in the fixed socket, and formed internally to take the shoulders of the shell, the fuze projecting downwards through a hole in the bottom of the holder. Fixed about the middle of this movable socket is a gear-wheel, and internally, in its bottom, is a small mortise into which a tenon on the fuze engages so that the fuze and shell always occupy a fixed position in the holder. The shell is inserted nose downwards in the holder, secured by the mortise and tenon, and the holder is then, by means of suitable gear in the box operating the gear-wheel, screwed down into the fixed socket, carrying with it the shell and fuze, until the appropriate point in the worm scale of the fuze comes opposite a punching tool in the fixed socket, at which point the tool, operated by an external hand lever, punches the cover, lead tube and body as before described. The amount of screwing-in is determined by the number of turns (or fractions of a turn) of the holder gear-wheel, and the internal gear of the box which actuates this gear-wheel is so controlled by a handle on the top of the box that the position of the handle relatively to a dial1 on the box exactly represents the position of the fuze scale relatively to the punching tool in the fixed socket. (In practice the handle is set and the holder socket screwed in first, the shell inserted and keyed next, and the actual punching comes last.)

The French service débouchoir is made with two sets of elements side by side having a common dial, corrector scale and setting handle, but separate punching handles. This enables two fuzed shells to be set simultaneously for the same time of burning or successively for different times as desired.

AUTHORITIES.-No recent book descriptive of fuzes has been published, in the ordinary sense of the word. Information during the war period was circulated only amongst those professionally concerned. The information given above has been collected from various papers and memoranda of this kind, and chiefly from those supplied by the authorities of Woolwich Arsenal, to whom, and to Lt.-Col. G. O. Boase in particular, thanks are due. (C. F. A.)

MACHINE GUN, RIFLE AND PISTOL Since 1910 rapid strides have been made in the improvement of old and development of new designs of ammunition for machine guns, rifles and pistols, principally due to the World War. The manufacture of small arms ammunition, used by the various nations, may be briefly described by outlining the operations necessary to produce a standard cartridge of any one country. In general, these operations would apply to the manufacture of any cartridge, although slight departures therefrom would be necessary where the designs vary. The metallic components of a cartridge are the case, primer (without chemical composition) and bullet.

The Cartridge Case is made of cartridge brass which, as produced commercially, contains about 67% copper and 33% zinc. The brass is furnished in strips, coiled in convenient lengths, which are passed through automatic machines to produce metallic cups, from which the finished cases are evolved by a series of processes generally similar to those described for heavy gun cartridge cases.

The Primer, inserted in the head of the cartridge case, consists of a cap made of primer brass into which is inserted a percussion compo sition usually weighing from 25 to 40 grain, according to the character of the composition. After the assembly of the components, the primer is subjected to a drying operation for a short time to

The zero of this dial is itself adjustable relatively to a fixed fuzecorrector scale. For the theory of the corrector see 2.692, par. 29 and footnote.

|

insure that no moisture remains in the chemical mixture. After inspection it is inserted into the primer pocket and a drop of shellac placed in the joint between the primer and the cartridge case to provide water-proofing.

The Bullet (unless it be of special type such as armour-piercing) consists of a jacket surrounding a core. This jacket is made from cupro-nickel which, as furnished commercially, contains from 80% to 85% copper and from 15% to 20% nickel. The cupro-nickel is furnished in coiled strips from which by automatic machines cups are produced. These cups are subjected to a series of drawing operations after which the nose and profile of the bullet are formed by swedging processes. The core, of lead hardened with antimony or tin, may or may not be inserted before the bullet jacket is swedged to form. Finally, the composite bullet is resized and prepared for union with the cartridge case.

In assembling the complete round the primed cartridge cases are shellacked in the mouth for water-proofing, and are loaded by automatic machines with a propellant powder charge weighing from 40 to 50 grains. The bullets are then inserted into the mouths of the cartridge cases and secured by crimping the top edges of the cases into the cannelures provided (or otherwise, according to the design of the cartridge in question). Small arms ammunition of the various countries is designed and loaded to give muzzle velocities varying from 2,200 to 2,800 ft. per second, with maximum pressures never exceeding 60,000 lb. (27 tons) per sq. inch. Cartridge clips for quick loading are used in some form with practically all magazine rifles. The number of cartridges in a clip is usually five, placed one above the other. These clips are usually made with a body of rust-proofed steel or brass containing a flat brass spring.

The loaded ammunition, after being weighed, inspected and clipped, is classified and packed according to its future use. In the United States, ammunition passed as suitable for both rifles and ground machine guns is packed for issue in bandoleers made of olivedrab cloth, which generally contain six boxes each holding two clips. In most armies such individual packets of ammunition are put up in larger, metal-lined boxes, the number of rounds packed in a box and therefore its weight varying in different countries according to the preferences of the military authorities in each.

Packing-boxes are provided with watertight metal liners. In the United States the packing-box when loaded with ammunition weighs approximately 110 lb.; in Great Britain (mark VII. ammunition), 75 to 80 lb.

Ammunition for Machine Guns may be divided into two general classes: first, that for use in machine guns on the ground; and second, that for use in aircraft machine guns. The extensive use of ammunition for machine guns in the World War involved no new processes of manufacture in order to adapt it to the particular weapons. It did, however, require a more rigid inspection system in order to insure that the ammunition produced was of a quality suitable to stand the wear and tear of machine-gun action.

Ammunition for ground machine guns is generally the same as the standard type used in the shoulder rifle, but more rigidly inspected and tested. Several of the belligerents in the World War developed special types of cartridges having heavier bullets than their standard types for use in machine-gun barrage fire.

A number of special types of machine-gun ammunition have been developed for use by aircraft, all of which have the same overall length as the service ammunition and may be briefly described as follows:

The tracer cartridge, as the name implies, is loaded with a tracer bullet for use with machine guns where, as in aircraft work, it is essential to make the trajectory visible. The bullet differs materially from that of the service cartridge, in that the lead core of the latter is replaced by a conical lead slug in the nose of the tracer bullet jacket, in the rear of which there is inserted a gilding-metal capsule which contains the tracer composition. The ingredients used in the composition are dependent upon the type of trace desired. The red tracer involves the use of strontium salts with the necessary oxidizing agents, while the so-called white tracer gives off a greenish-white flame and involves the use of the barium salts with oxidizing agents, The tracer composition is compressed into the capsule at a pressure to withstand that produced by the exploding cartridge and the length of trace can be regulated by the adjustment of the pressure or amount of oxidizing agents used in the chemical mixture. The composition is ignited by the propellant powder flash and burns with a bright light during a minimum of 500 yd. of flight. Tracer cartridges are generally loaded so as to give the same ballistics as the service ammunition at 500 yards. As these cartridges are placed in machine-gun belts, interspersed with service, incendiary and other types of special aircraft ammunition, a distinctive marking is provided so that inspection may be made of each ammunition belt before the aviator goes into the air. and dirigibles

Owing to the extensive

observation balloons a

in the war, the demand was created for an incendiary bullet which

would ignite gases or other materials with which it might come in contact. Omitting technical detail, this form of bullet is organized to contain a charge of yellow phosphorus coated with copper phosphide or aluminium dust in the head. The base is sealed, but a small hole is punched in the side of the bullet and closed with an easily fusible alloy containing a high percentage of bismuth. The heat generated by the passage of the bullet through the barrel of the gun causes this alloy to melt, at the same time causing the yellow phos phorus to become molten. Upon exit from the barrel, the centrifugal force produced by the spinning of the bullet throws the molten phosphorus through the side hole and upon contact with the air the phosphorus burns leaving a trail of smoke and fire streaming from the bullet. Incendiary bullets burn over a range of approximately 300 yd. and are so loaded as to shoot similarly to service ammunition at that range. Incendiary cartridges are distinguished from other types of ammunition by special markings.

Combinations of the various types of bullets described above have been tried out experimentally with different degrees of success. The inspection of all of these types is very rigid, as all ammunition for aircraft use must be specially selected, in particular because hangfires may be dangerous in aircraft machine guns synchronized with the propeller.

Many types of armour-piercing bullets were used during the World War in order to attack the light armour-plate of aeroplanes, tanks, etc. This class of bullet, with its steel core, required considerable experimental work and may still be considered as in the development stage. It consists principally of a cupro-nickel jacket, inside which is a hardened steel core incased in a lead envelope. The action may be briefly described as follows:—

Upon striking the armour-plate, the jacket splits and a portion of the lead in the nose of the bullet is trapped between the hardened point of the steel core and the surface of the hardened armour-plate. This soft mass of lead produces a protective coating for the nose of the steel core and thus aids penetration. The bullet is loaded into the same case as the service ammunition and is distinguished by special markings. A larger calibre of armour-piercing ammunition was developed by the Germans for the 13-mm. anti-tank rifle (see RIFLES). The bullet was of the armour-piercing type and weighed approximately 800 grains, while the cartridge case was of the semirimless type with a propellant charge of about 200 grains. This cartridge developed a muzzle velocity of about 2,450 f.s. and was very effective against tank armour. Further developments along this line may be expected in the future.

Ammunition for Rifles.-Each country has its standard rifle cartridge which is of the same shape and size and is manufactured in the same manner as the machine-gun ammunition above described. Some of these cartridges are of the rimmed while others are of the rimless type. The standard calibres vary from .25 in. to 32 inch. Various other types have been developed for guard, test, and training purposes, such as the blank, dummy, guard, high-pressure, and gallery-practice cartridges.

Ammunition for Pistols.-The ammunition used in various countries in automatic pistols is very similar, and a description of the manufacture of the United States type may be considered to be representative of all others. This cartridge consists of a drawn brass case with a primer inserted in its head. The bullets, as a rule, have jackets made from drawn gilding metal or some other suitable material. The manufacture of the cartridge case and bullet-jacket follows, in general, the process outlined for the manufacture of the rifle-cartridge components except that the number of operations is considerably reduced. The bullet is 45 calibre, weighs 230 grains and has its jacket tinned and filled with a core of lead hardened with about 2% of antimony. The cartridge cases are all of the rimless type and have a small cannelure located on the cartridge case in such a position as to prevent a bullet from being pushed back into it. All pistol ammunition is loaded to give low velocities as compared with rifle ammunition. Calibre 45 cartridge, used by the United States, has a muzzle velocity of 800 f.s. and develops a maximum pressure of 16,000 lb. per sq. inch. In addition to the pistol cartridges of the service type, there are blank and high-pressure cartridges for instructional and testing purposes. The ammunition made for automatic pistols of smaller calibre, used by travellers, police and others, is in principle similar to that of the heavier 45 pistol. (W. L. C.)

AMUNDSEN, ROALD (1872- ), Norwegian polar explorer, was born at Borge, Smaalenene, Norway, July 16 1872, the son of a shipowner. He was educated at Christiania and afterwards

REGIONS). In June 1918 Amundsen left Norway in the " Maud " with the intention of drifting across the Arctic ocean, but at the end of 1919 was forced to abandon the attempt (see ARCTIC REGIONS). Capt. Amundsen has published The North-West Passage (1907), and The South Pole (1912), and has received many honours from learned societies.

ANAESTHETICS (see 1.907). In connexion with the progress made in 1910-20, it is somewhat remarkable that the agents for producing general surgical anaesthesia which were the first to be introduced, that is, nitrous oxide gas, ether and chloroform, not only remained in general use, but actually provided in greater part for the requirements of modern surgery. "Regional" anaesthesia, or analgesia as some prefer to call it, had, however, in part supplanted "general" anaesthesia. It consists in abolishing sensation in a restricted part of the body without affecting consciousness; it is effected by "blocking" the conduction of sensation through the nerves supplying the area concerned by applying to them a solution of a drug similar in constitution to cocaine, or by injecting this solution into the lower part of the spinal canal and so blocking the sensory fibres in the nerve roots and in the spinal cord itself. Regional anaesthesia has, however, as yet only a limited application, for although adopted as a convenient routine measure in some classes of cases and types of patients, yet it has been found by experience to have certain limitations, and in the case of spinal anaesthesia certain dangers. Many persons, moreover, prefer the blissful ignorance of a general anaesthesia to full consciousness, and passive submission to a trying ordeal, even when they are deprived of sensation and when the sight of the operation is hidden from them.

General anaesthesia produced by the inhalation of a gas or vapour remains the routine procedure. The use of non-volatile drugs, such as morphia or hedonal, introduced by the mouth or by subcutaneous or intravenous injection, is not readily subject to control; once introduced these substances remain in the body until slowly excreted by the kidneys; the dose can be increased but it cannot be decreased, and herein lies a danger. Inhalation anaesthesia on the other hand is susceptible of the most delicate adjustment to requirements. The pulmonary route is adapted anatomically to meet the vital requirements of the absorption and excretion of the blood gases, oxygen and carbon dioxide, and is hence perfectly adapted for the passage to and from the blood of other gases and vapours. The amount of a vapour absorbed by the blood and the rapidity of its absorption are both proportional to its concentration in the atmosphere inhaled into the lungs so that the task of the anaesthetist is mainly one of adjusting the strength of the vapour according to the result which is desired. So also the amount which has been introduced into the blood can be rapidly reduced; it is partially exhaled on diminishing the strength of the vapour presented to the blood, and it becomes totally exhaled on withdrawing the vapour entirely from the inhaled atmosphere. This facility of the adjustment of anaesthesia is not shared by any other method, and it appears likely to sustain inhalation anaesthesia in its present predominant position for some time to come.

1 In the case of chloroform there is a deviation from the laws of the solution of vapours, but this is negligible at the low concentrations employed for anaesthetic purposes.

Nitrous Oxide. One of the surgical lessons of the World War was that persons suffering from severe shock and loss of blood from wounds did not progress favourably following operation under chloroform or ether, but that the prospects of recovery were distinctly improved when performed under the continuous inhalation of nitrous oxide gas. The reasons for this cannot be stated precisely, but it may be said in general terms that nitrous oxide is less depressing, and further that owing to its exceedingly rapid excretion, consciousness and normal bodily conditions are quickly restored after completion of the operation.

46

Nitrous oxide, or laughing gas" as it was formerly termed, is familiar as an agent for producing brief periods of narcosis, as for the extraction of teeth. When administered thus in a pure state it excludes the admission of air to the lungs, and if continued would cause complete asphyxia; the problem of continuous administration is therefore the admission of sufficient oxygen to the lungs to satisfy the needs of the body. Air contains about one-fifth of its volume of oxygen, but if nitrous oxide were diluted to this extent its partial pressure would be reduced to about 80%, which is too weak for the convenient production of its full anaesthetic effect, at least in the early stages of its administration. It is possible, however, to reduce the amount of oxygen inhaled below the normal quantity without reducing the oxygen in the blood to the same degree; this is due to the fact that the absorption of oxygen by the blood is a process of loose chemical combination with the haemoglobin, which is not governed by the laws of the simple solution of gases. Oxygen may in fact be reduced to a proportion of one-tenth of an atmosphere without causing discomfort to the patient or even under ordinary circumstances causing the discolouration of the face known as cyanosis. It may even be reduced lower than one-tenth and yet be capable of sustaining life. The continuous administration of nitrous oxide mixed with oxygen is thus made possible by the provision of a sufficiently delicate mechanism to regulate and indicate the relative proportions of the gases. One form of indicator which has been generally adopted consists of pressure dials connected with the supply tubes from the cylinders of compressed gases; these register the pressures at which the gases are supplied, and the proportions are in the same relation as the pressure of flow. Another form of indicator is that known as a sight-feed," in which the gases bubble through a glass vessel containing water, the flow being regulated so that one bubble of oxygen passes for a given number of nitrous oxide bubbles according to desire.

The continuous administration of nitrous oxide and oxygen is not, however, a method which is adapted for all classes of cases; the relaxation of the body muscles is not sufficient for the convenient performance of certain operations; the narcosis is not always sufficiently deep, and it may have to be supplemented by an admixture of ether vapour; nor is it a method absolutely free from danger. Its advantages in the cases of profound shock referred to appear to be undoubted, but how far it can be adapted for general purposes is as yet undecided.

son, or to

"from

the

Ether. The use of ether as an anaesthetic has received considerable stimulus from the introduction of the " open method of administration. In order to induce anaesthesia in a muscular perget him under" in ordinary phraseology, a strong vapour may be required, as strong as 25% to 30% in some cases, and it was formerly supposed to be impossible to attain sufficient concentration from ether sprinkled on a piece of fabric stretched on a frame or "mask." In order to attain this end a "close" method has been in general use, in which the patient breathes to and from a rubber bag over a surface of ether. In this way the vapour becomes concentrated in the bag, but at the expense of the oxygen of the contained air, which becomes rapidly used up, so that the inhaler must be removed periodically to allow of an inspiration of pure air in order to obviate total asphyxia. This method is effective, but far from ideal; the patient is generally more or less "blue partial asphyxia throughout the administration, there is a profuse secretion of slimy mucus which must be continually wiped away, the respirations are greatly exaggerated from "re-breathing carbon dioxide which accumulates in the bag, and they are often at the same time partially obstructed from the pressure of the closely fitting face-piece. The after-effects are generally unpleasant and not infrequently distressing. In the "open ether method the breathing is noiseless, effortless, and only slightly exaggerated, so that delicate abdominal operations can be performed with comfort. The flow of saliva is considerably less than in the closed method (probably from the absence of asphyxia) and this can be entirely abolished by the subcutaneous injection of a minute dose of atropine previous to the administration. There is no sign of cyanosis, and the patient's face remains a healthy colour throughout; the only restriction of oxygen is by reason of the displacement of air by ether vapour which at a maximum will be less than one-third its volume, and as in the later stages of an administration much less vapour is required the restriction becomes entirely negligible. The after-effects of ether, such as vomiting and malaise, are considerably less pronounced than following a "close" administration.

The application of the " open method to ether inhalation has been brought about by an exceedingly simple adaptation. The liquid ether is applied to a pad of open-wove fabric, such as "stock

inette" or a number of layers of absorbent gauze, stretched over a framework mask of which the margin is roughly adapted to the contours of the face; the mask rests lightly upon the face, a soft pad being interposed between its edges and the skin to prevent the entrance of air in this direction. In this way the inhaled air is made to pass through the meshes of the fabric, and in doing so every portion of it comes in close contact with the ether, and takes up a greater proportion of vapour than it would if it merely passed over the surface of the fabric, as in the ordinary way of procedure.

The induction of anaesthesia by the open method is liable to be somewhat prolonged, an undoubted disadvantage, but once full anaesthesia has been produced it is maintained without difficulty, and the results attained are in general more satisfactory than those of any other form of inhalation anaesthesia.

The intratracheal method of etherization has in recent years been in considerable requisition for special purposes. It is conducted by passing a narrow tube through the larynx into the trachea almost to the level of its bifurcation. Through this tube a continuous current of air and ether vapour is forced into the lungs at a pressure which keeps the lungs moderately distended, but not so much so as to abolish the natural respiratory movements. The air returns through the chink of the vocal cords by the side of the tube, and this continuous return blast blows away any solid or fluid particles. blood or pieces of tissue, in the neighbourhood, and prevents their entering the trachea, an accident which may possibly occur in ordinary inhalation methods. The advantage of intratracheal ether in operations involving the respiratory passages is therefore obvious; it is likewise a convenient arrangement for operations upon the face, which is left entirely uncovered; and in operations upon the interior of the thorax a proper aeration of the lungs can be thus insured.

Chloroform. The form of sudden death which is occasionally encountered under chloroform anaesthesia has acted as a deterrent to its more extended employment in spite of its manifest conveniences. An earnest endeavour was made by an influential committee appointed by the British Medical Association to find a method of preventing these chloroform deaths, by enquiring into the conditions of overdosage and devising apparatus for the precise limitation of chloroform vapour to essential requirements. The final report of this committee was issued in 1910, but the number of deaths from chloroform has remained practically undiminished since that time. An attempt has further been made to reduce the risk of overdosage by diluting the chloroform with ether in varying proportions, but this has proved to be futile as a prophylactic against death, for although the number of deaths under pure chloroform has fallen, the number under mixtures of chloroform has risen ten times in a period of ten years.

It is now becoming realized that the typical sudden chloroform fatality is not conditioned by an overdose at all. It has long been known that the majority of deaths occur in the very early stages of anaesthesia before the patient is fully narcotized, and further enquiry into reports of fatalities shows that there is generally some evidence of light anaesthesia preceding death, or else that overdosage can be ruled out of question.

There is a further point brought out by these reports, which was in fact fully appreciated by John Snow in the middle of the last century: whereas in overdose the respiration is paralyzed before the circulation, in the typical chloroform death the outstanding feature is an absolutely sudden failure of the circulation, and the failure of the respiration is a secondary result.

In 1890, Dr. Robert Kirk, boldly and with strong conviction, advanced the theory that chloroform deaths occurred from underdosage, and although his thesis was supported by important experiments, he failed to formulate an acceptable theoretical basis for it. Dr. A. G. Levy, in 1911, reported certain cases of sudden cardiac failure that he had observed in animals obviously in a light stage of chloroform anaesthesia, and he succeeded in reproducing this death by the intravenous injection of small doses of adrenalin in lightly chloroformed animals, but the experiment failed under full chloroform narcosis. This at once accounted for those cases of syncope and death, a number of which had been recorded, following the injection of adrenalin into the mucous membrane of the nose for the purposes of certain nasal operations which were always conducted under light anaesthesia, the form of this syncope being the same as in an ordinary chloroform fatality.

By following up this line of research it was shown that sudden cardiac failure could be induced likewise by various procedures-excitation of the cardiac accelerator nerves either directly or through a reflex mechanism, stimulating the excretion of the adrenal glands, by intermitting the administration of chloroform, or by withholding the chloroform during excitement and struggling; the event never occurred during deep narcosis. The underlying condition of the cardiac syncope was shown to be that of fibrillation of the ventricles, in which the ventricles are entirely deprived of their power of propelling the blood through the arteries. The seeming paradox of too small a quantity of a drug being dangerous is susceptible of explanation although the theoretical points have not been fully worked out: a relatively small proportion of chloroform renders the heart "irritable" and liable to assume a sequence of irregular beats which may pass into fibrillation, whereas a larger proportion of chloroform, by reason of its depressing effect, makes

sion or

66

stand out perpendicularly to the projectile and thus immensely increase the air resistance. Conditions are not improved by the partial breaking-off of this extension or by its incomplete formation in the gun. It is just this irregular form and size of this extenfringing" of the rotating band which makes it a possible source of great inaccuracy. Whether fringing actually takes place depends not only on the design of the band but also on the velocity of rotation of the projectile and the thinness and length of the extension formed at the rear of the band. By taking all these points into consideration it is possible to make a design which will give no trouble from fringing. But, apart from the effect of fringing, the rotating band may materially increase the resistance if improperly located. While it is desirable from other considerations to have the rotating band as near to the base of the projectile as possible, it is found that a better position for range and accuracy, even if a squarebased projectile is used, is 1/2 calibre or more from the base. Similarly, if a boat-tailed base is used, the range and accuracy are both reduced if the band is placed just at the beginning of the taper. It should be at least 1/8 calibre forward of this position.

Double and even triple rotating bands close together at the rear are sometimes used, the idea being that this construction will make the band more efficient as a gas check and that fringing is less marked than for a single rotating of the necessary width. Bands near the bourrelet have also been used. A more recent development is the use of a copper bearing band at the bourrelet. Optimum Weight of Projectile.-The question of the weight of projectile to be used with a gun of a given calibre frequently arises. Other considerations besides that of ballistics affect the answer. There is a practicable limit to the pitch of rifling, which has been fixed at about one turn in 15 calibres for low-powered guns, and one turn in 20 calibres for higher-powered guns. With some such limit in pitch of rifling, projectiles cannot be made more than about 5 calibres in total length and retain the necessary factor of stability in flight. There is thus formed a certain upper limit of length and weight. If the projectile is shortened below this limit and the weight reduced, we may assume that, with the use of a suitably quicker powder, the same muzzle energy and consequently a higher muzzle velocity may be obtained; but while the higher muzzle velocity would tend to increase the range, the smaller weight and ballistic coefficient would tend to reduce it. It is evident that for each gun there is some weight of the projectile, called the "optimum" weight, which will give the greatest range, assuming the muzzle-energy constant.

working out the maximum ranges on the basis of equal muzzle energies. Fig. 7 illustrates the maximum ranges to be expected from a 75-mm. gun under the assumption of equal muzzle energies. It is to be noted that the optimum weight increases with the muzzle energy and that the range changes only slowly as we pass from the optimum weight. In the case of large-calibre naval or coast-defence guns a reduction in weight of projectile tends toward optimum, that is, toward increase in range; but the reduced weight and increased velocity of the projectile lead to greater losses of energy in flight, resulting in a smaller striking energy at a given. range. (W. H. T.) MANUFACTURE of Shell

The material of which a projectile may be made depends largely on the functions required of it.

Cast iron is brittle, more or less hard, with low elasticity, practically no ductility, and low tenacity; consequently this material is of no value for a shell which is required to do heavy work at the end of its flight or to promote a good explosive effect, and is somewhat risky when required to stand the shock of discharge from a high-velocity gun. Cast iron, however, is fusible and easily worked, and therefore cheap; it is consequently sometimes used for practice shot with reduced propellant charges. In the World War it was used for certain chemical shell where the chemical content was liable to attack steel, and especially by the Germans-as a substitute for steel when the latter could not be had in sufficient quantities; but its use for projectiles is almost entirely confined to such. Wrought iron has a fair tenacity and a good ductility, but it is quite superseded by steel which can be manufactured as easily and cheaply.

Steel possesses the characteristics of elasticity, ductility and tenacity, and is sufficiently hard to enable it to withstand the stresses and shocks a modern projectile is required to sustain. Forged steel1 is fibrous in molecular structure, and is improved by forging, which increases the tensile strength and minimizes the chance of porous metal remaining; the more work put into the forging, the better the quality of the finished material as measured by its tensile strength in the direction of the forging. Cast steel is crystalline in molecular structure and much harder than forged steel and has less ductility and tenacity; it must always be annealed after it has been allowed to cool after casting, in order to dissipate the uneven molecular stresses set up during cooling. In the case of steel for projectiles the composition includes from 0.35% to 0.7% of carbon and small percentages of nickel, manganese, and silicon. With cast steel, the walls of a shell cannot be so thin as with forged steel because the material is not so good and there always is a risk of blow-holes and porous metal being present.

The chemical composition of the steel for shells is generally as follows:

8

The weights of similar projectiles vary with the cube of the calibre. Similar projectiles for different calibres, being the same length in calibres, are of equal stability providing the pitch of rifling is the same. The weights of the optimum projectiles vary about with the square of the calibre, if based on uniform muzzle velocities in different calibres. For high-powered guns of calibres roughly below in. the optimum weight is greater than the usually accepted weight based on similarity, and for larger calibres it is less. The optimum weight of projectile for any gun and muzzle velocity may be readily worked out by the methods of exterior

19 tons

(Light shr.) 36 tons (Heavy do.) 24 tons

24 tons

*The sulphur and phosphorus are deleterious and should be as low as possible.

† Steel for A.P. shell should have a higher percentage of carbon in order to give harder material.

1 The term "forged steel" is still used but the process of forging under a hammer has been discontinued for some time, the hydraulic press being used instead. The hydraulic press is said to work the mass more uniformly than does the hammer, while hollow-forging on a mandril has the same advantage over solid-forging. Forging should cease at a temperature of about 1,200° F., for if continued below this temperature, the metal tends to become hammer