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ing or taking a permanent set are obviated. On the other hand, air recuperators require the services of a skilled artificer for their maintenance, and as they absorb relatively a greater proportion of the recoil energy than springs a loss of pressure is likely to overload the buffer much more than a spring breakdown ; the correct charging of the system is, therefore, absolutely necessary.

The air used in recuperators must be dry and free from dust to prevent rust and abrasion; at high temperatures, moist air is the cause of pitting. An inert gas nitrogen is used by the French, and tends to preserve the " mirror " surface necessary with the cylinders. The liquid used in buffers and recuperators is usually a mixture of certain percentages of neat's foot and hydro-carbon oils, and must have certain qualities, namely, non-freezing in any climate; freedom from acid for preservation of packings, cylinders and working parts; a slight viscosity not greatly affected by con- siderable changes in temperature; non-inflammable. The buffer flow-space is designed for a specific liquid of certain viscosity, and therefore only that specified should be used. In emergency, how- ever, glycerine will serve.

Packing. Packings may be distinguished as joint-rings, soft packings, and self-tightening rings. Joint-rings copper, leather or vulcanized fibre are used with plugs, stuffing-boxes, etc. Soft packings, composed of asbestos, lead and hemp, and moulded to shape, are used in stuffing-boxes to retain liquid at normal pressures and to centre the piston-rod. Self-tightening rings, of leather or hydraulic rubber, U- or L-section, are employed to seal liquid under pressure. Frequently a combination of soft packings and self- tightening rings is used; the shock pressures are resisted by self- tightening rings whilst the soft packings prevent leakage when travelling or at rest.

Differential Recoil. This system, which dispenses with a buffer for absorbing recoil energy, has been tried by the French and Germans. In the first round the gun is hauled back against the re- cuperator by pinion and rack-gearing to the extreme recoil position, retained by a catch, loaded and laid; on releasing the catch, the gun is driven forward by the recuperator and fired by a catch when near- ing the forward position. Thus a forward movement is in progress at the moment of firing, and acts against and diminishes the recoil energy; when firing is in progress the gun is driven back by the recoil at each round. If a miss-fire occurs, the carriage would be liable to upset against the front; to obviate this, forward buffers are provided to stop the gun.

Recoil Absorbers attached to the muzzle, by which the muzzle blast is utilized to force the gun forward and thus diminish the re- sultant backward force producing recoil, were tried in 1921.

Combined Buffer and Recuperator. The system of a separate buffer and recuperator is that which normally obtains; the only known exception in which they are combined and dispense effectively with a buffer is the French 75-mm. field equipment.

The recuperator in principle a hydro-pneumatic recuperator of the floating-piston type also acts as the recoil brake, for which purpose the air-pressure must be high, about 1,200 Ib. per square inch. A guide-rod of the floating piston passes centrally through a hollow rod with pistons at either end; one is equal in size and adjacent to the floating piston, whilst the other is smaller, to work in a chamber having graduated grooves to vary the flow-space in effect, a con- trol-plunger and chamber.

The energy of recoil is absorbed by the recuperator and by the throttling of the liquid in passing through one-way valves. On recuperation, the one-way valves close and the forward movement of the floating piston forces liquid over the small piston through the graduated grooves, whence it reaches the other cylinder and reacts on the recuperator piston ; the control is provided by the decreasing flow-space due to the graduated grooves. Thus the system consists in a recuperator combined with a buffer to control the run-up only.

The energy of recoil is utilized for hydraulic power in the g-2-in. fixed mounting. Hydraulic cylinders, called compressors, are fixed to the cradle, and in them work rams which recoil with the gun. The compressors are connected with a spring accumulator by pipes filled with liquid. On firing, the liquid in the compressors is forced through the pipes and a non-return valve into the accumulator; a relief valve fitted to the accumulator acts when the latter is fully charged, the liquid then passing through the valve to a tank. On recuperation, a vacuum tends to form in the compressors, so that liquid is sucked into them from the tank through a valve and pipe in preparation for the next round. The accumulator is connected by pipes with two hydraulic hoist cylinders, the pressure to which is controlled by valves operated by levers ; and the liquid in the hoists returns through an exhaust-pipe back to the tank when the rams descend.

(F. M. R.)

(V.) TYPES OF ORDNANCE

At the beginning of the World War, the first matter that engaged the technical branches of the artillery of the fighting nations was the mobilization of all available guns. Old siege, fortress, naval and coast-defence pieces, and even modern pieces not immediately required in their existing situations, were mounted on improvised field carriages or railway mountings

and ,sent to the front. The vast increase in the production of ammunition that soon became necessary was at first an adminis- trative rather than a technical question. As the war progressed, new material and new designs were required to meet the exi- gencies that arose. The development of artillery material dur- ing and after the war came under two principal headings: (a) simplification in design of existing equipments and ammuni- tion to admit of mass production; (b) design and production of new equipments to meet the altered conditions of warfare.

A gun equipment of 1914 was a highly specialized engineering product. The cost of the gun was small relatively to that of the personnel of the army, and it was possible to spend time, labour and money on producing an ideal machine in which every ounce of weight should serve a useful purpose. Expensive materials such as high-grade steel and bronze were freely used without regard to any possible difficulty in procuring them during a long war, and complicated designs such as that of the bronze cradle of the British i8-pdr. were adopted without con- sidering the difficulties of mass production.

In every country, when vast quantities of guns and ammuni- tion had to be made, and when non-military factories had to be turned into arsenals, the first task of the technical branches of the artillery was to simplify and standardize designs. Common steel, of stouter section, was used in place of high-grade steel; cast iron replaced brass where possible, and rigid limitations of weight were relaxed. The general result was a relatively simple and almost clumsy design, easy to manufacture, highly finished in essential parts only, and capable of rough usage.

The alterations in the design of existing guns, other than those intended to facilitate manufacture, were mostly directed towards obtaining longer range, the main reason for this being the increase in depth of a system of defences from a single trench line to a series of defensive zones several miles deep. The Germans met the situation boldly, in spite of their manufacturing difficulties, by the issue of a new long barrel for their field-gun equipment, and an upper carriage which enabled elevation up to 40 to be given. Similarly they lengthened the light field howitzer, the 4-in. medium gun, and the 6-in. gun. Their heavier natures did not lend themselves to conversion, and new equipments had to be designed. However, streamline shell (see AMMUNITION) were issued which enabled longer ranges to be obtained. The French bent the trail of their field gun to allow a few degrees more elevation. They had only 105 field howitzers, so these had to be manufactured. They met the shortage of long-range howitzers by using old guns bored out to 8-in. cal. and mounted on high-angle carriages as howitzers. The British improved the carriage of the i8-pdr. field gun and issued a new 6-in. howitzer. The British army had no heavy guns or howitzers except those mounted for coast defence, and the heavy guns for the war were at first taken from the navy.

New Equipments made during the War. Speaking generally, these were neither novel nor original. There was no time to test new ideas, and artillery authorities fell back on old and approved designs, modified in the direction of greater power (at the expense of lightness) and simph'city of manufacture. Even the British i8-pdr. Mark IV. field gun, which looked very different from its predecessor, was only a reversion to established Continental practice. The German " 75-mile " gun was not a new design, though it came as a surprise to laymen and even to most artillerists. Before the war, artillery scientists had advocated a new system of differential recoil, known in different countries as the dynamic cradle, the canon lance, and the Vorlaufgeschiltz. In this system a Q.F. gun was fired while in rapid forward motion under the impulse of the recuperator, thus reducing its recoil-energy so that a much lighter carriage could be used. Although a French mountain gun of this type already existed, this new system was not even tried in any of the equipments brought out during the war, and complications such as the automatic and semi-automatic breech-mechanisms gave place to simplicity and " fool-proof " gear.

Post-War Equipments. All the nations which took part in the war have now a complete armament of guns, and none of