Читать книгу Nitro-Explosives: A Practical Treatise - P. Gerald Sanford - Страница 26

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—