Nitro Explosives: A Practical Treatise by P. Gerald Sanford

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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 deg. 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 deg. 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 deg. 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 deg. 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 deg. 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 deg. 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 deg. 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 deg. 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.

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