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fitting. The size of the sample obtained is dependent approximately on the relation between the width of the slot and the total weir circumference. Actually, the sample will be smaller than indicated by this proportion, on account of the fact that the sides of the slot restrict the flow sbmewhat. The depth of flow is the same, however, for the slot and for the balance of the circumference. A 10-in. in diameter weir with a 0.25-in. slot in a 1-in. wide plate will give a sample of about one one-hundred and twentieth of the total liquid flowing; or with an 0.125-in. slot, one two-hundred and fortieth.
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Fig. 2 illustrates the relation between the width of the sample slot and the total weir. A funnel constructed of light sheet metal and soldered to both sides of the slot plate serves to carry off the sample. If the volume of liquid is very large, it may be necessary to reduce it twice, as in Fig. 3. I n a mill grinding 2000 tons of cane per day, the juice may thus be reduced to a bucket sample per 6-hr. shift. Drainage cocks are indicated to empty the pipe lines a t shutdowns. The sampler can be made up of standard pipe fittings in any mill shop.
ADDRESSES AND CONTRIBUTED ARTICLES Incendiaries in Modern VVarfare’~2*3 By Arthur B. Ray UNIONCARBIDEA N D CARBON RESFARCH LABORATORIES, INC.,LONGISLAND CITY, N. Y.
The destructive action brought about by the natural elements-fire, air, and water-may be looked upon as infinite when compared with the damage which can be caused by other means in a brief period of time. In harnessing one of these natural elements-fire-and applying it as a war weapon, we have assurance of its efficacy in the universal dread in which i t is held as the most ruthless enemy of mankind. The idea of using incendiaries in warfare is not modern: in fact, the use of fire as a destructive weapon dates back to early Biblical times, when burning oils and ignited fire balls consisting of resin and straw were thrown both by the defenders and attackers of fortified towns. In later times crude iron latticework bombs up to 2 f t . in diameter, filled with highly flammable materials, were ignited and projected by catapults or thrown from fortifications. The iron skeleton of such a medieval bomb may be seen in the Tower of London. But, while, from the earliest times, fire has been considered to be of possible military value, means for scientifically using i t as a powerful weapon were not developed until the recent war. The effectiveness of incendiary armament is dependent upon the character of the incendiary materials employed and upon the devices by means of which the materials are carried to the target and set in action there. The development of this type of armament, therefore, involves both chemical and mechanical investigative work which must be done in close cooperation with those who are fully conversant with the military requirements and limitations. I shall endeavor in this paper to point out the general characteristics of all the typical materials and devices developed by the warring nations and to discuss, in their proper place and in somewhat greater detail, the more important developments with which we were intimately connected in the United States. The materials and devices will be discussed separately in so far as it is possible to do so. P A R T I-INCENDIARY
MATERIALS
Since the many devices differ widely as to action, it is obvious Presented before the Division of Industrial Chemists and Chemical Engineers a t the 58th Meeting of the American Chemical Society, Philadelphia, Pa., September 2 to 6, 1919. 2 This articIe is published by permission of the Chief of the Chemical Warfare Service. 8 Very soon after our entrance into the war the development ofincendiary armament was begun in this country by the Bureau of Mines and continued by the Chemical Warfare Service in cooperation with the Ordnance Department. Investigations concerning all the desired forms of armament, except incendiary small arms ammunition which was developed a t Frankford Arsenal, were carried out at the American University Experiment Station b y the Incendiary Section, under the direction of Capt. Arthur B. Ray, C.W. S., and by the Pyrotechnic Section, under the direction of Major G . A. Richter, C. W.S.,with the invaluable assistance of the Ordnance Department. 1
that no one incendiary material can be used. In fact, for practically every device a special material has been developed to give the desired result as to time of burning, kind of flame, kind of reaction products, etc. For convenience of discussion, we may classify all the incendiary materials as follows: White phosphorus, thermite, oxidizing agent-combustible mixtures, flammable materials used as such, the special material called “solid oil,” and spontaneously flammable liquids. PHOSPHORUS On account of its property of igniting spontaneously when exposed to air, white phosphorus was early suggested as an incendiary material, and a number of devices, such as bullets, bombs, shells, and grenades, which depend upon it for incendiary effect, have been developed and used. Against substances which can be ignited by a momentary exposure to a small flame, phosphorus undoubtedly is of value, but for setting fire t o materials which are relatively difficult to ignite, phosphorus is of very little value, because of its low temperature of burning and because the phosphoric oxides formed act as an excellent fireproofing material. Bullets containing phosphorus have proved to be very eff ective against hydrogen-filled aircraft and against airplanes when the gasoline tank is punctured. The phosphorus pellets which these bullets carry are cast or cut from rods and are coated with aluminium dust-the aluminium acting both as a preservative while handling and as an intensifier of the flame when the bullet functions. The bullets are so designed, as will be shown later, that when fusible plugs in the side are melted by the heat of friction, the phosphorus is exuded and burned. The path of the bullet may be followed by the trail of smoke. Grenades and 4-inch Stokes’ mortar bombs containing phosphorus were effectively used against personnel, particularly when exploded in dug-outs. The inconvenience caused by the obnoxious smoke and scattered burning particles of phosphorus was considerable.
THERMITE The well-known properties of the aluminium-iron oxide mixture called thermite caused it to be widely used, in various modified forms, as an incendiary material. Such mixtures have the advantage that when ignited they produce an enormous amount of heat very quickly and that the molten metal and slag resulting from the reaction will penetrate metal and prolong the incendiary action upon flammable materials. These mixtures when used alone, however, have the disadvantage that the incendiary action against, say, wood structures is confined to a very small area, and that a very large percentage of the heat energy set free is wasted because it is set free too rapidly to be utilized effectively, except by very flammable material. Since
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such material is not often present as the target, the method of placing it with the thermite in the incendiary device was early adopted. As the primary incendiary material-that which is first ignited and which starts the conflagration-it is believed that thermite is by far the most effective material used. The secondary incendiary material-that which is ignited by the thermite reaction and which continues the conflagration-may be a flammable liquid as such or absorbed in some carrier, or a specially prepared material which will burn for a long time with a large flame and effectively set fire t o a difficultly ignitable target. The most satisfactory secondary material is not only capable of burning with a large hot flame, but actually renders the target flammable. Such a material is the solid oil developed byus, which will be discussed later. So, by using thermite in the manner described, the large amount of heat energy suddenly set free is, to a large extent, utilized, and causes the secondary incendiary material t o begin its action with a tremendous burst of flame which is most effective. coMPosITroN-The general military requirements of a thermite mixture are that i t be inexpensively prepared in sufficient quantities, that i t function properly under all conditions of military use, and that the reaction produce the desired effects. Since it makes no difference what the reaction products are so long as they give the desired incendiary effect, i t is obvious that there are possibilities of varying the composition of the mixture greatly. Through the kindness of Mr. Deffler of the Goldschmidt Thermite Co., a number of mixtures in which copper, nickel, manganese, and lead oxides replaced the iron oxides were tested at the company's plant. Also thermite whose constituents were in smaller particles (through 50 mesh) than usual was tested. The results showed that, for our purpose, the incendiary effect of the ordinary thermite was as good or better than could be obtained with the special mixtures. Manganese dioxide was present in mixtures used by the Germans in certain early incendiary bombs. One particular mixture contained Manganese dioxide Mngnetic iron oxide Aluminium Magnesium CaO
Iasolubles Resin (by difference)
Per cent 22.00 38.66 16.34 8.45 1.14 4.24 9.19
The aluminium and magnesium were present in the form of a n alloy of the approximate composition A1 : Mg = 66 : 34. A mixture of iron oxide, copper oxide, and aluminium was also used. Thermite mixtures in which were incorporated oxidizing agents other than those necessary for the thermite reaction were investigated but, for our purposes, none were found to possess special merit. It was suggested that sodium nitrate present in large pieces would be melted by the thermite reaction and that the molten nitrate would act as a powerful oxidizing agent and so increase the incendiary action upon the target. After a series of tests, however, it was concluded that the space occupied by the nitrate might better be occupied by thermite. A flaming thermite mixture which contained barium nitrate in addition to the usual consthents was developed and used by the British in their small drop bombs. It was concluded after many tests that a simple mixture of magnetic iron oxide and aluminium was the most satisfactory, taking all things into consideration, for general military uses. The specifications drawn up for this material state that the mixture shall contain 76 parts by weight of magnetic iron oxides and 24 parts of aluminium. There are, of course, limits to size of particles, purity of materials, presence of foreign substances, moisture, etc. BINDERS-since the loose thermite mixture is composed of
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two substances of quite different densities, i t may be rendered nonignitable by vibration, jars, or shocks, because segregation takes place under these conditions. This fact causes it, in the loose form, to be entirely unsuitable for military uses. To obviate this. difficulty, the mixture may be compressed or bound into a hard mass by such substances as water glass, sulfur, celluloid, etc. Preventing segregation by compression is quite possible, as investigations by the British and ourselves have shown. A series of compression tests a t various pressures showed that, a t a pressure of 12,000 lbs. per sq. in., the density of the ordinary mixture is doubled and the compressed block holds together very well. But, as the density is increased, ignition becomes more difficult, the propagation of the reaction uncertain, and the time of burning longer. I n actual tests in drop bombs, the compressed thermite was not considered t o give a much better incendiary effect than the same volume of thermite bound together with sodium silicate. The cost of obtaining a given incendiary effect with compressed thermite is, therefore, greater. On account of these facts, the British and ourselves did not recommend compressed thermite for general military use. However, the special flaming thermite which contains barium nitrate is used in the compressed form by the British. The use of sodium silicate as a binder for the thermite mixture was of course early suggested, since thermite so bound is used in the steel industries. The optimum amount of silicate to use for our purpose was determined by a series of experiments. It was found that the most desirable properties of ignition, propagation of reaction, time of burning, and incendiary action were obtained with thermite bound with 15 per cent by weight of 40' BC. sodium silicate. The thermite is simply mixed with the sirupy water glass, molded, and baked until dry. The baking operation must be carried out with some care to prevent accidental ignition and t o be sure that all the water is driven out. Sodium or potassium silicate was generally used by the other warring nations as a thermite binder. Besides preventing segregation, the silicate binder produces the marked advantage that the blocks react completely, whatever be the position of the point of ignition. The bound material is insensible to shock and shot, which permits its utilization in projectiles of high initial velocity and in offensive devices used by aircraft. Sulfur seemed to possess certain advantages as a binder, because i t combines with the iron formed to give further evolution of heat. Theoretically, a unit weight of a mixture made UP according to the equation 8-41 3FerOd 9s = 4AlzOa QFeS evolves practically the same amount of heat as the same weight of thermite containing no sulfur but, whereas ordinary thermite contains 24 per cent aluminium, the sulfur mixture contains only 18 per cent. Aluminium is the expensive constituent and this saving of 25 per cent is worth while, provided the mixture has satisfactory properties. But i t has one great drawbackwhen confined i t reacts with explosive violence and even when unconfined i t burns very rapidly and spatters as small drops, thus lessening the intensive incendiary effect. The pool of molten products from the reaction of ordinary or silicate-bound thermite is most effective in penetrating metal and prolonging incendiary action upon flammable materials. Tests of sulfurbound thermite did not show i t to be as satisfactory for our purposes as the silicate-bound material. It was used, however, by the French in an airplane drop bomb, and its explosive property was utilized to scatter the other ignited iscendiary materials contained in the bomb. Various organic materials such as resin, paraffin, and hard pitch, were investigated as possible binders, without satisfactory results. Celluloid as a binder proved to be fairly satisfactory, particularly where i t was desired to get a long flame and uniform burning of the thermite. Thermi'te bound with 4 per cent cellu-
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loid dissolved in ‘a suitable solvent was recommended by us for use in incendiary grenades. IGNITERS-For the ignition of thermite used in grenades, bombs, and certain projectiles where it is not desired to scatter the reaction products, an igniter, which has no explosive action, must be used. The commercial igniter, which consists of finely divided aluminium and barium peroxide mixed with a certain amount of coarser aluminium and black iron oxide, is satisfactory in this respect, but when loose i t deteriorates upon exposure to moisture or when jarred,and then often fails t o ignite. It is also readily ignited by passage of a rifle bullet through it. The segregation troubles seemed to be the most serious, however. A large number of mixtures were experimented with in an attempt to find a more suitable igniter, but without entire success. When it is pointed out that an igniter was desired which was stable and not affected by moisture or jarring, which did not react with explosive violence, which was itself ignited by the usual means employed in military practice, which, by its reaction, heated the thermite hot enough (to approximately 1800’ C.) to start its reaction, which was not ignited by firing a rifle bullet through it, and which could be inexpensively prepared in sufficient quantities, the failure to develop a perfectly satisfactory igniter is understood. No oxidizing agent which would not react explosively was found better than barium peroxide. Attempts to prevent segregation and moisture attack in the commercial igniter by the use of such binders as shellac and celluloid did not prove successful. So i t was concluded that the most satisfactory solution of the igniter problem was to protect the commercial igniter carefully from moisture before using and t o prevent segregation by slightly compressing i t into a suitable container which was then inserted into a hole in the thermite. This method was used with quite satisfactory results. The igniter can be ignited by a black powder flash, but i t is more satisfactory to use a “booster” charge, composed of reduced iron and potassium nitrate pressed on top of it. Such a booster mixture is readily ignited by the flash from a Bickford fuse. For the ignition of thermite in those projectiles where it is desired to scatter the molten products of the thermite reaction, giving a shrapnel effect, an entirely different sort of igniter must be used. An igniter for this purpose should possess all the safety characteristics of the other type, but should react SO rapidly and with such explosive violence as to ignite the thermite and scatter the reaction products. There must be a slight lag between the ignition and explosion, otherwise the unignited thermite will be scattered. The British were successful in developing a satisfactory igniter of this type, called “ophorite,” which consists of intimately mixed magnesium powder and potassium perchlorate. Both the British and ourselves attempted to develop a better or a cheaper explosive igniter, without success. Alloys composed of varying percentages of aluminium and magnesium are brittle, and consequently can be readily pulverized. Mixtures of these powders and potassium perchlorate are equal in power to the magnesium mixture, cost less, and have a greater density, but are distinctly more sensitive, and so could not be recommended. Ophorite is much easier to ignite than the commercial igniter and can be readily ignited by a Bickford fuse. Besides its use as a thermite igniter, it was also extensively used as an explosive in gas shell. Thermite in various modified forms was without question the most generally used and probably the most important incendiary material, but to be most effective it is necessary, as has been pointed out, to use it in conjunction with other flammable materials. Grenades, shell, trench mortar projectiles. and drop bombs containing thermite as one of their essential constituents have been used with marked success. OXIDIZIXG AGENT-COMBUSTIBLE MIXTURES Certain mixtures of what we shall designate the oxidizing
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agent-combustible type have been used with moderate success
in drop bombs and other special devices, but the most important use of such mixtures has been in small arms ammunition and in shell of small caliber where only a very small amount of special materials can be used and where an exact control of the time and character of action is necessary. It is with this type of mixtures that the essential surety of action and nicety of adjustment can best be obtained. Also for use in small unit drop bombs which are intended to ignite readily combustible targets, the advantages of a single mixture which can be relied upon to function properly are evident. It is quite obvious that devices as different as drop bombs and bullets will require very different types of mixtures for most effective action. The type of mixture desired for drop bombs must, broadly speaking, react to give considerable heat and flame when the bomb lands. There are no exact requirements of weight and no nice adjustment of time of reaction necessary. On the other hand, a mixture which is satisfactory for use in bullets and small shell must fulfil very rigid requirements as to weight per unit volume, time of reaction, character of reaction products and consequent change of weight during the reaction, and finally, character of reaction or incendiary effect. The ballistic requirements are even more important than the incendiary requirements, because the projectiles must be capable of accurate firing to have any effect. The projectiles must have a certain weight and position of center of gravity which must not be greatly changed during flight. By careful arrangement of the metal parts of the projectile or by employing in the mixtures compounds containing elements of high atomic weight, such as lead and barium, the weight requirement can be obtained. By using such a combination of combustible and oxidizing agent as aluminium and lead oxide, for instance, the reaction merely causes a transfer of oxygen, and the volume and weight of the mass are not greatly affected. So the projectile may be capable of incendiary effect during flight and still not be seriously affected ballistically. The duration of the reaction is also very important in those projectiles which act as incendiaries during flight. It should preferably start a short distance from the muzzle of the gun and continue during the effective range OF the projectile. The problem of adjustment of time of reaction may be solved by the judicious use of organic substances, which slow down the reaction, or by adjusting the ratio of combustible to oxidizing agent. The usual oxidizing agents employed in this type of mixtures are the nitrates of potassium and barium, the oxides of barium and lead, and the perchlorate of potassium. Chlorates are used in some cases. The usual combustibles include various finely divided metals, such as aluminium, magnesium, and iron; arsenic and antimony sulfides; sulfur; carbon; and a great variety of organic materials, such as shellac, resin, pitch, paraffin, charred linseed oil, gums, etc. Nitrated organic compounds mixed with combustibles have been used in some devices. Mixtures of inorganic oxidizing agents and heavy oils are effective only when the temperature produced by the combustion of the oil is sufficient to cause the decomposition of the oxidizing agent. It is, of course, important that these mixtures shall not segregate, and this is prevented either by compression, or by mixing with some substance which acts as a binder, and then heating or compressing. In certain mixtures the magnesium powder is coated with the binding material before mixing with the oxidizing agent. The common binding materials used are sulfur and the organic materials named above. Besides acting to prevent segregation, most of the binding materials cause the mixtures to be less sensitive and the action to be slower. For this reason they are usually spoken of as deterrents. The particular kind of binding material must be chosen with great care because it is a very important component of the mixture. Very nearly all of the mixtures which have been used with
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success in small arms ammunition and in small shell for securing tracing and incendiary effects contain magnesium or aluminium -preferably magnesium-for the reason that these metals can be readily oxidized to give an intense heat and brilliant light. The oxidizing agents employed with these metals may be the oxides of barium, lead. or strontium; the nitrates of barium, potassium or strontium; or the perchlorate of potassium. Potassium and barium chlorates have also been used in certain cases. A mixture of 17 parts barium peroxide and 2 parts of magnesium powder mixed with alcohol and compressed in bullets under a dead weight of around 2500 lbs. has given very satisfactory results. It is ignited very easily by the propellant alone and burns with a very hot, white flame. A mixture of 9 parts red lead and 1 part magnesium or 15 parts red lead and 1 part aluminium compressed into small shell under a pressure of around 15 tons per sq. in. was also used with great success. This mixture must be ignited by a primer, which may consist of 65 parts of potassium nitrate, 13.5 parts of sulfur, 19 parts of powdered antimony, and 2.5 parts of powdered shellac. A typical mixture containing the other type of oxidizing agent consists of 64 parts of barium nitrate, 28 parts of magnesium, and 8 parts of linseed oil. The linseed oil may be boiled or charred, and it acts as a binder and deterrent. Other materials, such as carnauba wax, shellac, and paraffin, have been used for the same purpose. This type of mixture must be ignited by a primer such as the magnesium-red lead mixture previously described. Bullets and some shells containing this mixture have been successfully used. It should be pointed out that when the mixtures just described are ignited a t or near the muzzle and react during flight, the path of the bullet or shell can be traced. Sometimes the tracing effect is of more importance than the incendiary effect. Mixtures which burn with a white light are good tracers a t night, but for day tracing a phosphorus filling which emits a smoke trail or a mixture which burns with a red light is preferable. Strontium salts are for this reason used in some mixtures in conjunction with magnesium or aluminium, a deterrent, and sometimes potassium nitrate or barium peroxide. Strontium nitrate, oxalate, peroxide, and carbonate have all been used. A primer is needed to ignite such mixtures. Specific mixtures used in small arms ammunition and shell will be discussed further when the devices themselves are described. As previously stated, a less important use of the oxidizing agent-combustible type of mixture is in drop bombs and other relatively large devices. Such mixtures were used early in the war, both in larger shell, which were intended to have an incendiary action on impact, and in various drop bombs, but in many cases were later discarded for modified thermite. The Germans made considerable use of this type of mixture, as well as the thermite type, as the primary incendiary material whose chief function was to ignite the other materials in drop bombs. A mixture which may also come under this heading, consisting of 20 parts paraffin and 80 parts of potassium perchlorate, was often used in conjunction with the igniting mixtures. For use in a small unit drop bomb developed by us which carried only a small amount of material and which was designed to set fire to very flammable targets, a mixture was desired which would give a large hot flame on ignition, burn for several minutes, and leave no protecting residue. A large number of mixtures were prepared and tested as to fitness for this particular purpose. I t was found that, of the oxidizing agents available, the chlorates gave best results. Perchlorates were eliminated because, unfortunately, they were not commercially available. The chlorate mixtures burned uniformly with a large flame and with a time factor that could be controlled. Where an oily substance was used as a binder or filler, they passed all the safety tests. Aluminium was found to be the most desirable combus-
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tible in conjunction with a binder such as rosin, boiled linseed oil, or asphaltum varnish. In making comparative tests of the various mixtures a dart filled with the mixture was burned in a standard wooden box open a t one end and side only. The effect on the box, the time of burning, the length of the flame, the character of ash, and the weight of material were all taken into consideration in judging the mixture. Such mixtures as looked promising were then put through the surveillance and safety tests. The tendency to segregate, ability to stand a moist atmosphere or a temperature of 140' F. for a week, and sensitivity t o sudden shock, t o friction, and to vibration were determined. The few mixtures which survived these tests were next tested on a large scale in darts, and the availability of components, cost, safety and ease of manufacture, and the actual incendiary effect were considered. The mixture finally recommended consisted of 54 parts barium chlorate, 16 parts rosin, 14 parts aluminium, and 16 parts asphaltum varnish. The primer recommended for use in igniting this mixture consisted of reduced iron and potassium permanganate, bound with paraffin. This primer was found to be the most satisfactory, after a large number of tests, as to actionand deterioration. One of the mixtures tested during this investigation and found unsatisfactory consisted of 1 part hexamethylenetetramine and 2 parts sodium peroxide. This mixture attracted considerable attention because of the fact that a Dr. Scheele, taken into custody by the Department of Justice, claimed that i t had been used in attempting the destruction of the cargoes of thirtyfive vessels. Our experiments with this mixture showed t h a t i t has no great affinity for moisture, can be handled without risk in any sort of metal container, and that when ignited by means of sulfuric acid or flash from a Bickford fuse itreacts very rapidly in the open with great evolution of heat and a large flame, but that if confined it reacts explosively. A lead container is ideal for the mixture. The addition of a small amount of heavy oil or talc caused the mixture to burn longer,and reduced the sensitiveness. The British also experimented with this sort of mixture and found that sodium benzenesulfonate could be successfully used in place of che hexamethylenetetramine. For use in certain small drop bombs a modified form of this peculiar mixture has possibilities. After many large-scale tests it was concluded that it is not a satisfactory material for use in the larger incendiary devices. Dr. Scheele's extraordinary claims for the mixture were never substantiated.
FLAMMABLE MATERIALS USED AS SUCH The flammable materials used as such without any particular treatment or admixture of oxidizing agents, etc., include phosphorus (previously discussed), resins, pitch, sodium, celluloid, and the various sorts of flammable liquids and oils. Certain of these substances were used as the secondary incendiary material in projectiles and drop bombs, but the most important are the oils and liquids used in flame projectors. Almost any liquid which will burn will, of course, have some incendiary effect, but a liquid which will satisfy all the military requirements and give the maximum incendiary effect in any particular device can be developed only by a critical study of both physical and chemical properties, and after many tests. While the actual heat of combustion of a liquid is a determining factor, it is not the deciding factor in causing it to be rejected or accepted for incendiary purposes. The fact that it vaporizes too readily, has a fire point which is too high, or leaves a fireproofing residue on burning may cause a liquid with an exceptionally high heat of combustion to be rejected. The manner in which it is to be used or ignited determines the desired properties. A liquid which must be ignited by an explosion of black powder, as in certain types of drop bombs and projectiles, or by momentarily coming in contact with a small flame, as in flame
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projectors, must contain a definite minimum percentage of a constituent with a very low fire point, such as carbon disulfide, gasoline, or benzene; but a liquid which has a relatively high fire point may be satisfactorily used in conjunction with primary incendiary materials which react with a large evolution of heat. The chief requirements of a liquid mixture for use in flame projectors are that it must be readily and easily ignited, must not have too low a specific gravity, since a light mixture tends to spray a t the nozzle of the projector and so decrease the range, and must be of such a character that combustion does not occur needlessly during the passage of the stream through the air or, to any large extent, until the stream has reached its objective. I n other words, the desired object is attained when the ignited liquid is thrown upon the target some distance away. It is not desired merely to project a flame. With these considerations in mind, an extended investigation of liquid mixtures for use in the American flame projectors was carried out. Mixtures of various liquids, such as gasoline, kerosene, carbon disulfide, turpentine, benzene, water-gas tar, petroleum distillate, fuel oils, gas oils, and others, were tried out. It was early found that the heavier mixtures, provided they are not too viscous or too volatile, give a better trajectory, that is, tend to spray less and are thrown farther than the light mixtures. The heavy liquids also burn farther away from the nozzle, which is very desirable for the operator’s comfort, are more resistant to wind pressure, and carry sufficient unburned material t o saturate and render the target highly flammable. The most satisfactory mixture, therefore, consists of a heavy, rather viscous oil or tar and a more fluid and more flammable liquid. For the heavy viscous liquid, water-gas tar (sp. gr. 1.044and flash point 122”) was found to be most satisfactory from all standpoints. Mexican fuel oil was also found to be very good. For the light flammable liquid, benzene heads (sp. gr. 0.756 and flash point 26” C.) or crude benzene were used with most success. To determine the most desirable proportions, a series of mixtures, containing from 50 to 90 per cent of the heavy constituent,were tested. It was found that a reduction of the volatile constituent below 30 per cent caused poor ignition, and that any great increase caused the trajectory to be poor, and produced a rolling type of flame which did not leave any unburned liquid a t the end of the stream. A mixture of specific gravity 1.02, containing 70 per cent water-gas tar and 30 per cent benzene heads, was first recommended. It gave an excellent trajectory, fierce flame, and good throw. Crude benzene was later substituted for the benzene heads, as being more readily available in the desired quantities Forty per cent crude benzene gives best results, but in hot weather i t can be reduced to 30 per cent. Approximately 30 per cent of this oil mixture is unburned a t the end of the trajectory, and in jet shooting as small a quantity of liquid as 0.5 gal. can be thrown the full distance of approximately 100 f t . Combinations of heavy and light liquids were used by the other warring nations, the actual liquids used being those most readily available. The British, French, and Italians used mixtures of heavy and light petroleum distillates with a specific gravity of about 0.86 a t 15” C. The Germans used various mixtures of heavy petroleum distillates or heavy wood-tar and coal-tar fractions with light petroleum distillates, coal-tar fractions or, sometimes, such liquids as methanol, acetone, and even ether. The specific gravity of the mixtures was usually about 0.96 at 15” C. The ignition of projected liquids was effected by us by means of a hydrogen pilot lamp a t the nozzle. Considerable experimentation with various other types of igniters was carried out, but the hydrogen pilot flame was considered best. It has the advantages, of course, of being nonluminous when the machine is not in action and giving positive ignition when needed.
Many methods of ignition were used by other nations. A cartridge of a slow burning, oxidizing agent-combustible mixture attached to the nozzle and ignited by an electric detonator or by friction was successfully used. In some cases incendiary hand grenades were thrown out to ignite the projected flammable liquid. When used in bombs and projectiles the flammable liquids may be absorbed in some such material as cotton or jute waste t o prevent too rapid volatilization and burning. Such an arrangement possesses the disadvantage that if the mass is scattered by an explosion the intensive incendiary action is lost, and if it is allowed to burn without scattering, the mass of absorbent material protects the target to a considerable extent. Liquids and mixtures of paraffin and light oils which are somewhat mushy have objectionable hydrostatic effects when used in drop bombs and projectiles. Besides the flammable liquids, various other organic materials, such as resins and pitches, have been used. Celluloid was used in several German incendiary devices and, mixed with resin, in a French bomb. SOLID OIL
The special incendiary material known as “solid oil” was developed as a result of an extended investigation of materials which could be used most effectively along with thermite in devices such as our 50-lb. drop bomb, which were designed t o set fire to heavy building constructions. It was early decided that such devices should contain some quick-reacting, great heat-producing material, such as thermite, and a greater amount of flammable material which, when ignited by the thermite reaction, would burn with a large hot flame for a considerable time, and actually render the target more readily flammable. Aside from these desirable properties, the material should present no great problems of manufacture, cost, transportation, or use. In early tests various oxidizing agent-combustible mixtures, pine pitches and rosins, heavy oils alone, and absorbent materials saturated with oils were tried, but all were found to possess undesirable properties. After comparative tests it was clearly seen, however, that the oils possessed the most desirable incendiary properties and that the only drawback to their use was their physical state. Experiments were accordingly started to determine the feasibility of solidifying satisfactory oil mixtures. It was well known, of course, that emulsions or gels could be prepared by the use of a number of colloidal substances. After considerable investigation a process was developed whereby we could prepare simply and cheaply a solidified oil mixture which has stood all the tests of permanence under conditions of transportation and use, and which has proved to be as near the ideal secondary incendiary material as could be desired. The mixture is run into the containers while still warm and fluid, and becomes solid on cooling. After the process had been in use for some time, Dr. H. G. Byers made a survey of the American, French, British, and German patents relative to solidifying fuel oils and, from the five hundred found, he selected forty-five as being most representative, and tested them in the laboratory. The products obtained were compared with the standard solid oil. He states that “none of the products were Found to compare very favorably with it. * * * Those that were found to approximate the standard oil now in use were much more complex and probably more expensive.” The flammable liquids used in the preparation of the material were selected after tests of over two hundred oils and mixtures had been made. A large number of highly flammable liquids burn a t a fairly low temperature, and such liquids will not effectively ignite the wood upon which they burn or render it highly flammable. Solidified alcohol is an example of such a material. Materials that vaporize very rapidly keep the wood cooled down below its ignition temperature. Furthermore, such materials burn so readily that they do not melt and spread so as to in-
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crease the area of attack. Solidified light oils and liquids with a low fire point are not satisfactory. On the other hand, solidified heavy oils and greases with a very high fire point are not satisfactory because they melt and burn too slowly, because the liquefied portion which runs away from the point of attack does not remain ignited, and because, in some cases, a residue which protects the wood is left upon burning. Our experiments showed that a solidified mixture containing a small percentage of a liquid having a relatively low fire point and a large percentage of a liquid having a moderately high fire point was most effective. Such a mixture burns readily, owing to the presence of the liquid of low fire point, and the burning of this liquid furnishes the heat necessary to melt the material and keep ignited the liquid of higher fire point which spreads over a large area, penetrates the wood, and actually renders it highly flammable. Certain readily available distillate fuel oils with a range of fire points from 170' to 225" C. were found to give most satislactory results. Distillation curves and fire-point determinations were of great value in the search for suitable liquids. The preparation of the solid oil on a large scale for filling the 50-lb. drop bombs presented no difficulties, and a plant for the work was put into operation a t Edgewood Arsenal. Besides its use in these large bombs, solid oil was also used or recommended for use in other devices such as Liven's drums, shell, grenades, certain other types of bombs, and in trench stoves. For this latter use a special stove was designed which permitted the oil to burn without smoke. Solidified kerosene was found to burn satisfactorily in these special burners. I n tests, 100 g. burned continuously with a luminous, nonsmoky flame for 6 hrs. In respect to heating power this material is greatly superior to the well-known solid alcohol.
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until homogeneous. The solution of phosphorus in carbon disulfide, prepared by introducing the phosphorus beneath the surface of the disulfide with as little exposure to air as possible, is added to the previously prepared oil mixture, and the container is closed and agitated to insure homogeneity. With proper precautions, the handling of the solution can be done without danger of premature ignition. The speed and spread of ignition are secured by the presence of the readily volatile constituents and the duration and intensity of the flame by the presence of the heavier combustibles. The mixture is not subject to detonation by shock and, having a low coefficient of expansion (0.0174 per O C. between -10" and 55') and a low vapor pressure (58 cm. at 50" C.), will not cause undue pressure in the containing device. It may be used alone or with an absorbent such as cotton waste in any sort of a device designed to carry liquid or semiliquid material. The %in. Liven's projectiles containing the mixture and cotton waste were quite effective in trials.
(Tobe concluded)
Assignment of Patents
On June 2, 1921, a decision was given by the Supreme Court of the State of New York in the case of the Air Reduction Company, Inc., against Warren R. Walker, a research chemist who refused to assign a patent to the company. The company is engaged in the manufacture and sale of oxygen, acetylene, calcium carbide, and oxyacetylene welding and cutting apparatus and in the development of processes and apparatus for the utilization of the elements of the atmosphere, and maintains a research laboratory for the study of the utilization of nitrogen, argon, neon, and other by-products of the manufacture of oxygen, under the direction of Floyd J. Metzger, chief chemist. SPONTANEOUSLY FLAMMABLE LIQUIDS The defendant was employed as a research chemist, and in March 1920 was engaged in an investigation on the commercial utiliFor the reason that it would require no ignition bevice and zation of neon under the direction of Metzger, devoting full thus could be advantageously used, a liquid was desired which time to this problem a t the sole expense of the company and fully understanding that the condition of his employment was would ignite spontaneously after a short exposure t o the atmos- the assignment to the company of all inventions made during phere, have an effective incendiary action, and be safe to handle his employment. In June 1920, an automobile indicator was and transport. Simple, spontaneously flammable liquids such devised which embodied a neon tube bent in the outline of a as zinc ethyl and carbon disulfide containing dissolved phos- hand and mounted in a casing with an induction coil, adapted for mounting on an automobile or other motor driven vehicle. phorus obviously could not satisfy the requirements, and con- This invention was patented by the company in the joint names siderable research was necessary before a satisfactory liquid was of Floyd J. Metzger and Warren R. Walker. As a result of further investigations, while still in the employ of the company, produced. I n the course of the research the possibilities of using such substances as phosphine, silicine, chromyl chloride, Walker materially improved the invention. Throughout the period of his employment the defendant never indicated an fuming nitric acid, permanganates, zinc ethyl, and phosphorus intention to claim any interest whatsoever in the invention, were fully investigated, and the substance found most suitable and, together with Metzger, executed the papers in connection with the filing of the application for the patent by the company. for the preparation of such liquids was phosphorus. A number of combinations of liquids were developed which When requested to execute an assignment of the application in order that the legal title might rest in the name of the company, gave satisfactory results as far as spontaneity of ignition was he refused to do so, although Metzger assigned his half of the concerned. But what was desired was a homogeneous liquid invention. The invention is of great value to the company, with the desired properties. Mixtures were made of various and the holding by the defendant of the legal title to a one-half oils with carbon disulfide and phosphorus containing these interest in the invention, the equitable title to which is in the plaintiff, might lead to the substantial damage of the company constituents in such proportions that the separation of no for which no adequate remedy a t law exists. In view of the solid or liquid layer resulted. The objection t o these mix- above findings of fact, the Court ruled that the plaintiff is the tures was that they lacked intensity of combustion, so the effect lawful owner of the entire right, title and interest in and to the of adding various nitrated organic compounds was tried. Of application for this patent in this and any foreign company, and that the defendant should assign it to the plaintiff and dethe nitro bodies, trinitrotoluene was found most satisfactory. liver to plaintiff all documents and models relating to the invenFinally, a mixture containing crude benzene, steam-distilled tion or any improvements made by him while in the employ of the plaintiff; that the defendant must give the plaintiff all fuel oil, gas-tar oil, carbon disulfide, phosphorus, and trinitrotoluene was developed which is satisfactory from the stand- information regarding patents on inventions made during his employment by the company; that the defendant is permapoints of simplicity of preparation, safety, and eff ective~ess. nently enjoined from making or selling any automobile indiBy varying the proportions of the constituents the ignition can cators embodying a tube containing neon as illustrated in be made to occur either almost instantly upon exposure or after above patent or improvements, from assigning to anyone except the plaintiff his rights in such patents, from filing any additional a considerable delay. application for patents on automobile indicators or any other In the preparation of the mixture the desired quantity of inventions made while in the employ of the plaintiff, and from trinitrotoluene is dissolved in thecorrespondingweight of benzene, attempting to interfere with the prosecution of the application the fuel oil and gas-tar oil are added, and the whole is stirred for the patent on this invention.
