_MANUFACTURE OF NITRO-GLYCERINE._
Properties of Nitro-Glycerine--Manufacture of Nitro-Glycerine--Nitration--
The Nathan Nitrator--Separation--Filtering and Washing--The Waste Acids--
Treatment of the Waste Acid from the Manufacture of Nitro-Glycerine and
Gun-Cotton.
~Properties of Nitro-Glycerine.~--Nitro-glycerol is a heavy oily liquid of
specific gravity 1.6 at 15° C., and when quite pure is colourless. The
commercial product is a pale straw yellow, but varies much according to
the purity of the materials used in its manufacture. It is insoluble in
water, crystallises at 10.5° C., but different commercial samples behave
very differently in this respect, and minute impurities prevent or delay
crystallisation. Solid nitro-glycerol[A] melts at about 12° C., but
requires to be exposed to this temperature for some time before melting.
The specific gravity of the solid form is 1.735 at +10° C.; it contracts
one-twelfth of its volume in solidifying. Beckerheim[B] gives the specific
heat as 0.4248 between the temperatures of 9.5° and 9.8° C., and L. de
Bruyn gives the boiling point as above 200°.
[Footnote A: Di-nitro-mono chlorhydrin, when added to nitro-glycerine up
to 20 per cent., is said to prevent its freezing.]
[Footnote B: _Isb., Chem. Tech._, 22, 481-487. 1876.]
Nitro-glycerine has a sweet taste, and causes great depression and
vertigo. It is soluble in ether, chloroform, benzene, glacial acetic acid,
and nitro-benzene, in 1.75 part of methylated spirit, very nearly
insoluble in water, and practically insoluble in carbon bisulphide. Its
formula is C_{3}H_{5}(NO_{3})_{3}, and molecular weight 227. When pure, it
may be kept any length of time without decomposition. Berthelot kept a
sample for ten years, and Mr G. M'Roberts, of the Ardeer Factory, for nine
years, without their showing signs of decomposition; but if it should
contain the smallest trace of free acid, decomposition is certain to be
started before long. This will generally show itself by the formation of
little green spots in the gelatine compounds, or a green ring upon the
surface of liquid nitro-glycerine. Sunlight will often cause it to
explode; in fact, a bucket containing some water that had been used to
wash nitro-glycerine, and had been left standing in the sun, has in our
experience been known to explode with considerable force. Nitro-glycerine
when pure is quite stable at ordinary temperatures, and samples have been
kept for years without any trace of decomposition. It is very susceptible
to heat, and even when quite pure will not stand a temperature of 100° C.
for a longer period than a few hours, without undergoing decomposition. Up
to a temperature of 45° C., however, properly made and purified nitro-
glycerine will remain unchanged almost indefinitely. The percentage
composition of nitroglycerine is as follows:--
Found. Theory for C_{3}H_{5}(N0_{2})_{3}.
Carbon 15.62 15.86 per cent.
Hydrogen 2.40 2.20 "
Nitrogen 17.90 18.50 "
Oxygen ... 63.44 "
The above analysis is by Beckerheim. Sauer and Adou give the nitrogen as
18.35 to 10.54 per cent. by Dumas' method; but I have never found any
difficulty in obtaining percentages as high as 18.46 by the use of Lunge's
nitrometer. The decomposition products by explosion are shown by the
following equation--
2C_{3}H_{5}(NO_{3})_{3} = 6CO_{2} + 5H_{2}O + 6N + O;
that is, it contains an excess of 3.52 per cent. of oxygen above that
required for complete combustion; 100 grms. would be converted into--
Carbonic Acid (CO_{2}) 58.15 per cent.
Water 19.83 "
Oxygen 3.52 per cent.
Nitrogen 18.50 "
The volume of gases produced at 0° and 760 mm., calculated from the above,
is 714 litres per kilo, the water being taken as gaseous. Nitro-glycerine
is decomposed differently if it is ignited as dynamite (i.e., kieselguhr
dynamite), and if the gases are allowed to escape freely under a pressure
nearly equal to that of the atmosphere. Sarrau and Vieille obtained under
these conditions, for 100 volumes of gas--
NO 48.2 per cent.
CO 35.9 "
CO_{2} 12.7 "
H 1.6 per cent.
N 1.3 "
CH_{4} 0.3 "
These conditions are similar to those under which a mining charge, simply
ignited by the cap, burns away slowly under a low pressure (i.e., a miss
fire). In a recent communication, P.F. Chalon (_Engineering and Mining
Journal_, 1892) says, that in practice nitro-glycerine vapour, carbon
monoxide, and nitrous oxide, are also produced as the result of
detonation, but he attributes their formation to the use of a too feeble
detonator.
Nitro-glycerine explodes very violently by concussion. It may be burned in
an open vessel, but if heated above 250° C. it explodes. Professor C.E.
Munroe gives the firing point as 2O3°-2O5° C., and L. de Bruyn[A] states
its boiling point as 185°. He used the apparatus devised by Horsley. The
heat of formation of nitro-glycerine, as deduced from the heat of
combustion by M. Longuinine, is 432 calories for 1 grm.; and the heat of
combustion equals 1,576 cals. for 1 grm. In the case of nitro-glycerine
the heat of total combustion and the heat of complete decomposition are
interchangeable terms, since it contains an excess of oxygen. According to
Dr W.H. Perkin, F.R.S.,[B] the magnetic rotation of nitro-gylcerine is
5,407, and that of tri-methylene nitrate, 4.769 (diff. = .638). Dr Perkin
says: "Had nitro-glycerine contained its nitrogen in any other combination
with oxygen than as -O-NO_{2}, as it might if its constitution had been
represented as C_{3}H_{2}(NO_{2})_{3}(OH)_{3}, the rotation when compared
with propyl nitrate (4.085) would be abnormal."
[Footnote A: _Jour. Soc. Chem. Ind._, June 1896, p. 471.]
[Footnote B: _Jour. Chem. Soc._, W.H. Perkin, 1889, p. 726.]
The solubility of nitro-glycerine in various solvents has been
investigated by A.H. Elliot; his results may be summarised as follows:--
_______________________________________________________________________
| |
Solvent. | Cold. | Warm.
_____________________________|______________________|__________________
| |
Water | Insoluble | Slightly soluble
Alcohol, absolute | Soluble | Soluble
" 93% | " | "
" 80% | Slowly soluble | "
" 50% | Insoluble | Slightly soluble
Methyl alcohol | Soluble | Soluble
Amyl " | " | "
Ether, ethylic | " | "
" acetic | " | "
Chloroform | " | "
Acetone | " | "
Sulphuric acid (1.845) | " | "
Nitric acid (1.400) | Slowly soluble | "
Hydrochloric acid (1.200) | Insoluble, decomposed| Slowly soluble
Acetic acid, glacial | Soluble | Soluble
Carbolic acid | " | "
Astral oil | Insoluble | Insoluble
Olive " | Soluble | Soluble
Stearine oil | " | "
Mineral jelly | Insoluble | Insoluble
Glycerine | " | "
Benzene | Soluble | Soluble
Nitro-benzene | " | "
Toluene | " | "
Carbon bi-sulphide | Insoluble | Slightly affected
Turpentine | " | Soluble
Petroleum naphtha, 71°-76° B.| " | Insoluble
Caustic soda (1:10 solution) | Insoluble. | Insoluble.
Borax, 5% solution | " | "
Ammonia (.980) | " | " slightly
| | affected.
Ammonium sulph-hydrate | Insoluble, sulphur | Decomposed.
| separates |
Iron sulphate solution | Slightly affected | Affected.
Iron chloride (1.4 grm. Fe | Slowly affected | Decomposed.
to 10 c.c. N_{2}O) | |
Tin chloride | Slightly affected | Affected.
_____________________________|______________________|__________________
Many attempts have been made to prepare nitro-glycerine explosives capable
of withstanding comparatively low temperatures without freezing, but no
satisfactory solution of the problem has been found. Among the substances
that have been proposed and used with more or less success, are nitro-
benzene, nitro-toluene, di-nitro-mono-chlorhydrine, solid nitro
derivatives of toluene,[A] are stated to lower the freezing point of
nitro-glycerine to -20°C. without altering its sensitiveness and
stability. The subject has been investigated by S. Nauckhoff,[B] who
states that nitroglycerine can be cooled to temperatures (-40° to -50° C.)
much below its true freezing point, without solidifying, by the addition
of various substances. When cooled by means of a mixture of solid carbon,
dioxide, and ether, it sets to a glassy mass, without any perceptible
crystallisation. The mass when warmed to 0°C. first rapidly liquefies and
then begins to crystallise. The true freezing point of pure nitro-
glycerine was found to be 12.3°C. The technical product, owing to the
presence of di-nitro-glycerine, freezes at 10.5° C. According to Raoult's
law, the lowering of the freezing point caused by _m_ grms. of a substance
with the molecular weight M, when dissolved in 100 grms. of the solvent,
is expressed by the formula: [Delta] = E(_m_/M), where E is a constant
characteristic for the solvent in question. The value of E for nitro-
glycerine was found to be 70.5 when calculated, according to Van't Hoff's
formula, from the melting point and the latent heat of fusion of the
substance. Determinations of the lowering of the freezing point of nitro-
glycerine by additions of benzene, nitro-benzene, di-nitro-benzene, tri-
nitro-benzene, p.-nitro-toluene, o.-nitro-toluene, di-nitro-toluene,
naphthalene, nitro-naphthalene, di-nitro-naphthalene, ethyl acetate, ethyl
nitrate, and methyl alcohol, gave results agreeing fairly well with
Raoult's formula, except in the case of methyl alcohol, for which the
calculated lowering of the freezing point was greater than that observed,
probably owing to the formation of complex molecules in the solution. The
results show that, in general, the capacity of a substance to lower the
freezing point of nitro-glycerine depends, not upon its freezing point, or
its chemical composition or constitution, but upon its molecular weight.
Nauckhoff states that a suitable substance for dissolving in nitro-
glycerine, in order to lower the freezing point of the latter, must have a
relatively low molecular weight, must not appreciably diminish the
explosive power and stability of the explosive, and must not be easily
volatile at relatively high atmospheric temperatures; it should, if
possible, be a solvent of nitro-cellulose, and in every case must not have
a prejudicial influence on the gelatinisation of the nitro-cellulose.
[Footnote A: Eng. Pat. 25,797, November 1904.]
[Footnote B: _Z. Angew. Chem._, 1905, 18, 11-22, 53-60.]
~Manufacture of Nitro-Glycerine.~--Nitro-glycerine is prepared upon the
manufacturing scale by gradually adding glycerine to a mixture of nitric
and sulphuric acids of great strength. The mixed acids are contained in a
lead vessel, which is kept cool by a stream of water continually passing
through worms in the interior of the nitrating vessel, and the glycerine
is gradually added in the form of a fine stream from above. The
manufacture can be divided into three distinct operations, viz.,
nitration, separation, and washing, and it will be well to describe these
operations in the above order.
~Nitration.~--The most essential condition of nitrating is the correct
composition and strength of the mixed acids. The best proportions have
been found to be three parts by weight of nitric acid of a specific
gravity 1.525 to 1.530, and containing as small a portion of the oxides of
nitrogen as possible, to five parts by weight of sulphuric acid of a
specific gravity of 1.840 at 15° C., and about 97 per cent. of mono-
hydrate. It is of the very greatest importance that the nitric acid should
be as strong as possible. Nothing under a gravity of 1.52 should ever be
used even to mix with stronger acid, and the nitration will be
proportional to the strength of the acid used, provided the sulphuric acid
is also strong enough. It is also of great importance that the oxides of
nitrogen should be low, and that they should be kept down to as low as 1
per cent., or even lower. It is also very desirable that the nitric acid
should contain as little chlorine as possible. The following is the
analysis of a sample of nitric acid, which gave very good results upon the
commercial scale:--Specific gravity, 1.525, N_{2}O_{4}, 1.03 per cent.;
nitric acid (HNO_{3}), 95.58 per cent.
The amount of real nitric acid (mono-hydrate) and the amount of nitric
peroxide present in any sample should always be determined before it is
used for nitrating purposes. The specific gravity is not a sufficient
guide to the strength of the acid, as an acid having a high gravity, due
to some 3 or 4 per cent of nitric oxides in solution, will give very poor
nitration results. A tenth normal solution of sodium hydroxide (NaOH),
with phenol-phthalein as indicator, will be found the most convenient
method of determining the total acid present. The following method will be
found to be very rapid and reliable:--Weigh a 100 c.c. flask, containing a
few cubic centimetres of distilled water, and then add from a pipette 1
c.c. of the nitric acid to be examined, and reweigh (this gives the weight
of acid taken). Now make up to 100 c.c. at 15° C.; shake well, and take
out 10 c.c. with a pipette; drain into a small Erlenmeyer flask, and add a
little of the phenol-phthalein solution, and titrate with the tenth normal
soda solution.
The nitric peroxide can be determined with a solution of potassium
permanganate of N/10 strength, thus: Take a small conical flask,
containing about 10 c.c. of water, and add from a burette 10 to 16 c.c. of
the permanganate solution; then add 2 c.c. of the acid to be tested, and
shake gently, and continue to add permanganate solution as long as it is
decolourised, and until a faint pink colour is permanent.
_Example._ N/10 permanganate 3.16 grms. per litre, 1 c.c. = O.0046 grm.
N_{2}O_{4}, 2 c.c. of sample of acid specific gravity 1.52 = 3.04 grms.
taken for analysis. Took 20 c.c. permanganate solution, O.0046 x 20 =.092
grm. N_{2}O_{4}, and (.092 x 100)/3.04 = 3.02 per cent. N_{2}O_{4}. The
specific gravity should be taken with an hydrometer that gives the
specific gravity directly, or, if preferred, the 2 c.c. of acid may be
weighed.
A very good method of rapidly determining the strength of the sulphuric
acid is as follows:--Weigh out in a small weighing bottle, as nearly as
possible, 2.45 grms. This is best done by running in 1.33 c.c. of the acid
(1.33 x 1.84 = 2.447). Wash into a large Erlenmeyer flask, carefully
washing out the bottle, and also the stopper, &c. Add a drop of phenol-
phthalein solution and titrate, with a half normal solution of sodium
hydrate (use a 100 c.c. burette). Then if 2.45 grms. exactly have been
taken, the readings on the burette will equal percentages of H_{2}SO_{4}
(mono-hydrate) if not, calculate thus:--2.444 grms. weighed, required 95.4
c.c. NaOH. Then--
2.444 : 95.4 :: 2.45 : _x_ = 95.64 per cent. H_{2}SO_{4}.
It has been proposed to free nitric acid from the oxides of nitrogen by
blowing compressed air through it, and thus driving the gases in solution
out. The acid was contained in a closed lead tank, from which the escaping
fumes were conducted into the chimney shaft, and on the bottom of which
was a lead pipe, bent in the form of a circle, and pierced with holes,
through which the compressed air was made to pass; but the process was not
found to be of a very satisfactory nature, and it is certainly better not
to allow the formation of these compounds in the manufacture of the acid
in the first instance. Another plan, however, is to heat the acid gently,
and thus drive out the nitrous gases. Both processes involve loss of
nitric acid.
Having obtained nitric and sulphuric acids as pure as possible, the next
operation is to mix them. This is best done by weighing the carboys in
which the acids are generally stored before the acids are drawn off into
them from the condensers, and keeping their weights constantly attached to
them by means of a label. It is then a simple matter to weigh off as many
carboys of acid as may be required for any number of mixings, and subtract
the weights of the carboys. The two acids should, after being weighed, be
poured into a tank and mixed, and subsequently allowed to flow into an
acid egg or montjus, to be afterwards forced up to the nitrating house in
the danger area. The montjus or acid egg is a strong cast-iron tank, of
either an egg shape, or a cylinder with a round end. If of the former
shape, it would lie on its side, and upon the surface of the ground, and
would have a manhole at one end, upon which a lid would be strongly bolted
down; but if of the latter shape, the lid, of course, is upon the top, and
the montjus itself is let into the ground. In either case, the principle
is the same. One pipe, made of stout lead, goes to the bottom, and another
just inside to convey the compressed air, the acids flowing away as the
pressure is put on, just as blowing down one tube of an ordinary wash-
bottle forces the water up the other tube to the jet. The pressure
necessarily will, of course, vary immensely, and will depend upon the
height to which the acid has to be raised and the distance to be
traversed.
The mixed acids having been forced up to the danger area, and to a level
higher than the position of the nitrating house, should, before being
used, be allowed to cool, and leaden tanks of sufficient capacity to hold
at least enough acid for four or five nitrations should be placed in a
wooden house upon a level at least 6 or 7 feet above the nitrating house.
In this house also should be a smaller lead tank, holding, when filled to
a certain mark, just enough of the mixed acids for one nitration. The
object of this tank is, that as soon as the man in charge knows that the
last nitration is finished, he refills this smaller tank (which contains
just enough of the mixed acids), and allows its contents to flow down into
the nitrating house and into the nitrator, ready for the next nitration.
The nitration is usually conducted in a vessel constructed of lead, some 4
feet wide at the bottom, and rather less at the top, and about 4 feet or
so high. The size, of course, depends upon the volume of the charge it is
intended to nitrate at one operation, but it is always better that the
tank should be only two-thirds full. A good charge is 16 cwt. of the mixed
acids, in the proportion of three to five; that is, 6 cwt. of nitric acid,
and 10 cwt. of sulphuric acid, and 247 lbs. of glycerine.
Upon reference to the equation showing the formation of nitro-glycerine,
it will be seen that for every 1 lb. of glycerine 2.47 lbs. of nitro-
glycerine should be furnished,[A] but in practice the yield is only a
little over 2 lbs., the loss being accounted for by the unavoidable
formation of some of the lower nitrate of glycerine (the mono-nitrate),
which afterward dissolves in the washing waters. The lead tank (Fig. 5) is
generally cased in woodwork, with a platform in front for the man in
charge of the nitrating to stand upon, and whence to work the various
taps. The top of the tank is closed in with a dome of lead, in which is a
small glass window, through which the progress of the nitrating operation
can be watched. From the top of this dome is a tube of lead which is
carried up through the roof of the building. It serves as a chimney to
carry off the acid fumes which are given off during the nitration. The
interior of this tank contains at least three concentric spirals of at
least 1-inch lead pipe, through which water can be made to flow during the
_whole_ operation of nitrating. Another lead pipe is carried through the
dome of the tank, as far as the bottom, where it is bent round in the form
of a circle. Through this pipe, which is pierced with small holes, about 1
inch apart, compressed air is forced at a pressure of about 60 lbs. in
order to keep the liquids in a state of constant agitation during the
whole period of nitration. There must also be a rather wide pipe, of say 2
inches internal diameter, carried through the dome of the tank, which will
serve to carry the mixed acid to be used in the operation into the tank.
There is still another pipe to go through the dome, viz., one to carry the
glycerine into the tank. This need not be a large bore pipe, as the
glycerine is generally added to the mixed acids in a thin stream (an
injector is often used).
[Footnote A: Thus if 92 lbs. glycerine give 227 lbs. nitro-glycerine,
(277 x 1)/92 = 2.47 lbs.]
[Illustration: FIG. 5.--TOP OF NITRATOR. _A_, Fume Pipe; _B_, Water Pipes
for Cooling; _C_, Acid Mixture Pipe; _E_, Compressed Air; _G_, Glycerine
Pipe and Funnel; _T_, Thermometer; _W_, Window.]
Before the apparatus is ready for use, it requires to have two
thermometers fixed, one long one to reach to the bottom of the tank, and
one short one just long enough to dip under the surface of the acids. When
the tank contains its charge, the former gives the temperature of the
bottom, and the latter of the top of the mixture. The glycerine should be
contained in a small cistern, fixed in some convenient spot upon the wall
of the nitrating house, and should have a pipe let in flush with the
bottom, and going through the dome of the nitrating apparatus. It must of
course be provided with a tap or stop-cock, which should be placed just
above the point where the pipe goes through the lead dome.
Some method of measuring the quantity of glycerine used must be adopted. A
gauge-tube graduated in inches is a very good plan, but it is essential
that the graduations should be clearly visible to the operator upon the
platform in front of the apparatus. A large tap made of earthenware (and
covered with lead) is fixed in the side of the nitrating tank just above
the bottom, to run off the charge after nitration. This should be so
arranged that the charge may be at option run down the conduit to the next
house or discharged into a drowning tank, which may sometimes be necessary
in cases of decomposition. The drowning tank is generally some 3 or 4
yards long and several feet deep, lined with cement, and placed close
outside the building.
The apparatus having received a charge of mixed acids, the water is
started running through the pipes coiled inside the tank, and a slight
pressure of compressed air is turned on,[A] to mix the acids up well
before starting. The nitration should not be commenced until the two
thermometers register a temperature of 18° C. The glycerine tap is then
partially opened, and the glycerine slowly admitted, and the compressed
air turned on full, until the contents of the apparatus are in a state of
very brisk agitation. A pressure of about 40 lbs. is about the minimum (if
247 lbs. of glycerine and 16 cwt. of acids are in the tank). If the
glycerine tube is fitted with an injector, it may be turned on almost at
once. The nitration will take about thirty minutes to complete, but the
compressed air and water should be kept on for an additional ten minutes
after this, to give time for all the glycerine to nitrate. The temperature
should be kept as low as possible (not above 18° C.).
[Footnote A: At the Halton Factory, Germany, cylinders of compressed
carbon dioxide are connected with the air pipes so that in the event of a
failure of the air supply the stirring can be continued with this gas if
necessary.]
The chief points to attend to during the progress of the nitration are--
1. The temperature registered by the two thermometers.
2. The colour of the nitrous fumes given off (as seen through the little
window in the dome of the apparatus).
3. The pressure of the compressed air as seen from a gauge fixed upon the
air pipe just before it enters the apparatus.
4. The gauge showing the quantity of glycerine used. The temperature, as
shown by either of the two thermometers, should not be at any time higher
than 25° C.
If it rises much above this point, the glycerine should be at once shut
off, and the pressure of air increased for some few minutes until the
temperature falls, and no more red fumes are given off.
The nitration being finished, the large earthenware tap at the bottom of
the tank is opened, and the charge allowed to flow away down the conduit
to the next building, i.e., to the separator.
The nitrating house is best built of wood, and should have a close-boarded
floor, which should be kept scrupulously clean, and free from grit and
sand. A wooden pail and a sponge should be kept in the house in order that
the workman may at once clean up any mess that may be made, and a small
broom should be handy, in order that any sand, &c., may be at once
removed. It is a good plan for the nitrator to keep a book in which he
records the time of starting each nitration, the temperature at starting
and at the finish, the time occupied, and the date and number of the
charge, as this enables the foreman of the danger area at any time to see
how many charges have been nitrated, and gives him other useful
information conducive to safe working. Edward Liebert has devised an
improvement in the treatment of nitro-glycerine. He adds ammonium sulphate
or ammonium nitrate to the mixed acids during the operation of nitrating,
which he claims destroys the nitrous acid formed according to the
equation--
(NH_{4})_{2}SO_{4} + 2HNO_{3} = H_{2}SO_{4} + 2N_{2} + 4H_{2}O.
I am not aware that this modification of the process of nitration is in
use at the present time.
The newly made charge of nitro-glycerine, upon leaving the nitrating
house, flows away down the conduit, either made of rubber pipes, or better
still, of woodwork, lined with lead and covered with lids made of wood (in
short lengths), in order that by lifting them at any point the condition
of the conduit can be examined, as this is of the greatest importance, and
the conduit requires to be frequently washed out and the sulphate of lead
removed. This sulphate always contains nitro-glycerine, and should
therefore be burnt in some spot far removed from any danger building or
magazine, as it frequently explodes with considerable violence.
[Illustration: FIG. 6.--SMALL NITRATOR. _N_, Tap for Discharging; _P_,
Water Pipes; _T_, Thermometer; _W_, Windows; _P'_, Glycerine Pipe.]
In works where the manufacture of nitro-glycerine is of secondary
importance, and some explosive containing only perhaps 10 per cent. of
nitroglycerine is manufactured, and where 50 or 100 lbs. of glycerine are
nitrated at one time, a very much smaller nitrating apparatus than the one
that has been already described will be probably all that is required. In
this case the form of apparatus shown in Fig. 6 will be found very
satisfactory. It should be made of stout lead (all lead used for tanks,
&c., must be "chemical lead"), and may be made to hold 50 or 100 lbs. as
found most convenient. This nitrator can very well be placed in the same
house as the separator; in fact, where such a small quantity of nitro-
glycerine is required, the whole series of operations, nitrating,
separation, and washing, &c., may very well be performed in the same
building. It will of course be necessary to place the nitrator on a higher
level than the separator, but this can easily be done by having platforms
of different heights, the nitration being performed upon the highest. The
construction of this nitrator is essentially the same as in the larger
one, the shape only being somewhat different. Two water coils will
probably be enough, and one thermometer. It will not be necessary to cover
this form in with woodwork.
~The Nathan Nitrator.~[A]--This nitrator is the patent of Lt. Col. F.L.
Nathan and Messrs J.M. Thomson and W. Rintoul of Waltham Abbey, and will
probably before long entirely supersede all the other forms of nitrator on
account of its efficiency and economy of working. With this nitrator it is
possible to obtain from 2.21 to 2.22 parts of nitro-glycerine from every 1
part of glycerine. The apparatus is so arranged that the nitration of the
glycerine, the separation of nitro-glycerine produced, as well as the
operation of "after-separation," are carried out in one vessel. The usual
nitrating vessel is provided with an acid inlet pipe at the bottom, and a
glass separation cylinder with a lateral exit or overflow pipe at the top.
This cylinder is covered by a glass hood or bell jar during nitration to
direct the escaping air and fumes into a fume pipe where the flow of the
latter may be assisted by an air injector. The lateral pipe in the
separation cylinder is in connection with a funnel leading to the prewash
tank. The drawing (Fig. 7) shows a vertical section of the apparatus; _a_
is the nitrating vessel of usual construction, having at the bottom an
acid inlet pipe with three branches, one leading to the de-nitrating
plant, _c_ leading to the drowning tank, and _d_, which extends upwards
and has two branches, _e_ leading to the nitrating acids tank, and _f_ to
the waste acid tank. On the sloped bottom of the nitrating vessel _a_ lies
a coil _g_ of perforated pipe for blowing air, and there are in the vessel
several coils _h_, three shown in the drawing, for circulation of cooling
water. At the top of the vessel there is a glass cylinder _i_, having a
lateral outlet _j_ directed into the funnel mouth of a pipe _k_ leading to
the prewash tank. Over the cylinder _i_ is a glass globe _l_, into which
opens a pipe _m_ for leading off fumes which may be promoted by a
compressed air jet from a pipe _r_ operating as an injector. Into an
opening of the glass dome _l_ is inserted a vessel _n_, which is connected
by a flexible pipe _p_ to the glycerine tank, and from the bottom of _n_,
which is perforated and covered with a disc perforated with holes
registering with those through the bottom, this disc being connected by a
stem with a knob _q_ by which it can be turned so as to throttle or cut
off passage of glycerine through the bottom. _s_ is a thermometer for
indicating the temperature of the contents of the vessel.
[Footnote A: Eng. Pat. 15,983, August 1901.]
[Illustration: FIG. 7.--NATHAN'S NITRATOR FOR NITRO-GLYCERINE. (_a_)
Nitrating Vessel; (_b_) to Separating Vessel; (_c_) to Drowning Tank;
(_e_) Nitrating Acids enter (_f_) to the Waste Acids; (_g_) Coils for
Compressed Air; (_h_) Pipes for Cooling Water; (_i_) Glass Cylinder; (_j_)
Outlet to _k_; (_k_) leading to Prewash Tank; (_l_) Glass Dome; (_m_) Pipe
to lead off for Escape of Fumes; (_n_) Vessel; (_p_) Pipe conveying
Glycerine; (_q_) Knob to turn off Glycerine; (_r_) Compressed Air Jet;
(_s_) Thermometer.]
In operating with this apparatus the nitrating acid is introduced into the
nitrating vessel by opening the cock of the pipe _e_. The glycerine is
then run in by introducing _n_ and opening the valve at its bottom, the
contents of the vessel being agitated by air blown through the
perforations of the pipe _g_. When the glycerine is all nitrated and the
temperature has slightly fallen, the circulation of the water through the
coils _h_ and the air-stirring are stopped, and the glycerine supply
vessel _n_ is removed. The nitro-glycerine as it separates from the acids
is raised by introducing by the pipe _f_ waste acid from a previous
charge, this displacing the nitro-glycerine upwards and causing it to flow
by the outlet, _j_ and pipe _k_ to the prewash tank. When nearly all the
nitro-glycerine has been separated in this manner the acids in the
apparatus may be run off by the pipe _b_ to an after separating vessel for
further settling, thus leaving the apparatus free for another nitration,
or the nitrating vessel itself may be used as an after separating bottle
displacing the nitro-glycerine with waste acid as it rises to the top, or
skimming off in the usual manner. When the separation of the nitro-
glycerine is complete the waste acid is run off and denitrated as usual, a
portion of it being reserved for the displacement of the nitro-glycerine
in a subsequent operation.
In a further patent (Eng. Pat. 3,020, 1903) the authors propose with the
object of preventing the formation and separation of nitro-glycerine in
the waste acids, after the nitro-glycerine initially formed in the
nitrating vessel has been separated and removed, to add a small quantity
of water to the waste acids; this is carried out as follows. A relatively
small quantity of water is added, and this prevents all further separation
of nitro-glycerine, and at the same time the strength of the waste acids
is so slightly reduced that their separation and re-concentration are not
affected. "After-separation" is thus done away with, and the nitro-
glycerine plant simplified and its output increased. After nitration
separation is commenced at a temperature such that when all the displacing
acid has been added, and the separation of the nitro-glycerine is
complete, the temperature of the contents of the nitrating vessel shall
not be lower than 15° C. A sufficient quantity of the displacing acid is
then run off through the waste-acid cock to allow of the remaining acids
being air-stirred without splashing over the top. A small quantity of
water, from 2 to 3 per cent. according to strength of acid; if waste
consists of sulphuric acid (monohydrate), 62 per cent.; nitric acid
(anhydrous), 33 per cent. and water 5 per cent.; temperature 15° C., then
2 per cent. of water is added; if waste acids contain less than 4 per
cent. of water of temperature lower than 15° C., from 3 to 5 per cent. of
water may have to be added. The water is added slowly through the
separator cylinder, and the contents of the nitrator air-stirred, but not
cooled, the temperature being allowed to rise slowly and regularly as the
water is added--usually about 3° C. for each per cent. of water added.
When air-agitation has been stopped, the acids are kept at rest for a
short time, in order to allow of any small quantity of initially formed
nitro-glycerine adhering to the coils and sides of the vessel rising to
the top. When this has been separated by displacement, the acids are ready
for denitration, or can be safely stored without further precaution.
~Separation.~--The nitro-glycerine, together with the mixed acids, flows
from the nitrating house to the separating house, which must be on a lower
level than the former. The separating house contains a large lead-lined
tank, closed in at the top with a wooden lid, into which a lead pipe of
large bore is fixed, and which is carried up through the roof of the
building, and acts as a chimney to carry off any fumes. A little glass
window should be fixed in this pipe in order that the colour of the
escaping fumes may be seen. The conduit conveying the nitro-glycerine
enters the building close under the roof, and discharges its contents into
the tank through the pipe G (Fig. 8). The tank is only about two-thirds
filled by the charge. There is in the side of the tank a small window of
thick plate glass, which enables the workman to see the level of the
charge, and also to observe the progress of the separation, which will
take from thirty minutes to one hour.
The tank should be in connection with a drowning tank, as the charge
sometimes gets very dangerous in this building. It must also be connected
by a conduit with the filter house, and also to the secondary separator by
another conduit. The tank should also be fitted with a compressed air
pipe, bent in the form of a loop. It should lie upon the bottom of the
vat. The object of this is to mix up the charge in case it should get too
hot through decomposition. A thermometer should of course be fixed in the
lid of the tank, and its bulb should reach down to the middle of the
nitro-glycerine (which rests upon the surface of the mixed acids, the
specific gravity of the nitro-glycerine being 1.6, and that of the waste
acids 1.7; the composition of the acids is now 11 per cent. HNO_{3}, 67
per cent. H_{2}SO_{4}, and 22 per cent. water), and the temperature
carefully watched.
[Illustration: FIG. 8.--SEPARATOR. _A_, Compressed Air Pipes; _G_, Nitro-
glycerine enters from Nitrator; _N_, Nitro-glycerine to _P_; _L_, Lantern
Window; _W_, Window in Side; _S_, Waste Acids to Secondary Separator; _T_,
Tap to remove last traces of Nitro-glycerine; _P_, Lead Washing Tank; _A_,
Compressed Air; _W_, Water Pipe; _N_, Nitro-glycerine from Separator.]
If nothing unusual occurs, and it has not been necessary to bring the
compressed air into use, and so disturb the process of separation, the
waste acids may be run away from beneath the nitro-glycerine, and allowed
to flow away to the secondary separator, where any further quantity of
nitro-glycerine that they contain separates out after resting for some
days. The nitro-glycerine itself is run into a smaller tank in the same
house, where it is washed three or four times with its own bulk of water,
containing about 3 lbs. of carbonate of soda to neutralise the remaining
acid. This smaller tank should contain a lead pipe, pierced and coiled
upon the bottom, through which compressed air may be passed, in order to
stir up the charge with the water and soda. After this preliminary
washing, the nitro-glycerine is drawn off into indiarubber buckets, and
poured down the conduit to the filter house. The wash waters may be sent
down a conduit to another building, in order to allow the small quantity
of nitro-glycerine that has been retained in the water as minute globules
to settle, if thought worth the trouble of saving. This, of course, will
depend upon the usual out-turn of nitro-glycerine in a day, and the
general scale of operations.
[Illustration: FIG. 9.--FILTERING AND WASHING PLANT. _W_, Lead Washing
Tank; _WP_, Water Pipe; _L_, Lid; _S_, Nitro-glycerine from Separator; _A,
B, C_, Filtering Tanks; _B2_, Indiarubber Bucket.]
~Filtering and Washing.~--The filter house (Fig. 9), which must of course
be again on a somewhat lower level than the separating house, must be a
considerably larger building than either the nitrating or separating
houses, as it is always necessary to be washing some five or six charges
at the same time. Upon the arrival of the nitro-glycerine at this house,
it first flows into a lead-lined wooden tank (W), containing a compressed
air pipe, just like the one in the small tank in the separating house.
This tank is half filled with water, and the compressed air is turned on
from half to a quarter of an hour after the introduction of the charge.
The water is then drawn off, and fresh water added. Four or five washings
are generally necessary. The nitro-glycerine is then run into the next
tank (A), the top of which is on a level with the bottom of the first one.
Across the top of this tank is stretched a frame of flannel, through which
the nitroglycerine has to filter. This removes any solid matters, such as
dirt or scum. Upon leaving this tank, it passes through a similar flannel
frame across another tank (B), and is finally drawn off by a tap in the
bottom of the tank into rubber buckets. The taps in these tanks are best
made of vulcanite.
At this stage, a sample should be taken to the laboratory and tested. If
the sample will not pass the tests, which is often the case, the charge
must be rewashed for one hour, or some other time, according to the
judgment of the chemist in charge. In the case of an obstinate charge, it
is of much more avail to wash a large number of times with small
quantities of water, and for a short time, than to use a lot of water and
wash for half an hour. Plenty of compressed air should be used, as the
compound nitric ethers which are formed are thus got rid of. As five or
six charges are often in this house at one time, it is necessary to have
as many tanks arranged in tiers, otherwise one or two refractory charges
would stop the nitrating house and the rest of the nitro-glycerine plant.
The chief causes of the washed material not passing the heat test are,
either that the acids were not clean, or they contained objectionable
impurities, or more frequently, the quality of the glycerine used. The
glycerine used for making nitro-glycerine should conform to the following
tests, some of which, however, are of greater importance than others. The
glycerine should--
1. Have minimum specific gravity at 15° C. of 1.261.
2. Should nitrify well.
3. Separation should be sharp within half an hour, without the separation
of flocculent matter, nor should any white flocculent matter (due to fatty
acids) be formed when the nitrated glycerine is thrown into water and
neutralised with carbonate of soda.
4. Should be free from lime and chlorine, and contain only traces of
arsenic, sulphuric acid, &c.
5. Should not leave more than 0.25 per cent. of inorganic and organic
residue together when evaporated in a platinum dish without ebullition
(about 160° C.) or partial decomposition.
6. Silver test fair.
7. The glycerine, when diluted one-half, should give no deposit or
separation of fatty acids when nitric peroxide gas is passed through it.
(Nos. 1, 2, 3, and 5 are the most essential.)
The white flocculent matter sometimes formed is a very great nuisance, and
any sample of glycerol which gives such a precipitate when tried in the
laboratory should at once be rejected, as it will give no end of trouble
in the separating house, and also in the filter house, and it will be very
difficult indeed to make the nitro-glycerine pass the heat test. The out-
turn of nitro-glycerine also will be very low. The trouble will show
itself chiefly in the separating operation. Very often 2 or 3 inches will
rise to the surface or hang about in the nitro-glycerine, and at the point
of contact between it and the mixed acids, and will afterwards be very
difficult to get rid of by filtration. The material appears to be partly
an emulsion of the glycerine, and partly due to fatty acids, and as there
appears to be no really satisfactory method of preventing its formation,
or of getting rid of it, the better plan is not to use any glycerine for
nitrating that has been found by experiment upon the laboratory scale to
give this objectionable matter. One of the most useful methods of testing
the glycerine, other than nitrating, is to dilute the sample one-half with
water, and then to pass a current of nitric peroxide gas through it, when
a flocculent precipitate of elaïdic acid (less soluble in glycerine than
the original oleic acid) will be formed. Nitrogen peroxide, N_{2}O_{4}, is
best obtained by heating dry lead nitrate (see Allen, "Commercial Organic
Analysis," vol. ii., 301).
When a sample of nitro-glycerine is brought to the laboratory from the
filter house, it should first be examined to see that it is not acid.[A] A
weak solution of Congo red or methyl orange may be used. If it appears to
be decidedly alkaline, it should be poured into a separating funnel, and
shaken with a little distilled water. This should be repeated, and the
washings (about 400 c.c.) run into a beaker, a drop of Congo red or methyl
orange added, and a drop or so of N/2 hydrochloric acid added, when it
should give, with two or three drops at most, a blue colour with the Congo
red, or pink with the methyl orange, &c. The object of this test is to
show that the nitro-glycerine is free from any excess of soda, i.e., that
the soda has been properly washed out, otherwise the heat test will show
the sample to be better than it is. The heat test must also be applied.
[Footnote A: A. Leroux, _Bul. Soc. Chim. de Bel._, xix., August 1905,
contends that experience does not warrant the assumption that free acid is
a source of danger in nitro-glycerine or nitro-cellulose; free alkali, he
states, promotes their decomposition.]
Upon leaving the filter house, where it has been washed and filtered, and
has satisfactorily passed the heat test, it is drawn off from the lowest
tank in indiarubber buckets, and poured down the conduit leading to the
precipitating house, where it is allowed to stand for a day, or sometimes
longer, in order to allow the little water it still contains to rise to
the surface. In order to accomplish this, it is sufficient to allow it to
stand in covered-in tanks of a conical form, and about 3 or 4 feet high.
In many works it is previously filtered through common salt, which of
course absorbs the last traces of water. It is then of a pale yellow
colour, and should be quite clear, and can be drawn off by means of a tap
(of vulcanite), fixed at the bottom of the tanks, into rubber buckets, and
is ready for use in the preparation of dynamite, or any of the various
forms of gelatine compounds, smokeless powders, &c., such as cordite,
ballistite, and many others.
Mikolajezak (_Chem. Zeit._, 1904, Rep. 174) states that he has prepared
mono- and di-nitro-glycerine, and believes that the latter compound will
form a valuable basis for explosives, as it is unfreezable. It is stated
to be an odourless, unfreezable oil, less sensitive to percussion,
friction, and increase of temperature, and to possess a greater solvent
power for collodion-cotton than ordinary nitro-glycerine. It can thus be
used for the preparation of explosives of high stability, which will
maintain their plastic nature even in winter. The di-nitro-glycerine is a
solvent for tri-nitro-glycerine, it can therefore be mixed with this
substance, in the various gelatine explosives in order to lower the
freezing point.
~The Waste Acids.~--The waste acids from the separating house, from which
the nitro-glycerine has been as completely separated as possible, are run
down the conduit to the secondary separator, in order to recover the last
traces of nitro-glycerine that they contain. The composition of the waste
acids is generally somewhat as follows:--Specific gravity, 1.7075 at 15°
C.; sulphuric acid, 67.2 per cent.; nitric acid, 11.05 per cent.; and
water, 21.7 per cent., with perhaps as much as 2 per cent. of nitric
oxide, and of course varying quantities of nitro-glycerine, which must be
separated, as it is impossible to run this liquid away (unless it can be
run into the sea) or to recover the acids by distillation as long as it
contains this substance. The mixture, therefore, is generally run into
large circular lead-lined tanks, covered in, and very much like the
nitrating apparatus in construction, that is, they contain worms coiled
round inside, to allow of water being run through to keep the mixture
cool, and a compressed air pipe, in order to agitate the mixture if
necessary. The top also should contain a window, in order to allow of the
interior being seen, and should have a leaden chimney to carry off the
fumes which may arise from decomposition. It is also useful to have a
glass tube of 3 or 4 inches in diameter substituted for about a foot of
the lead chimney, in order that the man on duty can at any time see the
colour of the fumes arising from the liquid. There should also be two
thermometers, one long one reaching to the bottom of the tank, and one to
just a few inches below the surface of the liquid.
The nitro-glycerine, of course, collects upon the surface, and can be
drawn off by a tap placed at a convenient height for the purpose. The
cover of the tank is generally conical, and is joined to a glass cylinder,
which is cemented to the top of this lead cover, and also to the lead
chimney. In this glass cylinder is a hole into which fits a ground glass
stopper, through which the nitro-glycerine can be drawn off. There will
probably never be more than an inch of nitro-glycerine at the most, and
seldom that. It should be taken to the filter house and treated along with
another charge. The acids themselves may either be run to waste, or better
treated by some denitration plant. This house probably requires more
attention than any other in the danger area, on account of the danger of
the decomposition of the small quantities of nitro-glycerine, which, as it
is mixed with such a large quantity of acids and water, is very apt to
become hot, and decomposition, which sets up in spots where a little
globule of nitro-glycerine is floating, surrounded by acids that gradually
get hot, gives off nitrous fumes, and perhaps explodes, and thus causes
the sudden explosion of the whole. The only way to prevent this is for the
workman in charge to look at the thermometers _frequently_, and at the
colour of the escaping fumes, and if he should notice a rise of
temperature or any appearance of red fumes, to turn on the water and air,
and stir up the mixture, when probably the temperature will suddenly fall,
and the fumes cease to come off.
The cause of explosions in this building is either the non-attention of
the workmen in charge, or the bursting of one of the water pipes, by which
means, of course, the water, finding its way into the acids, causes a
sudden rise of temperature. If the latter of these two causes should
occur, the water should at once be shut off and the air turned on full,
but if it is seen that an explosion is likely to occur, the tank should at
once be emptied by allowing its contents to run away into a drowning tank
placed close outside the house, which should be about 4 feet deep, and
some 16 feet long by 6 feet wide; in fact, large enough to hold a
considerable quantity of water. But this last course should only be
resorted to as a last extremity, as it is extremely troublesome to recover
the small quantity of nitro-glycerine from the bottom of this tank, which
is generally a bricked and cemented excavation some few yards from the
house.
It has been proposed to treat these waste acids, containing nitro-
glycerine, in Mr M. Prentice's nitric acid retort. In this case they would
be run into the retort, together with nitrate of soda, in a fine stream,
and the small quantity of nitro-glycerine, coming into contact with the
hot mixture already in the retort, would probably be at once decomposed.
This process, although not yet tried, promises to be a success. Several
processes have been used for the denitration of these acids.
~Treatment of the Waste Acid from the Manufacture of Nitro-Glycerine and
Gun-Cotton.~--The composition of these acids is as follows:--
Nitro-glycerine and Gun-cotton
Waste Acid.
Sulphuric acid 70 per cent. 78 per cent.
Nitric acid 10 " 12 "
Water 20 " 10 "
The waste acid from the manufacture of gun-cotton is generally used direct
for the manufacture of nitric acid, as it contains a fairly large amount
of sulphuric acid, and the small amount of nitro-cellulose which it also
generally contains decomposes gradually and without explosion in the
retort. Nitric acid may be first distilled off, the resulting sulphuric
acid being then added to the equivalent amount of nitrate of soda. Nitric
acid is then distilled over and condensed in the usual way. Very often,
however, the waste acid is added direct to the charge of nitrate without
previously eliminating the nitric acid. The treatment of the waste acid
from the manufacture of nitro-glycerine is somewhat different. The small
amount of nitro-glycerine in this acid must always be eliminated. This is
effected either by allowing the waste acid to stand for at least twenty-
four hours in a big vessel with a conical top, where all the nitro-
glycerine which will have separated to the surface is removed by skimming;
or, better still, the "watering down process" of Col. Nathan may be
employed. In Nathan's nitrator every existing trace of nitro-glycerine is
separated from the acids in a few hours after the nitration, and any
further formation of nitro-glycerine is prevented by adding about 2 per
cent. of water to the waste acids, which are kept agitated during the
addition. The waste acid, now free from nitro-glycerine, but which may
still contain organic matter, is denitrated by bringing it into contact
with a jet of steam. The waste acid is passed in a small stream down
through a tower of acid-resisting stoneware (volvic stone), which is
closely packed with earthenware, and at the bottom of which is the steam
jet. Decomposition proceeds as the acid meets the steam, nitric and
nitrous acids are disengaged and are passed out at the top of the tower
through a pipe to a series of condensers and towers, where the nitric acid
is collected. The nitrous acid may be converted into nitric acid by
introducing a hot compressed air jet into the gases before they pass into
the condensers. Weak sulphuric acid of sp. gr. 1.6 collects in a saucer in
which the tower stands, and is then passed through a cooling worm. The
weak sulphuric acid, now entirely free from nitric and nitrous acids, may
be concentrated to sp. gr. 1.842 and 96 per cent. H_{2}SO_{4} by any of
the well-known processes, e.g., Kessler, Webb, Benker, Delplace, &c., and
it may be used again in the manufacture of nitro-glycerine or gun-cotton.
Two points in the manufacture of nitro-glycerine are of the greatest
importance, viz., the purity of the glycerine used, and the strength and
purity of the acids used in the nitration. With regard to the first of
these, great care should be taken, and a complete analysis and thorough
examination, including a preliminary experimental nitration, should always
be instituted. As regards the second, the sulphuric acid should not only
be strong (96 per cent.), but as free from impurities as possible. With
the nitric acid, which is generally made at the explosive works where it
is used, care must be taken that it is as strong as possible (97 per cent.
and upwards). This can easily be obtained if the plant designed by Mr
Oscar Guttmann[A] is used. Having worked Mr Guttmann's plant for some
time, I can testify as to its value and efficiency.
[Footnote A: "The Manufacture of Nitric Acid," _Jour. Soc. Chem. Ind._,
March 1893.]
Another form of nitric acid plant, which promises to be of considerable
service to the manufacturer of nitric acid for the purpose of nitrating,
is the invention of the late Mr Manning Prentice, of Stowmarket. Through
the kindness of Mr Prentice, I visited his works to see the plant in
operation. It consists of a still, divided into compartments or chambers
in such a manner that the fluid may pass continuously from one to the
other. The nitric acid being continuously separated by distillation, the
contents of each division vary--the first containing the full proportion
of nitric acid, and each succeeding one less of the nitric acid, until
from the overflow of the last one the bisulphate of soda flows away
without any nitric acid. The nitrate of soda is placed in weighed
quantities in the hopper, whence it passes to the feeder. The feeder is a
miniature horizontal pug-mill, which receives the streams of sulphuric
acid and of nitrate, and after thoroughly mixing them, delivers them into
the still, where, under the influence of heat, they rapidly become a
homogeneous liquid, from which nitric acid continuously distils.
Mr Prentice says: "I may point out that while the ordinary process of
making nitric acid is one of fractional distillation by time, mine is
fractional distillation by space." "Instead of the operation being always
at the same point of space, but differing by the successive points of
time, I arrange for the differences to take place at different points of
space, and these differences exist at one and the same points of time." It
is possible with this plant to produce the full product of nitric acid of
a gravity of 1.500, or to obtain the acid of varying strengths from the
different still-heads. One of these stills, capable of producing about 4
tons of nitric acid per week, weighs less than 2 tons. It is claimed that
there is by their use a saving of more than two-thirds in fuel, and four-
fifths in condensing plant. Further particulars and illustrations will be
found in Mr Prentice's paper (_Journal of the Society of Chemical
Industry_, 1894, p. 323).