Thickness of Hydraulic Cylinders.-From a table used by Sir W. G. Armstrong we take the following, for cast-iron cylinders, for an interior pressure of 1000 lbs. per square inch: Diam. of cylinder, inches.. 2 4 6 8 10 12 16 20 24 Thickness, inches... 0.832 1.146 1.552 1.875 2.222 2.578 3.19 3.69 4.11 For any other pressure multiply by the ratio of that pressure to 1000. These figures correspond nearly to the formula t=0.175d+0.48, in which t = thickness and d = diameter in inches, up to 16 inches diameter, but for 20 inches diameter the addition 0.48 is reduced to 0.19 and at 24 inches it disappears. For formulæ for thick cylinders see page 287, ante.

Cast iron should not be used for pressures exceeding 2000 lbs. per square inch. For higher pressures steel castings or forged steel should be used. For working pressures of 750 lbs. per square inch the test pressure should be 2500 lbs. per square inch, and for 1500 lbs. the test pressure should not be less than 3500 lbs.

Speed of Hoisting by Hydraulic Pressure. The maximum allowable speed for warehouse cranes is 6 feet per second; for platform cranes 4 feet per second; for passenger and wagon hoists, heavy loads, 2 feet per second. The maximum speed under any circumstances should never exceed 10 feet per second.

The Speed of Water Through Valves should never be greater than 100 feet per second.

Speed of Water Through Pipes.-Experiments on water at 1600 lbs. pressure per square inch flowing into a flanging-machine ram, 20-inch diameter, through a 6-inch pipe contracted at one point to 4-inch, gave a velocity of 114 feet per second in the pipe, and 456 feet at the reduced section. Through a 1⁄4-inch pipe reduced to 3-inch at one point the velocity was 213 feet per second in the pipe and 381 feet at the reduced section In a 2-inch pipe without contraction the velocity was 355 feet per second.

For many of the above notes the author is indebted to Mr. John Platt, consulting engineer, of New York.

High-pressure Hydraulic Presses in Iron-works are described by R. M. Daelen, of Germany, in Trans. A. I. M. E. 1892. The following distinct arrangements used in different systems of high-pressure hydraulic work are discussed and illustrated:

1. Steam-pump, with fly-wheel and accumulator.

2. Steam-pump, without fly-wheel and with accumulator.

3. Steam-pump, without fly-wheel and without accumulator.

In these three systems the valve-motion of the working press is operated In the high-pressure column. This is avoided in the following:

4. Single-acting steam-intensifier without accumulator.

5. Steam-pump with fly-wheel, without accumulator and with pipe-circuit. 6. Steam-pump with fly-wheel, without accumulator and without pipecircuit.

The disadvantages of accumulators are thus stated: The weighted plungers which formerly served in most cases as accumulators, cause violent shocks in the pipe-line when changes take place in the movement of the water, so that in many places, in order to avoid bursting from this cause, the pipes are made exclusively of forged and bored steel. The seats and cones of the metallic valves are cut by the water (at high speed), and in such cases only the most careful maintenance can prevent great losses of power.

Hydraulic Power in London.-The general principle involved is pumping water into mains laid in the streets, from which service-pipes are carried into the houses to work lifts or three-cylinder motors when rotatory power is required. In some cases a small Pelton wheel has been tried, working under a pressure of over 700 lbs. on the square inch. Over 55 miles of hydraulic mains are at present laid (1892).

The reservoir of power consists of capacious accumulators, loaded to a pressure of 800 lbs. per square inch, thus producing the same effect as if large supply-tanks were placed at 1700 feet above the street-level. The water is taken from the Thames or from wells, and all sediment is removed therefrom by filtration before it reaches the main engine-pumps.

There are over 1750 machines at work, and the supply is about 6,500,000 gallons per week.

It is essential that the water used should be clean. The storage-tank extends over the whole boiler-house and coal-store. The tank is divided, and a certain amount of mud is deposited here. It then passes through the sur face condenser of the engines, and it is turned into a set of filters, eight in number. The body of the filter is a cast-iron cylinder, containing a layer of

granular filtering material resting upon a false bottom; under this is the distributing arrangement, affording passage for the air, and under this the real bottom of the tank. The dirty water is supplied to the filters from an overhead tank. After passing through the filters the clean effluent is pumped into the clean-water tank, from which the pumping-engines derive their supply. The cleaning of the filters, which is done at intervals of 24 hours, is effected so thoroughly in situ that the filtering material never requires to be removed.

The engine-house contains six sets of triple-expansion engines. The cylinders are 15-inch, 22-inch, 36 inch × 24-inch. Each cylinder drives a single plunger-pump with a 5-inch ram, secured directly to the cross-head, the connecting-rod being double to clear the pump. The boiler-pressure is 150 lbs. on the square inch. Each pump will deliver 300 gallons of water per minute under a pressure of 800 lbs. to the square inch, the engines making about 61 revolutions per minute. This is a high velocity, considering the heavy pressure; but the valves work silently and without perceptible shock. The consumption of steam is 14.1 pounds per horse per hour.

The water delivered from the main pumps passes into the accumulators. The rams are 20 inches in diameter, and have a stroke of 23 feet. They are each loaded with 110 tons of slag, contained in a wrought-iron cylindrical box suspended from a cross-head on the top of the ram.

One of the accumulators is loaded a little more heavily than the other, so that they rise and fall successively; the more heavily loaded actuates a stop. valve on the main steam-pipe. If the engines supply more water than is wanted, the lighter of the two rams first rises as far as it can go; the other then ascends, and when it has nearly reached the top, shuts off steam and checks the supply of water automatically.

The mains in the public streets are so constructed and laid as to be perfectly trustworthy and free from leakage.

Every pipe and valve used throughout the system is tested to 2500 lbs. per square inch before being placed on the ground and again tested to a reduced pressure in the trenches to insure the perfect tightness of the joints. The jointing material used is gutta-percha.

The average rate obtained by the company is about 3 shillings per thou sand gallons. The principal use of the power is for intermittent work in cases where direct pressure can be employed, as, for instance, passenger elevators, cranes, presses, warehouse hoists, etc.

An important use of the hydraulic power is its application to the extinguishing of fire by means of Greathead's injector hydrant. By the use of these hydrants a continuous fire-engine is available.

Hydraulic Riveting-machines.-Hydraulic riveting was introduced in England by Mr. R. H. Tweddell. Fixed riveters were first used about 1868. Portable riveting-machines were introduced in 1872.

The riveting of the large steel plates in the Forth Bridge was done by small portable machines working with a pressure of 1000 lbs. per square inch. In exceptional cases 3 tons per inch was used. (Proc. Inst. M. E., May, 1889.) An application of hydraulic pressure invented by Andrew Higginson, of Liverpool, dispenses with the necessity of accumulators. It consists of a three-throw pump driven by shafting or worked by steam, and depends partially upon the work accumulated in a heavy fly-wheel. The water in its passage from the pumps and back to them is in constant circulation at a very feeble pressure, requiring a minimum of power to preserve the tube of water ready for action at the desired moment, when by the use of a tap the current is stopped from going back to the pumps, and is thrown upon the piston of the tool to be set in motion. The water is now confined, and the driving-belt or steam-engine, supplemented by the momentum of the heavy fly-wheel, is employed in closing up the rivet, or bending or forging the object subjected to its operation.

Hydraulic Forging.-In the production of heavy forgings from cast ingots of mild steel it is essential that the mass of metal should be operated on as equally as possible throughout its entire thickness. When employing a steam-hammer for this purpose it has been found that the external surface of the ingot absorbs a large proportion of the sudden impact of the blow, and that a comparatively small effect only is produced on the central portions of the ingot, owing to the resistance offered by the inertia of the mass to the rapid motion of the falling hammer-a disadvantage that is entirely overcome by the slow, though powerful, compression of the hydraulic forging-press, which appears destined to supersede the steamhammer for the production of massive steel forgings.

In the Allen forging-press the force-pump and the large or main cylinder of the press are in direct and constant communication. There are no intermediate valves of any kind, nor has the pump any clack-valves, but it simply forces its cylinder full of water direct into the cylinder of the press, and receives the same water, as it were, back again on the return stroke. Thus, when both cylinders and the pipe connecting them are full, the large ram of the press rises and falls simultaneously with each stroke of the pump, keeping up a continuous oscillating motion, the ram, of course, travelling the shorter distance, owing to the larger capacity of the press cylinder. (Journal Iron and Steel Institute, 1891. See also illustrated article In Modern Mechanism," page 668.)

For a very complete illustrated account of the development of the hy draulic forging-press, see a paper by R. H. Tweddell in Proc. Inst. C. E., vol. cxvii. 1893-4.

Hydraulic Forging-press.-A 2000-ton forging-press erected at the Couillet forges in Belgium is described in Eng. and M. Jour., Nov. 25, 1893. The press is composed essentially of two parts-the press itself and the compressor. The compressor is formed of a vertical steam-cylinder and a hydraulic cylinder. The piston-rod of the former forms the piston of the latter. The hydraulic piston discharges the water into the press proper. The distribution is made by a cylindrical balanced valve; as soon as the pressure is released the steam-piston falls automatically under the action of gravity. During its descent the steam passes to the other face of the piston to reheat the cylinder, and finally escapes from the upper end.

When steam enters under the piston of the compressor-cylinder the piston rises, and its rod forces the water into the press proper. The pressure thus exerted on the piston of the latter is transmitted through a cross-head to the forging which is upon the anvil. To raise the cross-head two small single-acting steam-cylinders are used, their piston-rods being connected to the cross-head; steam acts only on the pistons of these cylinders from below. The admission of steam to the cylinders, which stand on top of the press frame, is regulated by the same lever which directs the motions of the compressor. The movement given to the dies is sufficient for all the ordinary purposes of forging.

A speed of 30 blows per minute has been attained. A double press on the same system, having two compressors and giving a maximum pressure of 6000 tons, has been erected in the Krupp works, at Essen.

The Aiken Intensifier. (Iron Age, Aug. 1890.)-The object of the machine is to increase the pressure obtained by the ordinary accumulator which is necessary to operate powerful hydraulic machines requiring very high pressures, without increasing the pressure carried in the accumulator and the general hydraulic system.

The Aiken Intensifier consists of one outer stationary cylinder and one inner cylinder which moves in the outer cylinder and on a fixed or stationary hollow plunger. When operated in connection with the hydraulic bloomshear the method of working is as follows: The inner cylinder having been filled with water and connected through the hollow plunger with the hydrau lic cylinder of the shear, water at the ordinary accumulator-pressure is admitted into the outer cylinder, which being four times the sectional area of the plunger gives a pressure in the inner cylinder and shear cylinder connected therewith of four times the accumulator-pressure-that is, if the accumulator-pressure is 500 lbs. per square inch the pressure in the intensifier will be 2000 lbs. per square inch.

Hydraulic Engine driving an Air-compressor and a Forging-hammer. (Iron Age, May 12, 1892.)-The great hammer in Terni, near Rome, is one of the largest in existence. Its falling weight amounts to 100 tons, and the foundation belonging to it consists of a block of cast iron of 1000 tons. The stroke is 16 feet 434 inches; the diameter of the cylinder 6 feet 3 inches; diameter of piston-rod 1334 inches; total height of the hammer, 62 feet 4 inches. The power to work the hammer, as well as the two cranes of 100 and 150 tons respectively, and other auxiliary appliances belonging to it, is furnished by four air-compressors coupled together and driven directly by water-pressure engines, by means of which the air is compressed to 73.5 pounds per square inch. The cylinders of the waterpressure engines, which are provided with a bronze lining, have a 1334-inch bore. The stroke is 4734 inches, with a pressure of water on the piston amounting to 264.6 pounds per square inch. The compressors are bored out to 311⁄2 inches diameter, and have 4734-inch stroke. Each of the four cylin ders requires a power equal to 280 horse-power. The compressed air is de.

livered into huge reservoirs, where a uniform pressure is kept up by means of a suitable water-column.'

The Hydraulic Forging Plant at Bethlehem, Pa., is described in a paper by R. W. Davenport, read before the Society of Naval Engineers and Marine Architects, 1893. It includes two hydraulic forging. presses complete, with engines and pumps, one of 1500 and one of 4500 tons capacity, together with two Whitworth hydraulic travelling forging-cranes and other necessary appliances for each press; and a complete fluid-compres sion plant, including a press of 7000 tons capacity and a 125 ton hydraulic travelling crane for serving it (the upper and lower heads of this press weighing respectively about 135 and 120 tons).

A new forging-press has been designed by Mr. John Fritz, for the Bethlehem Works, of 14,000 tons capacity, to be run by engines and pumps of 15,000 horse power. The plant is served by four open-hearth steel furnaces of a united capacity of 120 tons of steel per heat.

Some References on Hydraulic Transmission.-Reuleaux's "Constructor;" "Hydraulic Motors, Turbines, and Pressure-engines," G. Bodmer, London, 1889; Robinson's "Hydraulic Power and Hydraulic Machinery," London, 1888; Colyer's "Hydraulic Steam, and Hand-power Lifting and Pressing Machinery," London, 1881. See also Engineering (London), Aug. 1, 1884, p. 99, March 13, 1885, p. 262; May 22 and June 5, 1891, pp. 612, 665; Feb. 19, 1892, p. 25; Feb. 10, 1893, p. 170.

FUEL.

Theory of Combustion of Solid Fuel. From Rankine, somewhat altered.)-The ingredients of every kind of fuel commonly used may be thus classed: (1) Fixed or free carbon, which is left in the form of charcoal or coke after the volatile ingredients of the fuel have been distilled away. These ingredients burn either wholly in the solid state (C to CO2), or part in the solid state and part in the gaseous state (CO+O = CO2), the lat ter part being first dissolved by previously formed carbonic acid by the re action CO2+C=2C0. Carbonic oxide, CO, is produced when the supply of air to the fire is insufficient.

(2) Hydrocarbons, such as olefiant gas, pitch, tar, naphtha, etc., all of which must pass into the gaseous state before being burned.

If mixed on their first issuing from amongst the burning carbon with a large quantity of hot air, these inflammable gases are completely burned with a transparent blue flame, producing carbonic acid and steam. When mixed with cold air they are apt to be chilled and pass off unburned. When raised to a red heat, or thereabouts, before being mixed with a sufficient quantity of air for perfect combustion, they disengage carbon in fine pow der, and pass to the condition partly of marsh gas, and partly of free hydrogen; and the higher the temperature, the greater is the proportion of carbon thus disengaged.

If the disengaged carbon is cooled below the temperature of ignition be fore coming in contact with oxygen, it constitutes, while floating in the gas, smoke, and when deposited on solid bodies, soot.

But if the disengaged carbon is maintained at the temperature of ignition and supplied with oxygen sufficient for its combustion, it burns while float ing in the inflammable gas, and forms red, yellow, or white flame. The flame from fuel is the larger the more slowly its combustion is effected. The flame itself is apt to be chilled by radiation, as into the heating surface of a steam-boiler, so that the combustion is not completed, and part of the gas and smoke pass off unburned.

(3) Oxygen or hydrogen either actually forming water, or existing in combination with the other constituents in the proportions which form water. Such quantities of oxygen and hydrogen are to left be out of account in determining the heat generated by the combustion. If the quantity of water actually or virtually present in each pound of fuel is so great as to make its latent heat of evaporation worth considering, that heat is to be deducted from the total heat of combustion of the fuel.

(4) Nitrogen, either free or in combination with other constituents. This substance is simply inert.

(5) Sulphuret of iron, which exists in coal and is detrimental, as tending to cause spontaneous combustion.

(6) Other mineral compounds of various kinds, which are also inert, and form the ash left after complete combustion of the fuel, and also the rlinker or glassy material produced by fusion of the ash, which tends to choxe the grate.

Total Heat of Combustion of Fuels. (Rankine.) The following table shows the total heat of combustion with.oxygen of one pound of each of the substances named in it, in British thermal units, and also in Ibs. of water evaporated from 212°. It also shows the weight of oxygen required to combine with each pound of the combustible and the weight of air necessary in order to supply that oxygen. The quantities of heat are given on the authority of MM. Favre and Silbermann.

The imperfect combustion of carbon, making carbonic 'oxide, produces less than one third of the heat which is yielded by the complete combustion. The total heat of combustion of any compound of hydrogen and carbon is nearly the sum of the quantities of heat which the constituents would produce separately by their combustion. (Marsh-gas is an exception.)

In computing the total heat of combustion of compounds containing oxy. gen as well as hydrogen and carbon, the following principle is to be observed: When hydrogen and oxygen exist in a compound in the proper proportion to form water (that is, by weight one part of hydrogen to eight of oxygen), these constituents have no effect on the total heat of combustion. If hydrogen exists in a greater proportion, only the surplus of hydrogen above that which is required by the oxygen is to be taken into account. The following is a general formula (Dulong's) for the total heat of combustion of any compound of carbon, hydrogen, and oxygen:

Let C, H, and O be the fractions of one pound of the compound, which consists respectively of carbon, hydrogen, and oxygen, the remainder being nitrogen, ash, and other impurities. Let h be the total heat of combustion of one pound of the compound in British thermal units. Then

h = 14,500 {C+4.28(H)}.

The following table shows the composition of those compounds which are of importance, either as furnishing oxygen for combustion, as entering into the composition, or as being produced by the combustion of fuel: