AMERICAN PRODUCTION OF MILITARY HIGH EXPLOSIVES AND THEIR RAW MATERIALS
By Lieut. Commander Carleton H. Wright, U. S. Navy
When H. M. S. Hampshire was sunk by a German mine on June 5, 1916, Germany rejoiced and gloom pervaded England, for Lord Kitchener, the man on whom Great Britain relied for guidance and leadership in the great struggle, went down with the ship. Now, however, it is generally recognized that his death at that time was a most fortunate occurrence for Great Britain and her allies, for Kitchener in his capacity of Secretary of State for War controlled in large part England's production of munitions, and his failure to grasp the fact that under the new conditions of warfare high explosives must be produced and supplied to the armies in the field in unprecedented amounts had already cost the British forces dearly.
Before the outbreak of the World War none of the combatants had realized how great the use of high explosives would be, but the Germans and also the French had been quick to grasp the significance of the changed conditions, and had taken prompt steps to raise their production of high explosives to the maximum. The British armies in the field also early realized the importance of adequate supplies of high explosive shell, but their appeals for increased supplies met with but little response, for Kitchener had received his training under far different conditions and he could not realize the revolutionary changes that had taken place.
After his death Great Britain joined the other combatants in bending every energy toward increasing the production of high explosives. In order to augment the supply the various belligerents developed on a large manufacturing basis many explosives which had hitherto not been deemed worthy of consideration and maintained a continuous search for new sources of supply. One result of the continuously increasing demand was that the Allies soon turned to the United States for additional supplies.
Prior to that time this country had not been a large producer of explosives adapted to military use, or even of the raw materials for their manufacture. We did, however, have vast undeveloped resources, and the high prices offered by the Allies greatly stimulated production, both of the raw materials and of the manufactured explosives. Principally because of the great saving of valuable cargo space, the Allies encouraged the manufacture of the finished explosives in this country rather than having us furnish them with only the raw materials. This policy resulted in the building of many new explosives plants here and the rapid expansion of those already in existence.
Thus American production of military explosives rapidly increased and the way was being prepared so that, upon our entrance into the war, the upward trend of production was merely greatly accelerated to meet the requirements of our own military and naval forces, while still continuing to furnish vast supplies to the Allies. Some idea of our expansion as a supplier of military explosives may be had from the fact that in 1914 we produced just a little over twenty-one million pounds of smokeless powder and other military explosives, while at the time of the armistice our production of high explosives alone was at the rate of seven hundred and twenty-five million pounds per year and that of smokeless powder was even larger.
At the present time while the record of our war achievements is fresh in our minds it is well to consider in detail our production of military high explosives, with a view to learn what production we may expect in case of need in the future; where the material for the manufacture of our explosives is to be obtained; and wherein our potential domestic supplies of raw materials should be developed to render us, so far as possible, independent of imports.
High Explosives
An explosive has been denned by Marshall as "a solid or liquid substance or mixture of substances which is liable, on application of heat or of a blow to a small portion of the mass, to be converted in a very short interval of time into other more stable substances, principally gaseous, with the evolution of a considerable amount of heat."
Substances of this type which are used by our military forces may be divided into two general classes, "progressive explosives" and "high explosives." The former are the so-called powders used to propel the projectile from the gun in the firing of small arms and cannon. Their rate of combustion when used as propellants is very much lower than the rate of detonation of the high explosives. The latter, which constitute the bursting charge of projectiles', torpedoes, submarine mines, etc., are designed to explode only when in the vicinity of the enemy and consequently a high velocity of explosion is desired to insure complete fragmentation in the case of projectiles, or in the case of underwater explosions the maximum blow upon the hull of the enemy .ship. Practically speaking, no substance is considered as a military high explosive unless the velocity of detonation is at least three thousand meters per second.
The properties of high explosives which are of chief interest are the power, sensitiveness, velocity of explosion, and stability.
High power is of the greatest importance, since it is desired to get the maximum explosive effect from a given weight of explosive. In the case of shell fillers, the density of the material, as affecting the power, possible from the limited space available, is also of importance.
The degree of sensitiveness must lie within certain definite limits, depending on the use to which the explosive is to be put. The substance must not be subject to premature detonation from shocks it may receive in service, yet it must not be so insensitive that there will be danger of failure to function under the conditions it will encounter in action.
Closely allied to the question of sensitiveness is the subject of detonators arid boosters. A detonator is an explosive Used to initiate.cn explosion in another substance. Since the material in the detonator is always more sensitive than that in the main charge the size of the detonator is always kept at the minimum consistent with proper functioning.
Usually a booster or boosters of material more readily detonated than the main charge is interposed between the detonator and the charge. The detonator first explodes the booster and then the latter explodes the main charge. It has been shown that improper detonators and boosters may not only cause complete failure to explode, but also result in incomplete detonation or "low order" explosions in other cases where outward appearances indicate satisfactory functioning. The modern tendency is to adopt as main bursting charges substances which are more and more difficult to detonate, and consequently the use of efficient boosters and detonators is becoming of constantly increasing importance.
The velocity of explosion and the closely related property, "brisance" which has been defined as the rate of increase to maximum pressure, are of great importance, for upon them depend the proper fragmentation of projectiles and the intensity of the blow in under water explosions.
An explosive for military use must be stable under the worst conditions it will encounter in storage or in service. An unstable explosive cannot be considered, because it may either fail to function when desired or else will be a source of danger in handling. It might even exhibit both of these undesirable attributes.
The Influence of Supply on the Choice of Explosives
There are a rather large number of substances known to the chemists of the world which would be almost equally satisfactory as military explosives. The nature of the raw materials, the available supply of these materials, and the cost of the finished substance vary within wide limits, however, and the two factors of available supply and cost must govern the choice of explosives when other factors are even approximately equal.
Considerations of national safety demand that so far as possible the materials for explosives manufacture be articles of domestic production. When the difference in cost in favor of an explosive made from imported materials is great there will be a strong tendency, particularly on the part of some legislators, to favor the cheaper material, but this does not alter the fact that the choice of an explosive made from imported materials is fundamentally unsound if a satisfactory explosive can possibly be produced from domestic supplies.
In case it is necessary to import materials for explosives, the location of the world supply must be considered. When any choice is available, it is obviously best to select a material the supply of which is not controlled by any one nation. Likewise a supply which is not subject to interruption because of stoppage of ocean-borne commerce is highly to be desired.
In the World War we find frequent examples of the use of explosives which are rather unsatisfactory from a military point of view, but their use was forced upon the belligerents because the normal supplies of raw materials were interrupted, or because the available supplies of the raw materials required in the manufacture of the explosives they preferred were inadequate to supply their needs. Examples of such substitutions are the use of wood cellulose instead of cotton by the Germans and the use of nitroethane, trinitrocresol, trinitronaphthalene, etc., by the Allies.
The price of raw materials is of course regulated to a large extent by the age old law of supply and demand. Under the heading of supply must be considered not only the extent but also the location of the world's supply, for the Germans have shown in the dye industry, the potash industry, and the like, that a nation which is favored with natural advantages can, if she so desires, manipulate prices in such a manner as practically to prohibit the development of natural resources in other countries. A consideration of available resources must also take into account the purity of the materials as found, for the manufacture of explosives requires materials of a very high state of purity, and the cost of purification may eliminate from consideration the supply of material from certain sources.
Non-military demands for the same material required for the manufacture of a certain explosive, or for similar material, may favor or may operate against the adoption of that particular explosive. If the supply is insufficient to meet the normal demands the price will probably be prohibitively high. Upon the other hand, the demand from commercial sources may cause the development of new sources of supply, and thus favor the adoption of that explosive, particularly if the new sources of supply are domestic. Many of the materials most satisfactory for the manufacture of explosives are by-products of other industrial processes, and naturally increased demand for the principal products of the process renders the by-products available in increased quantities and at attractive prices.
In any consideration of the sources of supply of raw materials it is essential that due attention be given to the fact that rapid progress is being made in the accumulation of chemical knowledge, and that new chemical processes are being developed which may practically revolutionize an industry. A most notable example of this as affecting explosives is the development of processes by which benzol may be used as the raw material for the manufacture of picric acid. The discovery of such a process vastly increased this country's possible production of high explosives.
Even more revolutionary is the development of synthetic methods for the fixation of atmospheric nitrogen in Germany. It is worthy of note that as soon as these methods had been developed to a point of quantity production, rendering Germany independent of nitrates from Chili, she plunged the world into war. In marked contrast to this, it is known that at the time of the Agadir incident the German chemists informed the rulers of the empire that war could not be successfully waged until such synthetic processes had been developed, and consequently hostilities were at that time avoided.
The Principal High Explosives Manufactured in the United States
During the World War, as has previously been stated, large quantities of smokeless powder and high explosives for the Allies were manufactured in this country. In this paper only the production of high explosives will be discussed, for this is the branch of the explosives industry that made the most startling advances after we entered the war as a combatant. Since one of the objects of this article is to see what quantity of high explosives this country is capable of producing in case of emergency, the amounts of material made for" the Allies will be included in the totals to be given hereafter. Although the Allies favored some explosives that have never been liked by our own forces, it is probable that in case of need in the future our production would follow the same general lines that it did in the late war.
The principal high explosives manufactured here for military use will be discussed separately:
1. Nitrated Aromatic Compounds.—Most of the modern high explosives are in whole or in part the product of the nitration of the aromatic compounds formed principally in the destructive distillation of bituminous coal. The most satisfactory of these explosives are the products of the trinitration of substances having a single benzene nucleus, e. g., trinitrobenzene, trinitrotoluene, trinitrophenol, and trinitroxylene. It should be noted that in all of these the isomer most readily formed, and the one most stable of all those possible, is the one in which the three nitro groups are symmetrically arranged around the benzene ring.
Mono- and di-nitro bodies are ordinarily not in themselves satisfactory as high explosives, but they are used extensively in mixed commercial explosives, and to some extent in mixed military explosives, particularly in France and Germany. They have not been used to any important extent in military explosives in this country.
(a) Trinitrobenzene.—Trinitrobenzene is a very satisfactory high explosive, but because of the difficulty of nitrating benzene and the low yields obtained, its manufacture is so expensive as to be prohibitive. Toluene, phenol, and xylene are nitrated much more easily than benzene, as the presence of a substituent in the benzene ring facilitates the entrance of other substituents.
(b) Trinitrotoluene.—The widespread use of trinitrotoluene is indicated by the number of names under which it is known. The principal of these are TNT, trinitrotoluol, trotyl, tritolo, trinol, and trilite.
Although this explosive has only recently come into general use it has been waging a winning fight against picric acid for favor as a shell filler, and against guncotton for use in mines and torpedoes.
TNT is slightly less powerful than picric acid, but this disadvantage is more than outweighed by several distinct advantages. First of these is the fact that TNT, unlike picric acid, does not form sensitive salts when in contact with the heavy metals. Second is the fact that nitration of toluene is considerably easier than that of phenol, and the yield considerably nearer the amount that should theoretically be obtained. Still another advantage is the lower melting point of TNT, enabling it to be much more easily cast direct into shell cavities, etc.
TNT is used for bursting charges of projectiles, both by itself and mixed with other substances; for main charges of submarine mines, torpedoes, depth charges, and bombs; and it is also used in boosters. In addition it enters into the manufacture of many mixed explosives, the principal ones in this country being amatol and toxyl.
During the war, in spite of our rapidly increasing production, the supply of TNT was never equal to the demand. The limiting factor in our production throughout our participation in the war was the lack of a supply of toluene sufficient to supply our needs.
In Fig. 1 is shown our increasing production in 1918. For purposes of comparison the production in August, 1914, and April, 1917, is also given.
For the manufacture of one pound of TNT the following raw material is required: Toluene, 0.068 gal.; nitric acid (100 per cent), 1.11 pounds; sulphuric acid (100 per cent), 0.31 pounds. Besides these, alcohol and benzene are required in the purification by crystallization.
(c) Picric Acid and Ammonium Picrate.—Like TNT, trinitrophenol or picric acid is known under various names in different countries. The most common of these are P. A., lyddite, melinite, shimosite, and pertite.
Until recently picric acid or its ammonium salt were almost the only substances used by the nations of the world as a shell filler. Even now it is more extensively used for this purpose than any other material, and will no doubt continue to be for some time in the future, because the raw materials for the manufacture of picric acid—phenol and benzene—are available in great quantities.
Picric acid itself is a very satisfactory explosive for use in projectiles in practically all respects except one—that it, forms extremely sensitive salts when in contact with the heavy metals, especially lead. In recent years few serious accidents have occurred from this source because proper precautions have been taken to avoid any opportunity for the formation of such salts, but the necessity for care is always present.
Ammonium picrate is also a satisfactory explosive. The advantage in the use of ammonium picrate in place of picric acid is the reduction of the danger of the formation of metallic picrates.
Picric acid itself has never been adopted as a military high explosive in this country, but it has been in great demand in Europe, particularly on the part of France. When the Allies turned to us for an augmentation of their supplies in 1915 the prospect of their receiving much assistance looked far from promising. To begin with, all picric acid was at that time made from phenol and we had never produced even enough phenol to satisfy our own requirements for the supply of commercial needs. The war naturally stopped exports to us from the belligerents and an acute shortage existed. In order to supply the phenol required in the synthetic manufacture of the resin used in making phonograph records, the Edison research laboratory began the study of synthetic methods for the manufacture of phenol from benzene. Within a very short time they had perfected such a process, and a plant was built with sufficient capacity not only to supply all their needs but to leave a large excess for sale.
Here was the Allies' opportunity, but the alert German organization under Dr. Albert was quicker to see the possibilities than they were, with the result that a contract was signed requiring the delivery of all phenol made in excess of the requirements of the Edison Company to firms designated by Dr. Albert's agents. These firms, which were subsidiaries of the great German chemical houses, converted the phenol into salicylic acid, perfumes, flavoring extracts, and other products which were useless to the Allies in their search for explosives. This operation not only netted the German organization a profit of more than eight hundred thousand dollars from the sale of the products they manufactured, but what was much more important to them, it prevented the manufacture of more than four and one-half million pounds of picric acid which the Allies would otherwise have secured.
Consequently the Allies had to await the construction of other synthetic phenol plants, and the development of the by-product industry before they could obtain large supplies of picric acid in this country. Production of picric acid for them on a large scale began in 1916, however, and we contributed important supplies both before and after we entered the war. In the later stages of the struggle production was not limited by shortage of raw material as only a small part of our total production of benzene went into the manufacture of picric acid.
Fig. 2 shows graphically our production of picric acid in 1918. Practically all of this was for delivery to the Allies, especially the French, whose demands for this explosive seemed to be almost insatiable. The production of picric acid in the United States prior to the World War was negligible, with the little being made used largely as a dye.
In Fig. 3 is shown our production of ammonium picrate in 1918. Our production of this material in 1914 was also hardly worthy of mention. Our rate of production at the time we entered the war is given for the purpose of comparison.
For the manufacture of one pound of picric acid the following material is required: Phenol, 0.566 pounds (the equivalent of 0.110 gal. benzene and 2.20 pounds of 100 per cent sulphuric acid); nitric acid (100 per cent), 1.34 pounds; sulphuric acid (100 per cent) 2.01 pounds.
For the manufacture of one pound of ammonium picrate the following is required: Picric acid 0.99 lb.; and ammonia 0.084 lb.
(d) Trinitroxylene.—From 1 its physical properties trinitroxylene or TNX would appear to be most unfavorable for use as a military high explosive. The melting point of the predominating isomer is very high, 1820 C, making it impossible to load by direct casting. Moreover this compound is almost insoluble in other lower melting point nitro bodies at low temperatures, such as are preferable for casting, seemingly precluding the casting of such a mixture. It has not more than 80 per cent the strength of TNT and it is much less sensitive to detonation.
The acute situation which developed in the TNT supply in the summer of 1917, however, made it necessary to consider the use even of material which appeared unfavorable. Under these conditions the du Pont Company began experiments with mixtures of TNX with TNT in cast charges.
Rather to the surprise of those concerned, TNX proved to be almost ideal for the purpose. When 30 to 50 parts of TNX were suspended in 70 to 50 parts of TNT at 100° C, a sufficiently fluid mass was obtained to permit direct casting. The castings when cooled proved to be non-hygroscopic, free from air holes, and without segregation of the components. The cast mixture could be detonated with smaller boosters of tetryl than were required for refined TNT, and the tests showed an explosive force approaching that of straight TNT. Moreover it was found that purification of the TNX was not necessary as the crude material was just as satisfactory as the refined.
Consequently immediate steps were taken to develop a manufacturing process for use in large scale production. As this was nearing completion negotiations were entered into with the Navy Department, which eventually resulted in the drawing of a contract requiring the delivery of 2,500,000 pounds of TNX each month beginning with December, 1918.
Work was promptly begun on the construction of the plant and at the time of the armistice two of the five units of the plant were in full production and the other three either nearing completion or in partial production. A total of only 228,000 pounds of TNX was delivered, but it is certain that the large supply of this material which would have been available had the war lasted even a few months longer would have been most welcome.
Except in case of national emergency, the manufacture of TNX will not be carried on, for it is not so satisfactory an explosive as TNT, but the perfection of the manufacturing processes on a full scale is a distinct national asset, for we are now enabled, in case of future need, practically to extend our TXT supply by one-fifth.
Materials required for the manufacture of TNX are xylene (free from paraffines and naphthenes), nitric and sulphuric acids, and sodium carbonate. The exact amounts can not be given, since the information belongs to the Du Pont Company.
Tetryl or trinitrophenylmethylnitramine is extensively used as a booster, as it has been found to be a most satisfactory substance for this purpose in the detonation of TNT and other nitro aromatic compounds. The high cost of its manufacture prevents its use as a main bursting charge, although it would otherwise be satisfactory for this purpose.
Because of its use being limited to the loading of boosters, the quantity of tetryl required is naturally much smaller than that of the other nitro aromatic compounds previously discussed.
Prior to the World War the amount of tetryl made in the United States was negligible. Before we entered the war considerable quantities were made for the Allies, but the really rapid increase in production was not made until 1918. Our production in that year is shown in Fig. 4.
For the manufacture of one pound of tetryl the following material is required: Dimethylaniline, 0.45 pounds; sulphuric acid (100 per cent), 4.47 pounds; nitric acid (100 per cent), 3.87 pounds.
Note.—One pound of dimethylaniline requires two pounds of aniline and 0.23 pound of methyl alcohol for its manufacture.
(f) Other Nitro-Aromatic Compounds.—Many other nitroaromatic compounds are explosive substances, and some of them were used by European nations during the World War. Probably the most important of these are trinitrocresol, trinitroanisole, trinitronaphthalene, and tetranitroaniline, used principally by the French and Russians; and hexanitrodiphenylamine, used by the Germans in mixture with TNT as a bursting charge for torpedoes and mines. The first two of these have been tried out on a small scale in this country, but found unsatisfactory. The expense of manufacture of all except the nitrated. naphthalenes has been very great in comparison with TNT, and none of them have sufficient advantage over TNT to displace it as a main bursting charge in this country. Just prior to the armistice the manufacture of tetranitroaniline was, however, begun in the United States. The plant and equipment were already in existence, having been built to manufacture this material for the Russians before we entered the war. As tests had shown it to be practically as efficient as tetryl for boosters, manufacture was begun with the idea of augmenting our supply of material for boosters. About 8000 pounds were delivered, but none of this was used because of the cessation of hostilities.
Just recently the Du Pont Company has perfected a process for the manufacture of hexanitrodiphenylamine from dinitromono chlor benzene and analine, which gives a very high yield at low cost. Hexanitrodiphenylamine has been shown by test to be more efficient than Grade " A " TNT as a booster, and almost equal to TNA and tetryl for this purpose. As it is more stable than either of the latter, and the new method of manufacture makes it very much cheaper than other satisfactory booster materials, it seems probable that the future will see us using hexanitrodiphenylamine in large quantities in the loading of boosters.
Another high explosive which may in the future be extensively manufactured here, is parazol, or dinitroparadichlorbenzene. In the manufacture of phenol or of picric acid from benzene the first stage is the formation of monochlorbenzene by the action of chlorine gas on benzene. At this stage a considerable quantity of dichlorbenzene, mostly para, is always formed, in spite of efforts to obtain the maximum yield of the monochlor body. The paradichlorbenzene ,which is otherwise a waste body can easily be nitrated to the dinitro stage. The product, parazol, is a stable body which can, when mixed with TNT, be detonated. The result of such detonation is a high order explosion with evolution of large quantities of poisonous gas.
2. Non-Aromatic Explosives.—Although recent years have seen the rapid rise to a position of first importance of the nitroaromatic explosives, the demand for high explosives in the late war was so great that the production of the other high explosives also increased rapidly. In time of peace the non-aromatic explosives are manufactured in great quantity for commercial uses, while the use of the nitro-aromatic compounds for such purposes has in the past been relatively unimportant.
(a) Ammonium Nitrate.—The principal of these explosives of other than aromatic origin, at least in point of quantity manufactured for military use in the late war, is ammonium nitrate. In the United States its principal use was as a constituent of "80-20" amatol (80 per cent NH4NO3, 20 per cent TNT), which was extensively used as a shell filler.
Ammonium nitrate is not so powerful as the principal nitro aromatic high explosives, is hygroscopic, and is prone to give low order explosions: but it appears to be the only shell filler that can be produced in sufficient amounts to supply our needs.
The cost is low because of the relative cheapness of the rawmaterials and the simplicity of the processes of manufacture. It may be prepared by simply neutralizing nitric acid with ammonia, or by double decomposition between ammonium sulphate and sodium nitrate. The simplicity of the manufacturing operations greatly facilitates rapid increase of production in case of necessity.
Ammonium nitrate is a constituent of an important class of dynamites, and consequently our production of this substance in 1914 was of respectable proportions. Our extremely rapid increase in production in 1918 is shown in Fig. 5. For purposes of comparison our production in 1914 and at the time we entered the war is also given.
The material required for the manufacture of one pound of ammonium nitrate by the neutralization process is: Ammonia, 0.23 pound; nitric acid (100 per cent), 0.813 pound.
(b) Nitroglycerine.—In time of peace nitrogylcerine is made in greater quantities than all other high explosives. In time of war it is still of great national importance because of the extensive use of dynamite in the essential industries, but it is not adapted to military use and is not a constituent of any important military high explosives. It is however an important component of the so-called "two-base" (nitroglycerine-nitrocellulose) type of smokeless powders, such as cordite, which many other nations use as propellants. As such it does not, however, properly come within the province of this article.
(c) Gun Cotton.—Gun cotton and nitroglycerine were both discovered in 1846, and for many years they were the only important high explosives. Until recently gun cotton was used almost universally as the main charge for mines and torpedoes. Now, however, the nitro-aromatic compounds, especially TNT, have largely replaced it and gun cotton has become of minor importance as a military high explosive.
Considerable amounts were made in this country during the war, but this was almost entirely for delivery to the Allies. Unlike the other high explosives used for military purposes it shows no material increase of production in 1918, the average being a little over 2,100,000 pounds per month, and the October production being actually less than that in July.
Gun cotton is less powerful and less brisant than TNT, and it is subject to slow deterioration, particularly when it is in the dry state, which necessitates frequent inspection and constant vigilance. It is safe to state that it will be unimportant as a military high explosive in case of future wars.
Material required for the manufacture of one pound of gun cotton is: Cotton, 0.70 pounds; sulphuric acid (100 per cent), 0.68 pound; nitric acid (100 per cent), 1.12 pounds.
(d) Nitro Starch.—In the early stages of the war, because of the apparent shortage of TNT and NH4N03 then existing, it was necessary to develop an explosive for filling grenades, trench mortar shell and drop bombs. To meet this need the Trojan Powder Co. developed a nitro-starch explosive which was adapted to this use. Nitro-starch explosives had been under investigation by other manufacturers for a number of years, but the difficulties incident to the manufacture and purification of nitro-starch had not previously been overcome.
The Trojan Powder Co., operating under a secret process, overcame these difficulties' and all nitro starch explosives used in the war were made by this company, although another nitrostarch explosive, manufactured by the Du Pont Co., was developed during the war and authorized for use.
Our country was the only one that used nitro-starch explosives during the war, but the results obtained in service were so satisfactory that there is reason to assume that if similar need were to arise in the future nitro-starch explosives would again be used by us for filling grenades, and for similar uses. The cost of the raw materials is low, and the use of these materials does not interfere with the manufacture of other types of explosives.
No nitro-starch explosives were manufactured, except in experimental lots, in this country prior to the year 1918. Our production by months during that year is shown in Fig. 6.
(e) Fulminate of Mercury.—Although the quantity of fulminate used is small, the importance of this substance is evident from the fact that the detonation of every one of our high explosive shells, torpedoes, mines, and bombs is dependent upon the proper functioning of the fulminate in the detonator.
Nobel's discovery of the peculiar ability of fulminate to initiate a high order explosion in nitroglycerine was the first step in the development of high explosives. Since his time fulminate has continued to hold its place as the most satisfactory initiator of high explosions that has ever been found. In some European nations lead azide, PbN6, has recently been used to replace fulminate, but the use of azide has not found favor in this country.
Fulminate is also used extensively in mixture with other substances in primers for guns to initiate the ignition of the propelling charge. Other nations continue this use, but here the failure of ammunition so primed to function satisfactorily, caused the substitution of non-fulminate mixtures, and the one now in use has given much more satisfactory results.
Prior to the World War, production of fulminate in the United States was very small, as our high revenue tax on ethyl alcohol rendered the cost of manufacture almost prohibitive in competition with imported fulminate. In 1918 our production was increasing rapidly, as shown in Fig. 7.
For the manufacture of one pound of fulminate of mercury the following material is required: Mercury 0.77 pound; nitric acid (100 per cent), 4.42 pounds: ethyl alcohol, 5.88 pounds.
Materials Required in the Manufacture of all High Explosives
Nitration, whether of an aromatic compound or of cotton or glycerine, is always carried out with a mixture of sulphuric and nitric acids, and not with nitric acid alone, for even the strongest nitric acid does not act well by itself. One of the main function? of the sulphuric acid is to combine with the water formed during the reaction and prevent its diluting the nitric acid, but it appears probable that it also takes an active part in the reaction, and that to some extent at any rate, it combines first with the substance to be nitrated to form a sulphuric ester or sulphonic acid, and that it is this which is afterward acted upon by the nitric acid. That this two stage nitration is what probably takes place is shown in the nitration of phenol, for it has been found that with this material the best results are obtained by first acting on it with sulphuric acid with the formation of phenol sulphonic acid, and then as a second stage of the process to act upon the latter with nitric or mixed acids, when picric acid results.
In all nitration the use of sulphuric acid makes the nitration not only more complete, but also much more rapid.
In the process of nitration important amounts of acid are consumed. The quantities of acid previously stated as required in the manufacture of the various explosives are the average figures from our explosives plants in 1917 and 1918. The consumption of acids in the manufacture of explosives in most foreign countries is even higher, a French official estimate of their requirements being "sulphuric acid 4 to 5 times the weight of the explosive, nitric acid 2 to 3 times the weight of the explosive."
1. Sulphuric Acid.—Sulphuric acid is made from pyrites, zinc blende, or sulphur by the "chamber process" or the "contact process." In both of these processes the first stage is to burn the sulphur or sulphur-containing ore in an excess of air, converting the sulphur to sulphur dioxide. It is then necessary to make the sulphur dioxide combine with a further quantity of oxygen to form sulphur trioxide, which when combined with one molecule of water forms sulphuric acid.
In the chamber process the extra oxygen is added by mixing a small quantity of oxides of nitrogen, added in the form of spray or with a steam jet, with the sulphur dioxide.
In the contact process the sulphur dioxide and a considerable excess of oxygen are passed over a platinum catalyzer, which brings about the conversion to sulphur trioxide.
A disadvantage of the chamber process as a means of manufacturing sulphuric acid in time of war is the fact that it uses up considerable quantities of nitric acid, which can not well be spared from the supply available for nitration in the manufacture of explosives. In addition, the contact process is the one best adapted to the production of pure concentrated acid and oleum, as required for the manufacture of explosives. For this reason most of the large explosives plants now make their acid by the contact process.
Before the war a large part of the sulphuric acid manufactured in this country was made from pyrites imported from Spain. During the war the difficulties of transatlantic transportation greatly reduced these imports and our own resources were rapidly developed to take care of the market formerly supplied by Spain, as well as of the steadily increasing demand from the Allies and from our own industries. The principal increases in production were from the pyrites mines of Virginia and the sulphur deposits of Louisiana and Texas. The field in the latter two states, made workable through the ingenuity of an American engineer, now supplies the raw material used in the manufacture of most of the high grade acid made in this country. Our supplies of sulphur are much larger than those of any other nation, and our plant facilities have been increased until our possible production of the acid is now more than three times .what it was before the war.
The consumption of this acid in the industries other than the manufacture of explosives is very large. Even in 1918 when our production of explosives was at its maximum, less than one-fourth of the sulphuric acid made was used in explosives manufacture. At this time our national production of the acid was about 450,000 short tons per month (all strengths reduced to a basis of 100 per cent acid) and approximately 100,000 tons were used in the explosives industry.
Because of the consumption of sulphuric acid in the industries it has been stated that "the extent of a nation's civilization can be judged from the amount of sulphuric acid it manufactures." Certainly the industrial progress of a nation can be accurately judged in this way. Our tremendous production of sulphuric acid corresponds with our commanding position among the industrial nations of the world.
The increase in our manufacture in recent years and the result of the war demands for this acid, both from explosives plants and other industries, are shown in Fig. 8.
2. Nitric Acid.—If the industrial progress of a nation can be judged from the amount of sulphuric acid she produces, her ability to defend herself from her enemies can even more surely be judged from the amount of nitric acid she is capable of producing, for no satisfactory military explosive has ever been made, from the date of the first discovery of black powder down to the present time, that did not contain fixed nitrogen. Since practically all the nitric acid made in this country is made from sodium nitrate imported from Chili it is evident that here is an extremely grave source of national weakness.
The first form of fixed nitrogen used in the manufacture of explosives was potassium nitrate, also known as saltpetre. It is formed in the decomposition of animal and vegetable matter under favorable conditions. Deposits of saltpetre are formed in considerable quantities only in thickly populated countries which are sufficiently warm to accelerate the decomposition, and which have a long dry season during which the deposit can collect without being washed away. Of course these conditions are not found anywhere in the United States.
True saltpetre remained the chief source of fixed nitrogen until about 1850 when sodium nitrate (Chili saltpetre) began to take its place. The consumption of Chili saltpetre has steadily increased and to-day it is the only important source of nitric acid for the principal nations of the world except Germany.
Mention has previously been made of the development of synthetic methods for the fixation of atmospheric nitrogen by the Germans. This development was probably the most important accomplishment of Germany in preparation for the World War.
It has long been known that the nitrogen and oxygen of the air would combine in the intense heat of the electric arc, but the power requirements are so high that the manufacture of nitric acid by this process is usually not economically practicable except in countries like Norway and Iceland where large amounts of electric power can be obtained at very low cost. The arc process for the fixation of nitrogen has been developed on a large scale only in Norway.
Other methods for the fixation of atmospheric nitrogen have been developed, and two of these were used in Germany to supply her with the nitrates essential for her explosives and for her agriculture/ In the older of these processes, the cyanamide process, calcium carbide is first formed. This when heated in an atmosphere of nitrogen gas, secured from a liquid air apparatus, is converted into calcium cyanamide, CaCN2. The cyanamide when heated with steam in autoclaves is converted into calcium carbonate and ammonia. The latter can then be oxidized to nitric acid.
In the second process, the Haber process, nitrogen and hydrogen are made to combine directly to form ammonia by passing the mixed gases in the proper proportions over a catalyzer at high temperatures and pressures. The ammonia is then oxidized as in the cyanamide process.
Both of these processes have been developed on a very large scale in Germany, so that she is now in a position not only to supply her own needs, but also to sell a large surplus to other countries in competition with Chili saltpetre. If permitted, Germany will undoubtedly resort to her old methods of price cutting so as to prevent the development of synthetic nitrate manufacture in other countries where investigation of the subject is now under way.
In the United States more than one hundred million dollars was spent in the construction of nitrogen fixation plants during the war, but the processes have not yet been perfected on the large scale attempted. Since the armistice almost no advance has been made in the way of production, and progress is now practically at a standstill awaiting a decision from Congress as to the disposition to be made of the plants. In the meantime private capital hesitates to enter the field because of doubt as to the future of the government plants, and question of the ability to compete with imports of nitrates from the natural deposits in Chili and from the fixation plants already well established in Germany.
The seriousness of our dependence upon imports is evident from the fact that in 1918 we imported 60 per cent of all the sodium nitrate produced in Chili. Our 1919 explosives program would have required the consumption of 2,246,654 long tons of sodium nitrate or its equivalent, and this is only 600,000 tons less than the maximum annual production from the Chilean fields. Assuming that we could have obtained the amount we would have required from this source, it is apparent that the Allies, who are also dependent upon this source of supply would have been in desperate straits. Our own agricultural interests would also have suffered severely from the shortage of nitrates for use as fertilizers.
It is evident that it is necessary as a matter of national safety to establish the nitrogen fixation industry in this country so that in case of future need we will not be dependent upon imports of a material which is an absolute essential in the manufacture of explosives for our fighting forces, and of fertilizers which are essential if the people of this country are to be clothed and fed.
Another potential source of nitric acid is the by-product ammonia produced in our gas works and coking plants. The byproduct coke ovens now constructed have a working capacity of 179,320,000 pounds of ammonia annually. If all of this were to be oxidized to nitric acid, 382,564 short tons of acid would be produced. This is the equivalent of 535,590 long tons of sodium nitrate. Of course all the ammonia could not be spared for such conversion to nitric acid, because of the extensive use of ammonia in the essential industries, and in the manufacture of ammonium nitrate and ammonium picrate.
The rapid increase in the production of nitric acid in 1918 to supply the demand in the manufacture of explosives is shown in Fig. 9. In contrast with sulphuric acid, nitric acid is used in comparatively small amount in other industries. In 1918 more than 95 per cent of the total consumption was in the manufacture of explosives.
For the manufacture of one pound of 100 per cent nitric acid from sodium nitrate the following material is required: Sodium nitrate, 1.57 pounds; sulphuric acid (100 per cent), 1.46 pounds. Some manufacturers use much more nitrate than this, but the above figure represents the average result in efficiently operated American plants.
Other Materials Required for One or More of the Important High Explosives
1. Coal Distillation Products.—The coal distillation products used in the manufacture of most of the important high explosives are by-products in the manufacture of coke in by-product ovens, and of the manufacture of coal gas for city distribution. In both of these processes the essential chemical operation is to decompose certain special grades of bituminous coal by heating to a high temperature out of contact with air. The main products of the operation are coke and gas; the by-products are ammonia and coal tar. In the coal tar are the benzene, toluene, phenol, cresol, xylene, and other aromatic hydrocarbons used in the manufacture of explosives.
Since these substances are by-products, the quantity produced depends not primarily on the demand for them, but on the demand for coke and gas, particularly the former. As more than 80 per cent of all the coke produced in this country is used in blast furnaces in the manufacture of pig iron, it is very fortunate that under the conditions of modern warfare the iron and steel industry is working at maximum capacity, for the increased demand for pig iron naturally results in greater production of coke, and also of the by-products so essential for the manufacture of modern high explosives. In the late war, however, our recovery of by-products was not half what it could have been had other methods of coking been used in the plants equipped with beehive coke ovens. This type of oven wastes not only all of the valuable by-products, but also all of the gas.
The beehive oven, so-called from its shape, preceded the byproduct oven in the coke industry of this country by many years, and occupied a commanding position with a production of more than twelve million tons of coke per year when the first byproduct oven was built in 1893. The number of by-product ovens increased slowly, and it was not until 1912 that the by-product production of coke equaled that obtained from the beehive ovens in 1893. In the meantime the production of the latter had more than trebled.
Among the reasons for the beehive ovens retaining the lead in production were: the fact that it was first in the field; that large supplies of natural gas were available near the principal fields, making the manufacture of coal gas unprofitable; that the supply of coal was abundant and very cheap; and that the market for the by-products in this country was extremely limited.
Unlike the beehive ovens the by-product ovens were generally not built in the immediate vicinity of the coal mines, but rather were located in the vicinity of industrial works where a profitable market for the gas could be found.
With the gradual depletion of the supplies of natural gas, and the increased demand for the by-products, particularly when the Allies turned to this country for explosives, conditions changed even in the vicinity of the coal fields, and the construction of byproduct ovens in large numbers was energetically begun. The change to this type of oven has been so rapid that in 1919, for the first time in history, the output of coke from our by-product ovens was greater than that from the beehive type.
The growth of the two types of ovens in the coke industry, and the production of pig iron corresponding is shown in Fig. 10. It will be noted that the production of beehive coke varies the more markedly from year to year, and is the more sensitive to variations in our pig iron production. Although the beehive capacity is still the greater, the tendency is for the by-product ovens to work at nearly full capacity to carry the normal load, and for the beehive type to be called upon only for the "peak load." It seems but natural to suppose that future increase 1 of capacity, and necessary replacement of old ovens will be accomplished by the construction of more by-product ovens, and that in the not very distant future the beehive type will cease to be an important producer of coke in this country. Certainly this condition is to be hoped for, to prevent further waste of materials so necessary to our national safety.
(a) Benzene, Toluene, and Xylene.—In addition to the benzene, toluene, and xylene obtained from the fractional distillation of coal tar, important amounts of these substances are carried away with the gas. In 1914 only one company operating by-product ovens in this country had equipment to strip these products from the gas, but now, as a result of the war demands, all by-product plants and most city gas plants are so equipped, thus vastly increasing our national production.
The city gas plants do not produce as large an amount of byproducts in proportion in this country as in Europe, because of the extensive use of "water gas" here instead of coal gas. Important quantities of benzene, toluene, phenol, and other coal tar products were, however, obtained from our city gas plants during the war.
The supply of toluene from by-product ovens and gas plant was never sufficient to supply the demand for TNT, and consequently other possible sources of supply were diligently investigated.
The first and most important of the processes to obtain toluene from other sources than coal distillation was that developed by the General Petroleum Company of Los Angeles, California. In their process a yield of six per cent of toluene was secured from a distillate from certain California bituminous base petroleums, by subjecting this distillate to high temperature while under great pressure. Two plants were built to operate on this principle. Their combined rated capacity was 3,000,000 pounds of toluene monthly.
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Two other cracking processes, one known as the "Rittman" process and the other known as the "Hall" process, were investigated and production of toluene from solvent naphtha was conducted on a small scale by each of these processes while hostilities lasted.
With the present low price of toluene it is extremely doubtful that it i would be profitable to make it by any of these cracking processes, but the methods are now available as a means of increasing our supply if the need ever again arises.
The great increase in our production of benzene and toluene from all sources is shown in Fig. II. This increase was brought about mostly by the rapid increase in the number of our by-product ovens and the installation of apparatus for the scrubbing of gas. The maximum possible recovery of xylene has never been made, because this material was not used in the manufacture of explosives until the closing days of the war. It is estimated that we can count on a production of xylene about one-fifth as great as that of toluene.
(b) Phenol.—The coal tar acids, phenol and cresol, are present in much larger amounts in the tar from coal gas works than in that from by-product ovens or water gas plants. In Europe, and especially in England, a much larger proportion of coal gas tar is available than in the United States, because of the lesser use of water gas there in illuminating gas plants. This accounts for the fact that natural phenol to the extent of about 8,000,000 pounds annually was regularly imported from Europe before the war. As has been previously mentioned, the cutting off of our imports combined with the great demand for picric acid caused the rapid development of synthetic manufacture of phenol from benzene. Our production of phenol from coal tar also naturally increased with the expansion of the by-product industry, but during the war by far the largest part of our phenol was made synthetically. Our production of phenol in 1918 is shown graphically in Fig. 12.
(c) Ammonia.—The distillation of coal is now the only important source of ammonia. Naturally the expansion of the byproduct coking industry in recent years resulted in greatly increased production of ammonia. Our rapidly rising production of ammonia in 1918 is shown in Fig. 13.
(d) Commercial Uses for the Coal Distillation By-Products.—It is evident that these so-called coal tar products will not be available in sufficient quantities to satisfy our needs for explosives in case of future war unless the demand for them in time of peace is sufficiently great to make it profitable to operate plants for their recovery. It is therefore profitable to survey the uses to which they are now put. The first class of compounds that generally occurs to the mind in connection with coal tar products is dyes. The close relation between dyes, explosives, and poison gases is of the greatest importance from the military point of view, because the dye factory can be quickly converted into an explosive or poison gas factory in an emergency, using the same staff, materials, and apparatus, with only slight modifications which are easily and quickly made.
The relation between picric acid and sulphur black, the dye ranking first in point of quantity production in this country, is particularly intimate, the manufacture of these two products from benzene being identical until the last step. It is evident that a plant making sulphur black in peace times can quickly get into production of picric acid in case of emergency. The plant has the entire process, with the exception of the last step, in actual operation, and the chemicals for this last step are ready at hand. The equipment needed for the final process can also be kept at hand with a comparatively small outlay of capital. Additions to the plant may be made with maximum speed, as all the technical problems and details of design of the apparatus must necessarily have been worked out in advance, and therefore no time need be lost in experimenting or in making plans. Moreover such a plant will already have an experienced staff capable of quickly absorbing and training additional workers for operating a much larger plant.
A relation similar to that discussed above, although not so close, exists between TNT and the various dyes derived from toluene. The relation is, however, close enough to be of gTeat military importance. These as well as other nitro-aromatic compounds in military use as high explosives can be speedily produced in large amounts by a nation with a well developed dye industry, but only with much more difficulty and considerable loss of time by a nation without a dye industry. The propellant, fulminate, and dynamite branches of the explosives industry do not have as close a relationship to the dye industry as does that branch dealing with the nitro-aromatic compounds.
It is well known that these military considerations have received great weight in the development of the German dye industry and that the relatively small amount of equipment required for the conversion of their dye factories into explosives plants was ready at hand.
In the United States to-day certain chemical plants which were erected during the war to manufacture explosives and poison gases have already been converted into dye or intermediate plants, or to other peace-time purposes. This procedure in America is a complete reversal of the procedure in Germany at the outbreak of the war.
Another important point to be considered in connection with the relationship of the dye industry of a nation to her potential production of high explosives is the fact that the dye industry encourages the researches of a large number of skilled organic chemists with the resultant knowledge of organic compounds that is of invaluable assistance in the wartime development of the explosives industry.
Other important uses for coal tar products are the manufacture of synthetic drugs, tanning materials, artificial flavors and perfumes, photographic chemicals, and phenolic resins. The development of these industries is a distinct military asset, both because the chemical processes and plants can be readily adapted to the production of explosives, and because a commercial demand for the raw materials in time of peace encourages the installation of by-product ovens which will insure an ample supply of the raw materials required for explosives in time of war.
The present production of benzene and toluene is so great that the price has fallen to about twenty-four cents per gallon for the former and twenty-six cents for the latter. At these prices they are finding extensive use as fuels for internal combustion engines being substituted either in whole or in part for gasoline.
Both of these materials are also being extensively used as substitutes for turpentine as a thinner for paints and varnish. They are also used as a paint remover, as solvents for many organic substances, particularly rubber, and as raw material in the manufacture of certain varieties of artificial leather.
The uses of ammonia in industry are many and varied. The greater part of our production in times of peace is used in the manufacture of fertilizers, and in the refrigeration and chemical industries.
The high boiling fractions of coal tar distillation, not suited to the manufacture of explosives, find extensive use as wood preservatives, road surfacing materials, and in the manufacture of roofing materials. The pitch left behind after the distillation of the tar is a very pure grade of carbon, and as such is extensively used in the manufacture of electrodes.
These many and varied uses of the materials recovered in the by-product ovens seem to insure the continued increase of this type of oven in the future.
2. Cotton.—In 1918 almost twenty per cent of our total crop of cotton was nitrated in our explosives plants, but less than one twenty-fifth of this went into the manufacture of guncotton, the remainder being used in the manufacture of smokeless powder. In view of the decreasing importance of guncotton as a military high explosive there seems to be no reason to fear that our supply of cotton for the manufacture of this material will ever be inadequate.
3. Mercury.—In spite of the rapidly increasing production of fulminate, the total amount of mercury consumed in its manufacture is but a small part of our national production. In 1918 more than 36,000 tons of mercury was produced in the United States and only 390 tons were used in fulminate manufacture.
4. Ethyl Alcohol.—Ethyl or grain alcohol is obtained principally by the distillation and rectification of the product of fermentation of fruit juices, molasses, and the sugar produced by the action of the diastase in malt upon the starch in grains and vegetables.
Our distilleries can easily be adapted to the production of high proof alcohol, and fortunately the eighteenth amendment to the Constitution does not prohibit the manufacture of alcohol for other than beverage purposes. The manufacture of grain alcohol is, however, so heavily taxed, and the requirements of our laws so exacting, that the price to the consumer is greatly increased.
As the consumption of alcohol in industry is increasing in spite of the restrictions upon its sale and use, production is increasing to keep pace with the demand. Since there is every reason to expect a continuing increase in consumption and production, particularly in view of the fact that alcohol may some day compete with gasoline as a motor fuel, we may confidently count upon a supply of alcohol sufficient to satisfy our needs in the manufacture of high explosives. The quantity required for this purpose is insignificant in comparison with the amount used in the manufacture of our smokeless powder.
5. Methyl Alcohol.—Methyl or wood alcohol is obtained by the dry distillation of wood. Our forest resources are still so great that there is no apparent danger of a lack of the small amount of wood alcohol used in the manufacture of high explosives. However, when one considers the many uses of our forest products, such as the varied uses of paper and of articles made from paper pulp; the wide variety of materials known under the general classification of " naval stores " ; and the multitudinous uses of lumber in our industries, he is at once impressed with the fact that the rapid destruction of our forests is a national calamity, and that prompt steps toward reforestation are essential to our future prosperity.
6. Starch.—This nation is one of the largest producers of starch-containing cereals and vegetables and should consequently have no fear of lacking the relatively small amount of starch required in the manufacture, of nitro-starch explosives. It is true that only certain varieties of starch have been successfully nitrated, and that special methods of purification are necessary, but the experience of the late war demonstrated that plants for the production of the starch desired could be erected and put into operation with sufficient rapidity to insure an ample supply for the nitro-starch factories.
7. Chlorine.—Chlorine gas was used by us in large quantities during the World War in the manufacture of picric acid from benzene. Most of our chlorine comes from plants engaged in the manufacture of soda by the electrolytic process. The chlorine gas which was formerly a most objectionable waste product is now used in the manufacture of bleaching powder. Fortunately the volume of business done by this industry is so great that ample supplies of chlorine are available for the manufacture of explosives in time of war.
8. Soda.—The specifications under which practically all of our explosives are manufactured require them when delivered to be free from all trace of the acids used in their manufacture. Usually a small amount of sodium carbonate or bicarbonate is dissolved in one of the washing waters to neutralize any acid that might still be present. The amount of soda required for this purpose, even when our production of explosives was at the maximum during the war was negligible when compared with our monthly production, which averaged more than 300,000,000 pounds.
Summary
In the production of high explosives, as in almost every other branch of war activities, America "made good" in a manner exceeding even the fondest hopes of her friends. At the time of the signing of the armistice our production of military high explosives was at a rate forty per cent greater than that of Great Britain and almost double that of France. Our total production in 1918 is shown in Fig. 14.
The results achieved after we became a belligerent cannot, however, be taken as representing what we could have accomplished in a similar time with the explosives industry of the country in a normal condition, for our production of explosives had greatly expanded before we entered the war.
The huge plants which rendered possible our war production of explosives have now largely been dismantled or converted to other uses, so that we would not be able to resume production at the rate possible at the time of the armistice without a considerable interval for preparation. Nevertheless, the development of our resources of raw materials, the perfection of manufacturing processes, and the experience gained in actual quantity production are real national assets which will be invaluable in case of future need.
At the cessation of hostilities our production of high explosives was still increasing rapidly, and there is no cause to doubt that if allowed sufficient time we can produce much larger quantities of military explosives than any other nation in the world.
Our entire production of explosives is, however, dependent upon imports of nitrate from Chili, and hence may be greatly reduced or even brought to a halt by the operations of an active naval force, even though the latter be inferior in strength to our main fleet. This deplorable dependence upon imports for materials required in the manufacture of our explosives can be eliminated by the establishment of plants for the fixation of atmospheric nitrogen, and no efforts should be spared to insure the prompt establishment of this industry in this country.
Every encouragement should also be given our struggling dye industry, both because of the ready adaptation of dye processes and plants to the rapid production of explosives in the event of war, and because the dye industry in time of peace encourages increased production of the materials required in the manufacture of explosives in time of war.
If dye manufacture be encouraged, the use of by-product ovens in the manufacture of coke be increased, and the nitrogen fixation industry be established on a scale corresponding to our natural wealth of the other materials required in explosives manufacture, America need have no fear that, in case of aggression by a foreign power, her army and navy will ever be handicapped by any lack of high explosives.