the result of which is slower and slower
action, or chemical change. He also thinks it is possible that the power
of capillary attraction is balanced in the tubes by air contained therein,
after a little, sufficiently so to prevent the acids from taking full
effect. To get over this, Mr France uses his cotton in a fine state,
almost dust, in fact, and then nitrates in the usual mixture of acids at
40° to 90° F., the excess of acids being removed by pressure. He says he
does not find it necessary to wash this fine cotton dust in an alkaline
solution previous to nitration. His mixed acids consist of 8 parts HNO_{3}
= 42° B., and 12 parts H_{2}SO_{4} = 66° B., and he stirs in the dipping
tank for fifteen minutes, the temperature being 50° F. to 100° F., the
temperature preferred being 75° F.
~"Nitrated" Gun-Cotton.~--The nitrates that are or have been mixed with
gun-cotton in order to supply oxygen are potassium nitrate, ammonium
nitrate, and barium nitrate (tonite). The total combustion of gun-cotton
by potassium nitrate corresponds to the equation:--
10[C_{24}H_{18}(NO_{3}H)_{11}O_{9}] + 82KNO_{3} = 199CO_{2} +
41K_{2}CO_{3} + 145H_{2}O + 96N_{2},
or 828 grms. of nitrate for 1,143 grms. of gun-cotton, or 42 per cent.
nitrate and 58 per cent. gun-cotton. The explosive made at Faversham by
the Cotton Powder Company, and known as tonite No. 1, consists of very
nearly half gun-cotton and half barium nitrate. The relations by weight of
total combustion would be 51.6 of gun-cotton to 48.4 of barium nitrate.
The average composition of tonite I have found by analysis to be 51 per
cent. gun-cotton to 49 per cent. barium nitrate. The heat liberated is
practically the same as for an equivalent weight of KNO_{3}; but the
barium nitrate mixture weighs 2,223 grms. instead of 1,971 grms., or
one-eighth more. The advantage in mixing a nitrate with gun-cotton is that
it supplies oxygen, and by converting all the carbon into carbonic acid,
prevents the formation of the poisonous gas carbonic oxide (CO). The
nitrates of potassium and barium are also used admixed with nitro-
cellulose in several of the sporting smokeless powders.
~The Manufacture of Tonite.~--The explosive tonite was patented by Messrs
Trench, Faure, and Mackie, and is manufactured at Faversham and Melling at
the works of the Cotton Powder Company, and at San Francisco by the Tonite
Powder Company. It consists of finely divided and macerated gun-cotton
incorporated with finely ground nitrate of barium which has been carefully
recrystallised. It is made by acting upon carbonate of barium[A] with
nitric acid. The wet and perfectly purified, finely pulped gun-cotton is
intimately mixed up between edge runners with about the same weight of
nitrate, and the mixing and grinding continued until the whole has become
an intimately mixed paste. This paste is then compressed into cartridges,
formed with a recess at one end for the purpose of inserting the
detonator. The whole is then covered with paraffined paper.
[Footnote A: Witherite, BaCO_{3} + 2HNO_{3} = Ba(NO_{3})_{2} + CO_{2} +
H_{2}O.]
The tonite No. 2 consisted of gun-cotton, nitrates of potash and soda,
charcoal and sulphur. Tonite No. 3[A] is composed as follows:--Gun-cotton,
19 per cent.; di-nitro-benzol, 13 per cent.; and barium nitrate, 68 per
cent. or similar proportions. It is a yellowish colour, and being slower
in its explosive action, is better adapted for blasting soft rock.
[Footnote A: Tonite No. 1 was patented by Messrs Trench, Faure, and
Mackie, and tonite Nos. 2 and 3 by Trench alone.]
Tonite is extensively used in torpedoes and for submarine blasting, also
for quarries, &c. Large quantities were used in the construction of the
Manchester Ship Canal. Among its advantages are, that the English railways
will take tonite on the same footing as gunpowder; it is a very dense
material; if wetted it can easily be dried in the sun; it very readily
explodes by the use of a proper detonator; while it burns very slowly and
without the least danger; the cartridges being waterproofed, it can be
employed in wet bore holes, and it can be tamped with water; and finally,
as it contains sufficient oxygen to oxidise the carbon, no carbonic oxide
(CO) gas is formed, i.e., its detonation is perfect. It is a very safe
explosive to use, being little susceptible to either blows or friction.
Not long ago, a committee, composed of Prof. P. Bedson, Drs Drummond and
Hume, Mr T. Bell, one of H.M. Inspectors of Coal Mines, and others, in
considering the problem whether the fumes produced by the combustion of
tonite were injurious to health, carried out a series of experiments in
coal mines for this purpose. The air at the "intake" was analysed, also
the air of the "return," and the smoky air in the vicinity of the shot
holes. The cartridge was surrounded by the flame-extinguishing mixture,
and packed in a brown paper bag. During the first experiment nineteen
shots were fired (= 6.29 lbs. tonite). The "return" air showed only a
trace of carbonic oxide gas (CO). At the second experiment thirteen shots
were fired (= 4.40 lbs. tonite), and analysis of the air of the "return"
showed that CO was present in traces only, whilst the fumes contained only
1.9 to 4.8 parts per 10,000.
~Dangers in connection with the Manufacture of Guncotton, &c.~--Of all the
nitro compounds, the least dangerous to manufacture are gun-cotton and
collodion-cotton. The fact that the Stowmarket Factory is within five
minutes' walk of the town shows how safe the manufacture of this explosive
is regarded. With the exception of the nitration and the compression into
blocks or discs, the whole process is worked with a large excess of water,
and the probability of an explosion is thus reduced to a minimum. Among
the precautions that should, however, be taken, are--first, the careful
extraction of the resinous and soluble substances from the cotton before
nitration, as it was shown many years ago by Sir F.A. Abel that the
instability of the gun-cotton first manufactured in England and Austria
was chiefly due to these compounds. They are generally removed by boiling
the cotton in a soda solution.
The actual nitration of cotton is not a dangerous operation, but the
operations of wringing in the hydro-extractors, and washing the nitro-
cotton after it leaves the first centrifugal machine, are somewhat so.
Great care should be taken that the wrung-out nitro-cotton at once comes
in contact with a large excess of water, i.e., is at once immersed
entirely in the water, since at this stage it is especially liable to
decomposition, which, once started, is very difficult to stop. The warmer
the mixture and the less water it contains, the more liable it is to
decomposition; hence it is that on warm and damp days the centrifugal
machines are most likely to fire. The commencement of decomposition may be
at once detected by the evolution of red fumes. Directly the gun-cotton is
immersed in the large quantity of water in the beater and poacher it is
safe.
In order that the final product may be stable and have good keeping
qualities, it is necessary that it should be washed completely free from
acid. The treatment in the beater and poacher, by causing the material to
assume the state of a fine pulp, in contact with a large quantity of
water, does a good deal to get rid of the free acid, but the boiling
process is absolutely necessary. It has been proposed to neutralise the
free acid with a dilute solution of ammonia; and Dr C.O. Weber has
published some experiments bearing upon this treatment. He found that
after treatment with ammonia, pyroxyline assumed a slightly yellowish
tinge, which was a sure sign of alkalinity. It was then removed from the
water, and roughly dried between folds of filter paper, and afterwards
dried in an oven at 70° C. After three hours, however, an explosion took
place, which entirely destroyed the strong copper oven in which the nitro-
cotton (about one oz.) had been drying. The explosion was in some respects
remarkable. The pyroxyline was the di-nitro-cellulose (or possibly the
penta-nitro?), and the temperature was below the igniting point of this
material (40° C. would have been a better temperature). Dr Weber
determined the ignition point of his di-nitro-cellulose, and found it to
be 194° to 198° C., and he is therefore of opinion that the explosion was
due to the treatment of the partially washed material with ammonia. A
certain quantity of ammonium nitrate was probably formed, and subsequently
dried upon the nitro-cellulose, in a state of very fine subdivision. The
faintest trace of acid would then be sufficient to bring about the
explosive ignition of the ammonium nitrate.
The drying of gun-cotton or collodion-cotton is also a somewhat dangerous
operation. A temperature of 40° C. (104° F.) should not be exceeded, and
thermometers should be placed in the nitro-cotton, and the temperature
frequently observed. An electric alarm thermometer is also a useful
adjunct to the cotton drying house. Great care must also be taken that
there are no exposed hot-water pipes or stoves in the drying house, as the
fine gun-cotton dust produced by the turning or moving of the material
upon the shelves would settle upon such pipes or stoves, and becoming hot,
would be very sensitive to the least friction. The floor also should be
covered with linoleum or indiarubber. When hot currents of air are made to
pass over the surface of gun-cotton, the gun-cotton becomes electrified.
It is important, therefore, to provide some means to carry it away. Mr
W.F. Reid, F.I.C., was the first to use metal frames, carriers, and
sieves, upon which is secured the cloth holding the gun-cotton, and to
earth them.
The compression of gun-cotton into blocks, discs, &c., is also attended
with considerable risk. Mr O. Guttmann, in an interesting paper upon "The
Dangers in the Manufacture of Explosives" (_Jour. Soc. Chem. Ind._, No. 3,
vol. xi., 1892), says: "The compression of gun-cotton into cartridges
requires far more care than that of gunpowder, as this is done in a warm
state, and gun-cotton even when cold, is more sensitive than gunpowder.
When coming out of the centrifugal machines, the gun-cotton should always
pass first through a sieve, in order to detect nails or matches which may
by chance have got into it. What has been said as to gunpowder presses
applies still more to those for gun-cotton, although the latter are always
hydraulic presses. Generally the pistons fit the mould perfectly, that is
to say, they make aspiration like the piston of a pump. But there is no
metal as yet known which for any length of time will stand the constant
friction of compression, and after some time the mould will be wider in
that part where the greatest compression takes place. The best metal for
this purpose has proved to be a special steel made by Krupp, but this also
is only relatively better; for pistons I prefer hard cast iron. If the
position of the moulds and pistons is not exactly the same in all cases,
what the Germans call 'Ecken' (English 'binding') will take place, viz.,
the mould will stand obliquely to the piston, and a dangerous friction
will result." "Of course, it is necessary to protect the man working the
hydraulic valves during compression. At Waltham Abbey they have a curtain
made of ship's hawsers, which is at the same time elastic and resistant."
Mr Guttmann has found that a partition wall 12 inches thick, made of
2-inch planks, and filled with ground cinders, gives very effective
protection. A door in this partition enables the workman to get to the
press, and a conical tube penetrates the wall, enabling the man to see the
whole work from a safe standpoint. The roof, or one side of the building,
should be of glass, so as to give the explosion a direction.
~Trench's Fire-extinguishing Compound~ is manufactured by the Cotton
Powder Company at Faversham, and is the invention of Mr George Trench,
F.C.S., the manager of the Company. The object of the invention is to
surround the cartridges of tonite, when used in coal mines, with a fire-
extinguishing compound. If a charge of tonite, dynamite, or gelatine
dynamite is put inside a few ounces of this mixture, and then fired, not
the least trace of flame can be observed, and experiments appear to show
that there is no flame at all. The compound consists of sawdust
impregnated with a mixture of alum and chlorides of sodium and ammonia.
Fig. 22 shows the manner of placing the tonite cartridge in the paper bag,
and surrounding it with the fire-extinguishing compound, _aa_. The
attachment of the fuse and detonator is also shown.
[Illustration: FIG. 22.--TRENCH'S FIRE-EXTINGUISHING CARTRIDGE.]
The following report (taken from the _Faversham News_, 22nd Oct. 1887) of
experiments conducted in the presence of several scientific and mining men
will show its value:--"A large wrought-iron tank, of 45 cubic feet
capacity, had been sunk level with the ground in the middle of the yard;
to this tank the gas had been laid on, for a purpose that will be
explained later on. The charges were fired by means of electricity, a
small dynamo firing machine being placed from 30 to 40 yards away from the
'mine.'" Operations were commenced by the top of the tank being covered
over and plastered down in order to make it air-tight; then a sufficient
quantity of coal gas was placed in it to make it highly inflammable and
explosive, the quantity being ascertained by a meter which had been fixed
specially for the purpose. Whilst the gas was being injected the cartridge
was prepared.
The first experiment was to try whether a small charge of tonite--fired
without the patent extinguisher--would ignite the gas. The gas having been
turned on, a miner's lamp was placed in the "tank," but this was
extinguished before the full quantity of gas had gone through the meter.
However, the gas being in, the charge of 1-1/4 oz. tonite was placed in
the "mine," the detonator was connected by means of long wires to the
dynamo machine, and the word was given to "fire." With a tremendous
report, and a flash of fire, the covering of the mine flew in all
directions, clearly showing that the gas had exploded. The next cartridge
(a similar charge) was prepared with the patent compound. First of all a
brown paper case of about 2 inches diameter was taken, and one of the
tonite cartridges was placed in the centre of it, the intervening space
between the charge and-the case being packed with the "fire-extinguishing
compound." The mine having had another supply of gas injected, the
protected cartridge was placed inside and fired. The result was
astonishing, the explosion not being nearly so loud, whilst there was not
the least flash of fire. "Protected" and "unprotected" charges were fired
at intervals, gas being turned into the tank on each occasion. Charges of
tonite varying from 1 to 6 oz. were also used with the compound. The
report was trifling, whilst no flash could be seen.
~Uses of Collodion-Cotton.~--The collodion or soluble gun-cotton is used
for a variety of purposes. The chief use is, however, for the manufacture
of the various explosive gelatine compounds, of which blasting gelatine is
the type. It is also very extensively used in the manufacture of smokeless
powders, both military and sporting--in fact, very few of them do not
contain it. In some, however, nitro-lignose or nitrated wood is used
instead. This, however, is chemically the same thing, viz., nitro-
cellulose, the cellulose being derived from the wood fibre. It is more
used in this connection than the higher nitrate gun-cotton. Another use to
which it has been applied very extensively, of recent years, is in the
manufacture of "celluloid." It is used in photography for the preparation
of the films on the sensitised plates, and many other purposes. Dissolved
in a solution of two parts ether and one of alcohol, it forms the solution
known as collodion, used for a variety of purposes, such as a varnish, as
a paint for signals; in surgery, for uniting the edges of wounds.
Quite lately, Mr Alfred Nobel, the well-known inventor of dynamite, has
patented the use of nitro-cellulose, hydro- or oxy-cellulose, as an
artificial substitute for indiarubber. For this purpose it is dissolved in
a suitable non-volatile or slightly volatile "solvent," such as nitro-
naphthalene, di-nitro-benzene, nitro-toluene, or its homologues; products
are obtained varying from a gelatinous consistency to the hardness of
ebonite. The proportions will vary from about 20 per cent. of nitro-
cellulose in the finished product, forming a soft rubber, to 50 per cent.
nitrating celluloid, and the "solvent" chosen will depend on the use to
which the rubber substitute is to be put, the liquids giving a more
elastic substance, whilst mixtures of solids and liquids may be employed
when the product is to be used at high temperatures. By means of rollers
steam heated, the incorporation may be accomplished without the aid of a
volatile liquid, or the nitro-cellulose may be employed wet, the water
being removed after "solution."
It is advisable to use the cellulose nitrated only just enough to render
it suitable, in order to reduce the inflammability of the finished
product. Mr W. Allen, M.P., of Gateshead, proposed to use celluloid for
cartridge cases, and thus to lighten ammunition, and prevent jambing, for
the case will be resolved into gases along with the powder. Extractors
will also be done away with.
~Celluloid~ is an intimate mechanical mixture of pyroxyline (gun-cotton or
collodion-cotton) with camphor, first made by Hyatt, of Newark, U.S.A.,
and obtained by adding the pyroxyline to melted camphor, or by strongly
compressing the two substances together, or by dissolving the constituents
in an appropriate solvent, e.g., alcohol or ether, and evaporating to
dryness. A combination of the two latter methods, i.e., partial solution,
with pressure, is now usually adapted. The pyroxyline employed is
generally the tetra- and penta-nitrated cellulose, the hexa-nitrate
(gun-cotton) being but seldom used on account of its explosive properties.
Care is taken to prevent the formation of the hexa-nitrate by immersing
the cellulose in only moderately strong nitric acid, or in a warm mixture
of nitric and sulphuric acids. The paper, either in small pieces or in
sheets, is immersed for about twenty-five minutes in a mixture of 2 parts
of nitric acid and 5 parts of sulphuric acid, at a temperature of about
30° C., after which the nitrated cellulose is thoroughly washed with water
to remove the last traces of free acid, pressed, and whilst still moist,
mixed with the camphor.
In the process of Trebouillet and De Besancele, the cellulose, which may
be in the form of paper, cotton, or linen, is twice nitrated--first in the
acid mixture employed in a previous operation; and secondly, in a fresh
mixture of 3 parts sulphuric acid of 1.83 specific gravity, and 2 parts
concentrated nitric acid containing nitrous acid. After each nitration the
mass is subjected to pressure, and is then carefully washed with water, to
which, at the last, a small quantity of ammonia or caustic soda is added
to remove the final traces of acid. The impregnation of the pyroxyline
with the camphor is effected in a variety of ways.
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° 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° to 40°
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° 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° to 35° C., but would not be true if
the temperature were raised to 50° to 55° 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 formulæ 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 formulæ 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° 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° C. Time of immersion, forty-five minutes.
The 60° 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° | 62° | 31 | ... |
| 2. " | 60° | 62° | 18 | ... |
| 3. Cloudy | 60° | 62° | 7 | ... |
| 4. Rain | 60° | 63° | 0 | 0 |
| 5. Clear | 58° | 62° | 15 | ... |
| 6. Rainy | 58° | 62° | ... | 2 |
| 7. Cloudy | 62° | 65° | ... | 10 |
| 8. Clear | 60° | 62° | 5 | ... |
| 9. Partly Clear| 50° | 60° | ... | 3 |
|10. " | 58° | 60° | ... | 10 |
|11. Cloudy | 58° | 60° | 8 | ... |
|12. Rainy | 58° | 60° | ... | 10 |
|13. Partly CLear| 50° | 58° | 20 | ... |
|14. Cloudy | 50° | 60° | 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° 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 Mühlhäusen 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° 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° to 25° 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.
Dr Mühlhäusen, working on these lines in the laboratory, prepared nitro-
starch which contained 10.96 and 11.09 per cent. of nitrogen. When in the
state of powder it is snow-white in colour; it becomes electrified when
rubbed; it is very stable, and soluble even in the cold in nitro-
glycerine. He has also prepared a tetra-nitro-starch containing 10.58 and
10.50 per cent. of nitrogen, by pouring water into a solution of starch in
nitric acid which had stood for several days. The substance thus produced
in the laboratory had all the properties of that prepared by the other
process.
The production of penta-nitro-starch is effected by adding 20 grms. of
rice-starch--previously dried at a temperature of 100°C., in order to
eliminate all moisture--to a mixture of 100 grms. of nitric acid, specific
gravity 1.501, and 300 grms. of sulphuric acid, specific gravity 1.8 (some
tetra-nitro-starch is also formed at the same time). After standing in
contact with these mixed acids for one hour the starch has undergone a
change, and the mass may now be discharged into a large quantity of water,
and then washed, first with water, and finally with an aqueous solution of
soda. The yield in Dr Mühlhäusen's experiments was 147.5 per cent.
The substance thus formed is now heated with ether-alcohol, the ether is
distilled off, and the penta-nitro-starch appears as a precipitate, whilst
the tetra-nitro-starch, which is formed simultaneously, remains in
solution in the alcohol. As obtained by this process, it contained 12.76
and 12.98 per cent. nitrogen, whilst the soluble tetra-nitro-starch
contained 10.45 per cent.
Hexa-nitro-starch is the product chiefly formed when 40 grms. of dry
starch are treated with 400 grms. of nitric acid, specific gravity 1.501,
and allowed to stand in contact for twenty-four hours; 200 grms. of this
mixture are then poured into 600 c.c. of sulphuric acid of 66° B. The
result of this manipulation is a white precipitate, which contains
13.52-13.23 and 13.22 per cent. nitrogen; and consists, therefore, of a
mixture of penta- and hexa-nitro-starch.
The experiments undertaken with these substances demonstrated that those
prepared by precipitating the nitro-starch with strong sulphuric acid were
less stable in character or properties than those which were precipitated
by water or weak sulphuric acid. Dr Mühlhäusen is of opinion that possibly
in the former case a sulpho-group may be formed, which in small quantity
may occasion this instability.
The following table shows the behaviour of these substances prepared in
different ways and under various conditions:--
__________________________________________________________________
| | |
| | SAMPLES. |
| |____________________________________________|
| | | | | | |
| | A. | B. | C. | D. | E. |
| Ignition-point |175° C. |170° C. |152° C. |121° C. |155° C. |
| Stability |Stable |Stable |Unstable|Unstable|Unstable|
| Per cent. of N. | 11.02 | 10.54 | 12.87 | 12.59 | 13.52 |
| 96 per cent. alcohol| Sol. | Sol. | Insol. | Insol. | Insol. |
| Ether | Insol. | Insol. | Insol. | Insol. | Insol. |
| Ether-alcohol | Sol. | Sol. | Sol. | Sol. | Sol. |
| Acetic Ether | Sol. | Sol. | Sol. | Sol. | Sol. |
|_____________________|________|________|________|________|________|
These samples were prepared as follows:--
A. From 1 part nitric acid and 2 parts sulphuric acid (containing 70 per
cent. H_{2}O).
B. From 1 part nitric acid and water.
C. From 1 part nitric and 3 parts H_{2}SO_{4} (con.).
D. From 1 part nitric and 3.5 parts con. H_{2}SO_{4}.
E. From 1 part nitric and 3 parts con. H_{2}SO_{4}.
Dr Mühlhäusen is of opinion that these compounds may be turned to
practical account in the production of good smokeless powder. He
recommends the following proportions and method. Six grms. of nitro-jute
and 2 grms. of nitro-starch are mixed together, and moistened with acetic
ether. These ingredients are then worked together into a uniform mass, and
dried at a temperature ranging between the limits 50° to 60° C. He has
himself prepared such a smokeless powder, which proved to contain 11.54
per cent. of nitrogen, and was very stable. Further details of Dr
Mühlhäusen's work upon nitro-starch can be found in _Dingler's
Polytechnisches Journal_, paper "Die höhren Salpetersäureäther der
Stärke," 1892, Band 284, s. 137-143, and a Bibliography up to 1892 in
_Arms and Explosives_, December 1892.
M. Berthelot gives the heat of formation of nitro-starch as 812 cals. for
1 grm., and the heat of total combustion as equal to 706.5 cals. for 207
grms., or for 1 grm. 3,413 cals. The heat of decomposition could only be
calculated if the products of decomposition were given, but they have not
as yet been studied, and the quantity of oxygen contained in the compound
is far from being sufficient for its complete combustion. Berthelot and
Vieille found the average velocities for nitro-starch powder, density of
charge about 1.2, in a tin tube 4 mm. external diameter, to be, in two
experiments, 5,222 m. and 5,674 m. In a tin tube 5.5 mm. external
diameter, the velocity was 5,815 m., and in lead tube 5,006 m. (density
1.1 to 1.2). The starch powder is hygroscopic, and is insoluble in water
and alcohol. When dry it is very explosive, and takes fire at about 350°
F. Mr Alfred Nobel has taken out a patent (Eng. Pat. No. 6,560, 88) for
the use of nitro-starch. His invention relates to the treatment of nitro-
starch and nitro-dextrine, for the purpose of producing an explosive
powder, to be used in place of gunpowder. He incorporates these materials
with nitro-cellulose, and dissolves the whole in acetone, which is
afterwards distilled off. A perfect incorporation of the ingredients is
thus brought about.
~Nitro-Jute.~--It is obtained by treating jute with nitric acid. Its
properties have been studied by Messrs Cross and Bevan (_Jour. Chem.
Soc._, 1889, 199), and by Mühlhäusen. The latter used for its nitration an
acid mixture composed of equal parts of nitric and sulphuric acids, which
was allowed to act upon the jute for some time. He found that with long
exposure, i.e., from three to four hours in the acids, there was a
disintegrating of the fibre-bundles, and the nitration was attended by
secondary decomposition and conversion into products soluble in the acid
mixture. Cross and Bevan's work upon this subject leads them to conclude
that the highest yield of nitrate is represented by an increase of weight
of 51 per cent. They give jute the empirical formula C_{12}H_{18}O_{9} (C
= 47 per cent. H = 6 per cent., and O = 47 per cent.), and believe its
conversion into a nitro compound to take place thus:--
C_{12}H_{18}O + 3HNO_{3} = C_{12}H_{15}O_{6}(NO_{3})_{3} + 3H_{2}O.
This is equivalent to a gain in weight of 44 per cent. for the tri-
nitrate, and of 58 per cent. for the tetra-nitrate. The formation of the
tetra-nitrate appears to be the limit of nitration of jute-fibre. In other
words, if we represent the ligno-cellulose molecule by a C_{12} formula,
it will contain four hydroxyl (OH) groups, or two less than cellulose
similarly represented. The following are their nitration results:--
Acids used.--I. HNO_{3} sp. gr. 1.43, and H_{2}SO_{4} = 1.84 equal parts.
II. 1 vol. HNO_{3}(1.5), 1 vol. H_{2}SO_{4}(1.84).
III. 1 vol. HNO_{3}(1.5), 75 vols. H_{2}SO_{4}(1.84).
I. = 144.4; II. = 153.3; III. = 154.4 grms.; 100 grms. of fibre being used
in all three cases.
Duration of exposure, thirty minutes at 18° C.
The nitrogen was determined in the products, and equalled 10.5 per cent.
Theory for C_{12}H_{15}O_{6}(NO_{3})_{3} = 9.5 per cent. and for
C_{12}H_{15}O_{6}(NO_{3})_{4} = 11.5 per cent. These nitrates resemble
those of cellulose, and are in all essential points nitrates of ligno-
cellulose.
Mühlhäusen obtained a much lower yield, and probably, as pointed out by
Cross and Bevan, a secondary decomposition took place, and his products,
therefore, probably approximate to the derivatives of cellulose rather
than to those of ligno-cellulose, the more oxidisable, non-cellulose, or
lignone constituents having been decomposed. In fact, he regards his
product as cellulose penta-nitrate (C_{12}H_{16}O_{5}(ONO_{2})_{5}). The
_Chemiker Zeitung_, xxi., p. 163, contains a further paper by Mühlhäusen
on the explosive nitro-jute. After purifying the jute-fibre by boiling it
with a 1 per cent. solution of sodium carbonate, and washing with water,
he treated 1 part of the purified jute with 15 parts of nitro-sulphuric
acid, and obtained the following results with different proportions of
nitric to sulphuric acids:--
Yield Ignition Nitrogen.
per cent. Point.
Experiment I.-- 1. HNO_{3} 1. H_{2}SO_{4} 129.5 170° C. 11.96%
" II. " 2. " 132.2 167° C. 12.15%
" III. " 3. " 135.8 169° C. 11.91%
An experiment made with fine carded jute and the same mixture of acids as
in No. II. gave 145.4 per cent. nitro-jute, which ignited at 192° C., and
contained 12 per cent. nitrogen. This explosive is not at present
manufactured upon the large scale, and Messrs Cross and Bevan are of
opinion that there is no very obvious advantage in the use of lignified
textile fibre as raw materials for explosive nitrates, seeing that a large
number of raw materials containing cellulose (chiefly as cotton) can be
obtained at a cheaper rate, and yield also 150 to 170 per cent. of
explosive material when nitrated, and are in many ways superior to the
products obtained hitherto from jute.
~Nitro-mannite~ is formed by the action of nitric acid on mannite, a
hex-acid alcohol closely related to sugar. It occurs abundantly in manna,
which is the partly dried sap of the manna-ash (_Fraxinus ornus_). It is
formed in the lactic acid fermentation of sugar, and by the action of
nascent hydrogen on glucose and cellulose, or on invert sugar. Its formula
is C_{6}H_{8}(OH)_{6} and that of nitro-mannite C_{6}H_{8}(NO_{3})_{6}.
Mannite crystallises in needles or rhombic prisms, which are soluble in
water and alcohol, and have a sweet taste. Nitro-mannite forms white
needle-shaped crystals, insoluble in water, but soluble in ether or
alcohol. When rapidly heated, they ignite at about 374° F., and explode at
about 590° F. It is more susceptible to friction and percussion than
nitro-glycerine, and unless pure it is liable to spontaneous
decomposition. It is considered as the nitric ether of the hexatomic
alcohol mannite. It is formed by the action of a mixture of nitric and
sulphuric acids upon mannite--
C_{6}H_{8}(OH)_{6} + 6HNO_{3} = C_{6}H_{8}(NO_{3})_{6} + 6H_{2}O.
Its products of explosion are as shown in the following equation:--
C_{6}H_{8}(OH)_{6} = 6CO_{2} + 4H_{2}O + 3N_{2} + O_{2}.
Its percentage composition is as follows:--Carbon, 15.9 per cent.;
hydrogen, 1.8 per cent.; nitrogen, 18.6 per cent.; and oxygen, 63.7 per
cent. Its melting point is 112 to 113° C., and it solidifies at 93°. When
carefully prepared and purified by recrystallisation from alcohol, and
kept protected from sunlight, it can be kept for several years without
alteration.
Nitro-mannite is more dangerous than nitro-glycerine, as it is more
sensitive to shock. It is intermediate in its shattering properties
between nitro-glycerine and fulminate of mercury. It explodes by the shock
of copper on iron or copper, and even of porcelain on porcelain, provided
the latter shock be violent. Its heat of formation from its elements is
+156.1 calories. It is not manufactured upon the commercial scale.
Besides the nitro compounds already described, there are many others, but
they are of little importance, and are none of them made upon the large
scale. Among such substances are _nitro-coal_, which is made by the action
of nitric acid on coal; _nitro-colle_, a product which results from the
action of nitric acid on isinglass or gelatine, soaked in water. It is
then treated with the usual acids.
Another method is to place strong glue in cold water until it has absorbed
the maximum amount of the latter. The mixture is solidified by the
addition of nitric acid, nitrated in the usual way, and well washed.
Abel's _Glyoxiline_ is only nitrated gun-cotton impregnated with nitro-
glycerine. Nitro-lignine is only nitro-cellulose made from wood instead of
cotton; and nitro-straw is also only nitro-cellulose. The explosive known
as _Keil's Explosive_ contains nitro-glucose. Nitro-molasses, which is a
liquid product, has also been proposed, and nitro-saccharose, the product
obtained by the nitration of sugar. It is a white, sandy, explosive
substance, soluble in alcohol and ether. When made from cane sugar, it
does not crystallise; but if made from milk sugar, it does. It has been
used in percussion caps, being stronger and quicker than nitro-glycerine.
It is, however, very sensitive and very hygroscopic, and very prone to
decomposition. Nitro-tar, made from crude tar-oil, by nitration with
nitric acid of a specific gravity of 1.53 to 1.54. Nitro-toluol is used,
mixed with nitro-glycerine. This list, however, does not exhaust the
various substances that have been nitrated and proposed as explosives.
Even such unlikely substances as horse dung have been experimented with.
None of them are very much used, and very few of them are made upon the
manufacturing scale.