Kingdom.] RAILWAY AND MARINE MECHANISM. 220

North Areas A. 13. 10 to 34; 0. D. E, 1 to 10, & 19 to 33 ; F. 1 to 32; G. II. 1 to 13, & 19 to 2G.

G G G G—Clamps.

H—Chains.

11—Guide rods, wrought iron.

IC—Guide rod beam.

L L—Valves.

M—Distance pieces between wrought-iron Sandwichgirders.

Fig . I. represents a front elevation of the press;Fig. II. an end elevation; and Fig . III. shows its applica-tion in raising the Britannia tube, with the latter partlylifted.

The internal diameter of the cylinder is 22 inches, thediameter of the ram is 20 inches, the external diameter ofthe cylinder is 42 inches, external length 9 feet 1A inch;thickness of metal 10 inches; the water is forced into thecylinder through a pipe and valve L, the press is placedin the jacket C, and rests upon the cast-iron beams B B,which again are supported by the wrought-iron beamsA A; the cast-iron crosshead F has wrought-iron links letin at the top, for the purpose of strengthening the partsubject to tensile strain; the sides of the jacket also arestrengthened with wrought-iron slabs, weighing 30 cwt.each, expanded first by heat and then fitted-on hot, andallowed to contract. To cast the cylinder, it required 22tons of fluid metal, the additional quantity beyond itsfinished weight being required for the head, or git, whichweighed 2^ tons. This head, or git, was kept in a fluidstate for six hours after the run, by replacing the materialafter it became stiff, with metal fresh from the furnace,and of the highest attainable temperature, for the purposeof supplying the space in this immense body of metalbelow, consequent upon the contraction. In three daysafterwards the cylinder was partly denuded of its outercoat of sand, when it was found red hot: in seven daysit was lifted from the pit in which it was cast, and inten days, or 240 hours, it was sufficiently cool to beapproached by men well inured to heat, for the purposeof dressing the remaining sand off it.

. The A A beams, for supporting the press, consisted ofsix vertical ribs of boiler plates, f-tlis thick, united byvertical strips, to preserve them in form ; the 2| inchspaces between ribs were filled with American elm, sothat the vertical rib was a sandwich of elm and iron.The top and bottom flanges were each formed by twelvewrought-iron bars, extending the whole length of beam.The top bars 7 inches wide, and the bottom bars 9 inchesby 1J inch; the whole riveted together. The weight ofeach girder was 12 tons. In order to prevent the crushingat the ends, cast-iron plates were inserted instead of thewood.

The weight actually supported by one pair of beamswas 1,177 tons, but they were capable of sustaining2,000 tons. The length between the bearing was 17 feet4 inches. The ram was cast hollow and turned to bedtruly, beneath the crosshead, which was bored to receiveit. The crosshead was guided by two wrought-iron rods,6 inches diameter, fitted in sockets on the top of thepress, and keyed above into a cast-iron girder, K, built inthe masonry.

There were two sets of clamps: the one placed on thecrosshead, and rising with it, was immediately used forlifting the chain and tube; the under set was fixed on thecast-iron girders which support the press, and was usedfor securing the chain at the end of each lift, while thepress was lowered, and the upper set of links removed; theyare in all respects similar to each other. The wrought-iron clamping cheeks are slotted to fit closely beneath theslotted shoulder in the head of the links; they arewithdrawn or closed by right and left-handed screws, onturning which the cheeks recede from each other, or aredrawn into close contact with the chain. To insure aparallel action, the screws are moved simultaneouslyby a winch and gearing; they are thus easily worked byone man. Thus at each stroke of the press the tube wasraised 6 feet, the time occupied in one lift being usuallyfrom 30 to 45 minutes.

The lifting chains were manufactured by Messrs. Howard& Ravenhill; the clamps and valves by Messrs. Easton &Amos. The superintendence of the designs and con-

struction of this machinery were entrusted by Mr. RobertStephenson, the engineer , to Mr. Edwin Clark.

The greatest weight lifted by the press at the Britanniabridge was 1,144 tons; the quantity of water used for eacli6 feet lift 81 £ gallons. “The pressure at 3 tons pel-circular inch equals 3'819 tons per square inch, whichwould raise a column of water 5-41 miles in height; thispressure would, therefore, be sufficient to throw waterover the highest mountains on the globe.” This extra-ordinary fact is derived from Mr. Edwin Clark’s work onthe Britannia and Conway bridges. The following addi-tional extract shows indirectly the vast power of thismachine:—

“ If it were required that 1 lb. should raise the tube, or2,000 tons, then one arm of the lever must be 448,000times as long as the other; but if the 1 lb. move througha space of l inch, the tube will be only lifted th partof an inch; and in order to raise the tube 100 feet thepressure of 1 lb. must be continued through a space •of 83,522 miles; and, conversely, a pressure of 2,000 tonsthrough a space of 100 feet, would raise 1 lb. 83,522miles; thus the descent of a clock-weight through a spaceof 6 feet overcomes the friction of the machine, andmoves the extremity of an ordinary seconds-hand througha space of two miles in a week, and the descent of thetube to the water would maintain the going of an ordinaryclock for 240,000 years,” or the power expended by thepress in lifting the tube 100 feet, if applied to an ordinaryclock, would work it for a period of 240,000 years.

After the first tube was raised, the cylinder met withan accident, described in the following terms by Mr.Clark:—

“ In a little more than a fortnight after this operationthe presses were removed ready for raising the next tube.They were lowered and raised again by means of capstans,with an 8-inch rope; and in this operation anotheraccident occurred with the unlucky press. The cylinderwas lowered from a cat-head at the top of the tower;the rope from the blocks led to a capstan on the beach,on which three turns only were taken; while the cylinder,weighing 15 tons, was suspended at an elevation of 140feet above the water, the rope unexpectedly surged onthe capstan, and was dragged out of the hands of the menwho were holding it; the cylinder descended with fearfulvelocity, dragging the rope through the block tackle andround the capstan, which fortunately became palled bythe jerk. As the velocity increased, the cat-head in thetower gave way, and the cylinder fell on the stone shelfbelow, fracturing the masonry, and gliding off 50 or 60feet into the Straits. Several men were injured, and asailor who was serving out the coil of rope was draggedround the capstan and killed. None of the tackle wasbroken, and the press was easily raised by the ropesattached to it, and was found to be uninjured by thefall.”

[The weight raised by this single press at the Britanniabridge was 1,144 tons, and this was effected with easeby the hydraulic press exhibited. A popular error pre-vails on the subject of gaining power by the applicationof machinery, and particularly with relation to the hy-draulic press, in which it appears that a small appliedforce produces immense results. In this case, however,as in all others, the power is only transferred anddistributed. Water, and indeed all fluids, possess theproperty of pressing equally in all directions. If wateris enclosed in an iron box, and the force of one pound isapplied to but one square inch of its surface, this pres-sure is at once communicated to every square inch ofthe surface of the box. Bramah rendered this force avail-able by applying a packing around the moving pistons,which made them perfectly water-tight under any pres-sure. By the force pump, pressure is applied to thewater in the small cylinder of the pump, and this fluidbeing connected with that in the large cylinder of thepress, whatever force is applied to the water in the first,