Chapter I: Shrapnel Shells

In naval, coast defense and artillery operations, several types of explosive shells are used; the chief ones are: the armor-piercing shell, made to pierce armor-plate before exploding; shells exploded by means of a timing fuse; shells exploded by either a timing or percussion fuse; and shells exploded by percussion only. Each different shell has some definite function to fulfill, and is designed for that purpose. For field or artillery operations, the shrapnel and lyddite are the two principal types used. Of these, shrapnel is the most prominent, because of its destructive power and its interesting mechanical construction.

=Early Development of Shrapnel.=--The shrapnel shell was invented in 1784 by Lieut. Henry Shrapnel, and was adopted by the British Government in 1808. As is shown at _A_ in Fig. 2, the first shell was spherical in shape, and the powder or explosive charge was mixed with the bullets. Although this type of shell was an improvement over the grape and canister previously used, its action was not altogether satisfactory, as the shell, on bursting, projected the bullets in all directions and there was also a liability of premature explosion. In order to overcome the defects mentioned, Col. Boxer separated the bullets from the bursting charge by a sheet-iron diaphragm, as shown at _B_ in Fig. 2. This shell was called a diaphragm shell to differentiate it from the first shell of this type.

In the shell made by Col. Boxer, the lead bullets were hardened by the addition of antimony, and as the bursting charge was small, the shell was weakened by cutting four grooves extending from the fuse hole to the opposite side of the shell. Shells of spherical shape were first fired out of plain-bored guns, and upon the advent of the rifled gun it was necessary to add a circular base, which was made of wood and covered with sheet iron or steel to take the rifling grooves. The first shrapnel shells were made of cast iron, but a later development was to use steel and elongate the body, reducing it in diameter. The diameter of the bullets was also reduced so that a greater number could be contained in a slightly smaller space. The improved shrapnel was also capable of being more accurately directed.

=Shrapnel Shells of Present-day Design.=--Shrapnel shells, as used at the present time by the different governments, vary slightly in construction and general contour as well as in the constituents entering into their different members. As shown in Fig. 1, a completed shrapnel comprises a brass case carrying a detonating primer and the explosive charge for propelling the projectile out of the bore of the gun. The projectile itself comprises a forged shell that carries the lead bullets and bursting charge. Screwed into the front end is the combination timing and percussion fuse which can be set so as to explode the shell at any desired point, and from which the flame for exploding the bursting charge is conveyed through a powder timing train and a tube filled with powder pellets down through the diaphragm to the powder pocket.

Of these members of a shrapnel, the shell and timing fuse present the most interesting features from a mechanical standpoint. The shell used by most governments is made from a forging, machined to the desired dimensions in hand and semi-automatic turret lathes as well as in ordinary engine lathes. The fuse is an extremely accurate piece of mechanism, and is largely produced from screw machine parts, some of which, however, are forged previous to machining. The brass cartridge case--the next member of importance--is drawn from a brass blank by successive operations in drawing presses, and is indented and headed. Following this, several machining operations are performed on the head and primer pocket.

=Types of Shrapnel Shells.=--Shrapnel shells are made in two distinct types, one of which is known as the common shell, and the other as the high-explosive. The common shell is a base-charged shrapnel, fitted with a combination fuse, whereas the high-explosive shell is fitted with a combination fuse and, in addition, with a high-explosive head, the head also bursting and flying into atoms upon impact. The high-explosive shell is not ruptured upon the explosion of the bursting charge in the base, but the head is forced out and the bullets are shot out of the case with an increased velocity. In the meantime, the head continues in its flight and detonates on impact. This type of shell is not used as extensively as the common shrapnel, and, therefore, the common shrapnel shell alone will be taken up in the following.

=The Explosive Charge.=--Reference to Fig. 1 will show that as far as the construction of the shrapnel shell and case is concerned, there is very little difference in those employed by the various governments. Starting with the cases, it will be seen that these are almost identical, except for length and the arrangement of the head for carrying the detonating primer. There is a marked similarity in this respect between the Russian, the British, and the German, and between the American and the French. The form of the explosive charge held in the brass case differs in almost every instance, but without exception smokeless powder in some form or other is used. In the American shell, nitrocellulose powder composed of multi-perforated cylindrical grains each 0.35 inch long and 0.195 inch in diameter are used. In the Russian case, smokeless powder of crystalline structure is used. In the German, smokeless (nitrocellulose) powder in long sticks and arranged in bundles is held in the case. The French use stick smokeless powder ¹⁄₂ millimeter (0.0195 inch) thick by 12.69 millimeters (¹⁄₂ inch) wide. Two lengths or rows of this powder are arranged in the case. The British use a smokeless powder of crystalline structure somewhat similar to the Russian, but in some cases cordite has also been used, although of late this type of powder has not been quite as commonly employed.

The detonating agent or primer held in the head of the case varies in almost every type of shrapnel. Practically all primers are provided with “safety heads,” so that the shrapnel can be handled without danger of premature explosion. The object, of course, of the detonating agent or primer is to detonate or cause the sudden explosion of the explosive charge in the shell for propelling the shrapnel out of the field gun.

=The Shrapnel Shell.=--The shell itself, as previously mentioned, is made either from a forging or from bar stock. Forgings, however, are used to a greater extent than bar stock, because the forged shell is more homogeneous in its structure than the bar-stock shell, and piping--a serious objection in the bar-stock shell--is entirely eliminated. The shells used by the British, Russian, and German governments are made almost exclusively from forgings, whereas those used by the French and American governments are made both from forgings and bar stock. When the French shell is made from bar stock, an auxiliary base is screwed into it to eliminate any danger of piping. Near the base of all shells is a groove in which a bronze or copper band is hydraulically shrunk. This is afterward machined to the desired shape and takes the rifling grooves in the gun so as to rotate the shell when it is expelled. The body of the shell itself is slightly smaller than the bore in the gun, and the rifling band, which is larger and which is compressed into the rifling grooves, rotates the projectile, thus keeping it in a straight line laterally during flight. The bursting charge, which in practically all cases is common black powder, is carried in the base of the shell and is usually enclosed in a tin cup. Located above this is the diaphragm which is used for carrying the lead bullets out of the shell when the bursting charge explodes and distributes them in a fan shape. In most shells, upon exploding, the nose blows out, stripping the threads that hold the members together. It will, therefore, be seen that, in the explosion, the entire fuse, fuse base, tube, diaphragm and bullets are all ejected, the shell itself acting as a secondary cannon in the air.

The number of lead bullets carried in the 3-inch shrapnel shells ranges from 210 to 360. In all cases, the lead bullets are about ¹⁄₂ inch in diameter, weigh approximately 167 grains, and are kept from moving in the shell by resin or other smoke-producing matrix. The matrix put in with the lead bullets, in addition to keeping them from rattling, is also used as a “tracer.” It is of importance in firing shrapnel that the position of the explosion be plainly seen. With large shells this is not difficult, but with shrapnel for field guns at long range certain conditions of the atmosphere make it difficult to see when the shell actually bursts. Various mixtures are used to overcome this difficulty. In some cases, fine-grained black powder is compressed in with the bullets in order to give the desired effect. In the German shrapnel, a mixture of red amorphous phosphorus and fine-grained powder which produces a dense white cloud of smoke is used, and in the Russian, a mixture of magnesium antimony sulphide is used. The range of a 3-inch shrapnel shell is about 6500 yards, and the muzzle velocity of the quick-firing field gun ranges from 1700 on the American to 1930 feet per second on the Russian field gun. The duration of flight ranges from 21 to 25 seconds.

=Development of Timing and Percussion Fuses.=--The first fuses used in field ammunition were short iron or copper tubes filled with a slow-burning composition. These were screwed into a fuse hole provided in the shell, but there was no means for regulating the time of burning. Later--about the end of the seventeenth century--the fuse case was made of paper or wood so that by drilling a hole through into the composition the fuse could be made to burn for approximately the desired length of time before exploding the shell, or the fuse could be cut to the correct length to accomplish the same purpose.

For a considerable time all attempts to produce a percussion fuse were unsuccessful. Upon the discovery of fulminate of mercury in 1799, the chief requirement of a percussion fuse was obtained. About fifty years elapsed, however, before a satisfactory fuse was made. The first percussion fuse was known as the Pettman fuse, and comprised a roughened ball covered with detonating composition that was released upon the discharge of the gun. When the shell hit the desired object, the ball struck against the inner walls of the fuse, exploded the composition and powder charge, thus bursting the shell. There are at the present time three principal types of fuses in use: First, those depending on gas pressure in the gun setting the pellet of the fuse free--this is a base fuse; second, those relying on the shock of discharge or the rotation of the shell to set the pellet free--used in nose and base fuses; third, those depending on impact.

In shrapnel shells advantage is taken of two types of fuses, one of which is the combination timing and percussion fuse used on common shrapnel, and the other the combination timing and percussion fuse of the high-explosive type used on high-explosive shrapnel. These types of fuses are again sub-divided, but only in the manner of construction. The most common fuse is that known as the combination timing and percussion fuse of the double-banked type. This is used in practically all shrapnel fuses except the French. The advantage of the double ring of composition shown at _A_ and _B_ in Fig. 3 is to give a greater length of composition and more accurate burning. Triple-banked and quadruple-banked fuses on the same principle have been designed, but at the present time have not been introduced.

=Operation of Combination Timing and Percussion Fuses.=--The manner in which the combination timing and percussion fuse is regulated to discharge the bursting charge in the shrapnel shell is interesting and involves extremely difficult mathematical calculations. Before going into the method of setting the fuse, it would probably be advisable to describe briefly just how the fuse operates. As an example of the double-banked fuse, Fig. 3 shows that adopted by the United States government. The following description applies to this type of fuse.

Assume, first, that the timing ring is set at zero. The propelling force given to the shrapnel shell in leaving the bore of the gun is such as to sever the wire _C_ from plunger _G_. Plunger _G_ carries a concussion primer which is discharged by hitting firing pin _D_. The flame passes out through vent _E_, igniting the powder pellet _F_ and the upper end of train _A_, and then through the vent _H_. From here, the flame is transmitted to the lower timing ring _B_ through vent _I_ and the magazine _J_, and from there through the tube to the bursting charge in the base of the shrapnel shell.

Assume any other setting, say 12 seconds. The vent _H_ is now changed in position with respect to vent _F_ leading to the upper timing train, and the vent _I_ leading to the powder magazine _J_ is also changed. The flame, therefore, now passes through vent _E_ and burns along the upper time train _A_ in a counterclockwise direction until the vent _H_ is reached. It then passes down to the beginning of the lower timing train and burns back in a clockwise direction to the position of vent _I_, from which it is transmitted by the pellet of compressed powder in this vent to the powder magazine _J_. It should be understood that the annular grooves in the lower face of each timing train do not form complete circles, a solid portion being left between the grooves in the ends of each. This solid portion is used to obtain a setting at which the fuse cannot be exploded and is known as the “safety point.” As shown in Fig. 6, it is marked _S_ on the adjustable timing ring.

The timing fuse shown in Fig. 3 is of the combination timing and percussion type, and if the wire _C_ fails to release percussion plunger _G_, the shell is exploded by means of a percussion fuse which comes into use when the shell strikes. The percussive mechanism consists of a primer _K_ held in an inverted position in the center of the fuse body by a cup located beneath the percussive primer. Percussion plunger _L_ works in a recess in the base of the fuse body and is kept at the bottom of the recess away from contact with the primer by a light spring in plunger _M_. The firing pin _N_ is mounted on a fulcrumed pin, and is normally kept in the vertical position by means of two side spring plungers. When the shell strikes, the impact causes the plunger to snap up against the primer after compressing the spring in pin _M_. This causes the firing of the primer _K_ and the explosive charge passes out through a hole in the percussion plunger chamber, not shown, to the magazine _J_ and from there down to the powder in the base of the shell

=Russian Fuse.=--The Russian fuse shown in Fig. 4 differs only in a few minor details from the American fuse, the chief difference being in the arrangement of the percussive mechanisms. The percussive plunger for the timing arrangement is kept up from the firing pin by means of a spring bushing _E_ surrounding the body of the plunger. This bushing is expanded by the plunger which is forced through it due to the force of the shrapnel in leaving the bore of the gun. The spring _B_ in the head of the fuse assists the plunger in expanding bushing _E_ and in dropping down onto the firing pin _C_. The flame from the exploded primer then travels down to the powder in the shell in practically the same way that it does in the American fuse, except that the magazine chamber is located at _D_ and explodes through the impact fuse chamber. The percussive arrangement for setting the shell off by impact is slightly different from that in the American fuse, in that the primer and firing pin are held apart by means of springs, the inertia of which is overcome when the shell strikes an object.

=French Fuse.=--With the exception of a few minor details, the timing fuses used in American, Russian, British, German, Japanese, etc., shrapnel shells are the same. The French timing fuse, however, as shown by the diagram Fig. 5, operates on an entirely different principle. In this fuse, the firing for the timing train is contained in a sealed tube of pure tin and is wound spirally around the head of the fuse. Inside of the head is the ignition arrangement. To set the timing part of this fuse, it is placed in a fuse-setting machine attached to the field gun and, by forcing down a handle on this device, a piercing point is thrust through the outer cap of the fuse, penetrating to the interior space of the head as shown at _A_. Upon the discharge of the shell from the gun, the gas pressure forces firing pin _B_ back, hitting the percussive primer _C_. This causes a flame which passes out through the opening previously punched at _A_ and ignites the “rope” powder fuse which is wound around the head of the fuse body. This type of fuse is also provided with a fuse which sets off the shell by impact should the timing fuse fail to work. The head of the fuse is covered with a cap with holes for the piercing point, and the whole cap can be shifted around for a short distance and set by the corrector scale marked on the body, as shown in Fig. 1. A projection on the cap engages a recess in the fuse-setting machine and provides for this movement.

=Firing of Shrapnel.=--The accuracy with which a shrapnel can be exploded in the air at any desired point is remarkable, considering the number of variable quantities that enter into the construction of the timing fuse and powder train, etc. The calculations necessary for finding the correct setting on the timing ring involve, however, the use of higher mathematics and are consequently not within the scope of this treatise.

In Fig. 6, the timing ring used on the American fuse is shown. Here it will be seen that the ring is provided with twenty-one graduations corresponding to twenty-one seconds in the duration of flight of the projectile. It will also be noticed that the spacing of the graduations differs. The reason for this is found in the relation of the vents, the positions of the lower timing train, the trajectory of the flying missile, and the decrease of velocity.

Diagram Fig. 7 shows in an interesting manner just how a shrapnel is fired. The range is approximately obtained by panoramic sights or other means, and a test shell fired, the point of explosion noted, and the necessary corrections made. A table which has been worked out for different distances is then used. In Fig. 7 the diagram shown pertains to the American quick-firing field gun having a muzzle velocity of 1700 feet per second and the American shrapnel of 3-inch size. It will be noted that at 2000 yards the terminal velocity of the shrapnel is 1038 feet per second and the time of flight for the projectile 4.75 seconds. In other words, the timing train to explode the shrapnel at this point would be set at _A_ in Fig. 6. The range of a 3-inch American shrapnel is 6500 yards and at this point the terminal velocity is approximately 724 feet per second, the time of flight 21.92 seconds. The shrapnel, when exploded, shoots out the bullets at an increased velocity or from 250 to 300 feet per second, covering an area of about 250 by 30 yards, half the bullets falling on the first 50 yards of the beaten zone.

In manufacturing shrapnel shells, a test shell is taken from every 120 shells, which is actually fired out of a quick-firing gun into a bank of sand. If the contour of the shell in the neighborhood of the powder pocket is expanded during this test, the shell is discarded because of the liability of tearing out the rifling grooves in the gun

=Propellants and Explosives used in Shrapnel and High-explosive Shells.=--As has been previously explained, a shrapnel shell contains three principal parts, _viz._, the projectile that carries the destructive charge of lead bullets, the fuse that carries a detonating arrangement for exploding the charge in the base of the projectile, and the cartridge case that carries the powder charge used in propelling the projectile out of the bore of the gun. A high-explosive shell also comprises three principal parts, but the projectile, instead of carrying a charge of bullets and black powder, is filled with a high-explosive material, which, when detonated, bursts the body of the projectile into small pieces that are thrown off with great velocity and destructive effect. Shrapnel is used against troops in the open field, whereas high-explosive shells, which may be either of the ordinary or of the armor-piercing type, are used against fortifications, etc

=Classification of Explosives.=--The explosives used in shrapnel and high-explosive shells may be divided into three general classes: 1. Progressive or propelling explosives--known as “low” explosives. 2. Detonating or disruptive explosives--known as “high” explosives. 3. Detonators--known as “fulminates.” The first of these includes black gun powder, smokeless powder, and black blasting powder. The second, dynamite, nitroglycerine, gun cotton, etc. The third includes chiefly fulminates and chlorates. In all classes of explosives, the effect of the explosion is dependent upon the quantity of gas and the heat developed per unit of weight and volume of the explosive, the rapidity of the reaction, and the character of the confinement, if any, of the explosive charge.

_Low Explosives._--For certain explosives, such as smokeless powder, the explosive action does not differ in principle from the burning of a piece of wood or other combustible material. The combustion is very rapid, but is a surface action, progressing from layer to layer until the entire grain is consumed. Such materials are known as “low” explosives, although the power developed through the combustion of a unit weight may be very great. The progressive emission of gas from a low explosive, such as burning gun powder, produces a pushing effect upon a projectile without unduly straining the gun, whereas the sudden conversion of an equal weight of a high explosive, such as nitroglycerine, into gas, would develop such high pressures as to rupture the gun.

_High Explosives._--In high explosives, such as nitroglycerine, gun cotton, picric acid, etc., the progress of the explosive reaction is not by burning from layer to layer, but, instead, consists of an initial breaking up of the molecules, giving rise to an explosive wave, which is transmitted with great velocity in all directions throughout the mass, and causes it to be converted almost instantly into a gas. The velocity of this explosive wave has been determined, for some materials, to be more than 20,000 feet, or approximately four miles, per second.

_Detonators or Fulminates._--The action of fulminates is much more powerful than either the low or high explosives described. They can be readily detonated by slight shock or by the application of heat, and are used in primers, for setting off the propelling charge in a cartridge case, and in fuses, either of the plain percussion or of the combination time and percussion types. The most common fulminate is made by dissolving mercury in strong nitric acid and then pouring the solution into alcohol. After an apparently violent reaction, a mass of fine, gray crystals of fulminate of mercury is produced. The crystalline powder thus produced is washed with water to free it from acid and is then mixed with glass ground to a fine powder. Because of its extreme sensitiveness to heat produced by the slightest friction, it is usually kept soaked in water or alcohol until needed

=Manufacture of Black Powder.=--Black powder, because of its “pushing” effect when exploded, is used extensively as a base charge for shrapnel shells in expelling the bullets from the projectile. It comprises three principal elements in about the following proportions: 75 parts of saltpeter, 15 parts of charcoal, and 10 parts of sulphur. These ingredients must be absolutely free from impurities and, in manufacturing, great care is taken in refining the saltpeter and sulphur, and in burning the charcoal, to prevent the introduction of any foreign substances. After purification, the ingredients are carefully weighed in the proper proportions and mixed for about 5 minutes in a revolving drum provided with mixing arms. The mixed charge is now ground for several hours, the charge being moistened occasionally with distilled water, the resulting mixture being what is called a “milk cake.” It is then reduced to fine meal in a machine having Tobin bronze or gun-metal rollers, after which it is compressed under hydraulic pressure.

The next operation comprises the granulating of the powder, which is done in a strong Tobin bronze or gun-metal framework carrying two pairs of toothed and two pairs of plain Tobin bronze or gun-metal rollers. The “cake” is cut into pieces by these rollers and falls on screens which sift it into grains of the required size. The grains are then separated from the dust in a revolving screen, and the high polish or glaze is produced by putting the powder into drums or glazing barrels, which revolve constantly for several hours. Graphite is generally used to provide the glazing effect. The powder is now dried in a stove heated by steam pipes, and is spread upon canvas trays placed on shelves

=Manufacture of Smokeless Powder.=--Smokeless powder, which is used in various forms in cartridge cases, was discovered in 1846 by a German chemist Schoenbein. The chief ingredient of smokeless powder is cotton. The portion of cotton used is generally the short fiber. The first attempts to produce gun cotton were unsatisfactory, and several very serious explosions occurred. Many of the difficulties in its manufacture were overcome by an Austrian, von Lenk. Still further progress was made by a Swedish engineer, Alfred Nobel, and the improved explosive was patented in 1888 under the name of “ballistite.” One of the principal smokeless powders is known as “cordite”, this name being derived from the cord-like form it assumes in manufacture. The first compositions of cordite were: 58 per cent of nitroglycerine; 37 per cent of gun cotton; and 5 per cent of mineral jelly. This composition, after considerable use, was found to have a slight deteriorating effect on the bore of the gun, and after ten years’ use was modified to the following proportions: 30 per cent of nitroglycerine; 65 per cent of gun cotton; and 5 per cent of mineral jelly.

The brand of smokeless powder used most extensively as a propelling charge in shrapnel or high-explosive shells is known as nitrocellulose, and, as is common with cordite, the base of this is cotton, as previously explained. It is manufactured as follows: After bleaching and purifying, the cotton is run through a picker which opens up the fibers and breaks up any lumps. It is then thoroughly dried and is ready for nitration. The most generally used method of nitration is to put the cotton into a large vessel filled with a mixture of nitric and sulphuric acids. The sulphuric acid absorbs the water developed in the process of nitration, which would otherwise too greatly dilute the nitric acid. After a few minutes’ immersion, the pot is rapidly rotated by power, and the acid permitted to escape. Following this, the nitrated cotton is washed for a short time and then removed from the nitrator or pot and repeatedly washed or boiled to remove all traces of free acid. As the keeping qualities of the nitrated cotton are dependent upon the thoroughness with which it is purified, the specifications for powder for the United States army and navy require that the nitrocellulose shall be given at least five boilings at this stage of the manufacture, with a change of water after each boiling, the total time of boiling being forty hours. Following this preliminary purification, the nitrocellulose is cut up into shorter lengths, by being rapidly run between cylinders carrying revolving knives. This operation--known as “pulping”--is necessary because of the difficulty experienced in removing the free acid, unless the fibers are cut up into short lengths.

After pulping, the nitrocellulose is given six more boilings, with a change of water after each, followed by ten cold water washings. The material is now known as gun cotton or pyrocellulose. Previous to adding the solvent, this must be free from water. This is generally accomplished in a circular wringer, and in addition by compressing the pyrocellulose into solid blocks. Alcohol is forced through the compressed mass. Ether is then added to the pyrocellulose already impregnated with alcohol, the relative proportions being two parts, by volume, of ether to one part of alcohol. After the ether has been thoroughly incorporated in a kneading machine, the material is placed in a hydraulic press and formed into cylindrical blocks about 10 inches in diameter and 15 inches long. It is then transferred to a finishing press where it is again forced through dies and comes out in the form of long strips or rods, which are cut into pieces of the length and widths required. It is in this finishing process that the various governments differ in their methods of manufacture. The United States Government uses a short perforated circular block, whereas the French use flat sticks about 0.0195 inch thick by ¹⁄₂ inch wide. Two lengths or rows of these sticks are arranged in the cartridge case. The cut up pieces are subjected to a drying process which removes nearly all the solvent and leaves the material in a suitable condition for use. The drying process is a lengthy one, amounting to as much as four or five months for powder in large pieces. Upon completion, the powder is blended and packed in airtight boxes

=Manufacture of High Explosives.=--The explosive charges used in high-explosive shells are known by various trade names, such as: emmensite, lyddite, melinite, maximite, nitrobenzole, nitronaphthalene, shimose, trinitrotoluol, turpenite, etc. The base of such explosives as emmensite, maximite, lyddite, melinite, and shimose, is picric acid, which is secured from coal tar, subjected to fractional distillation. The liquid which comes off when this is raised to a temperature of 150 degrees C. is called “light” oil, and when these light oils have been again distilled, the next fraction or “middle” oil yields phenol or carbolic acid. This substance when nitrated gives off picric acid. Experiments with lyddite shells showed their behavior to be very erratic, some exploding with great effect, while others gave disappointing results. This was due to the fact that picric acid requires a powerful detonator to obtain the highest explosive effect. The use of such a detonator, however, is dangerous, and extensive experiments have brought forth a new high explosive known as trinitrotoluol--generally termed T.N.T. Although the explosive force of trinitrotoluol is slightly less than that of picric acid, the pressure of the latter being 135,820 pounds per square inch as against 119,000 pounds for trinitrotoluol, its advantages more than compensate for the difference.

Trinitrotoluol is obtained by the nitration of toluene, contained in the crude benzol distilled from coal tar and washed out from coal gas. The crude benzol contains roughly:

Per cent
Benzine 50
Toluene 36
Xylene 11
Other substances 3

Toluene to be used for the manufacture of trinitrotoluol should be a clear water-like liquid, free from suspended solid matter, and having a specific gravity of not less than 0.868, nor more than 0.870, at 15.5 degrees C. Trinitrotoluol when pure has no odor and is a yellowish crystalline powder which darkens slightly with age. It cannot be exploded by flame or strong percussion, and a rifle bullet may be fired through it without any effect. When heated to 180 degrees C., it ignites and burns with a heavy black smoke; but when detonated by a fulminate of mercury detonator, it explodes with great violence, giving off a black smoke. Shells containing this explosive, first used on the western battle front, were given such names as “coal boxes,” “Jack Johnsons,” “Black Marias,” etc., by the allies.

The Russians and Austrians use a high explosive known as ammonal in which 12 to 15 per cent of trinitrotoluol is mixed with an oxidizing compound, ammonium nitrate, a small amount of aluminum powder, and a trace of charcoal. This high explosive gives somewhat better results than plain trinitrotoluol, but has the one disadvantage of easily collecting moisture, and consequently must be made up in airtight cartridges. The British are now using an improved compound of this character, which is so prepared that trouble is not experienced with the collection of moisture.