Chap. XIII.

MACHINES , ETC.

1027

HYDROSTATIC PRESS.

pump, the piston in the air-tight cylinder will press with a power equal to 576 tons : thispower has no limits, when materials can be found strong enough to make the machine.Within the space or area of 100inches and 1 foot in height, apower equal to 500 or 600 tonsmay be easily directed againstany substance that may requirepressing, tearing up, cutting, orpulling asunder.

The operation of this press iseasily understood by supposingthe pump cylinder and connect-ing pipe b to be filled with water,and an adequate supply containedin L: when the handle of thelever H is raised, it lifts the pistonrod f which would leave a va-cuum beneath if the atmospheredid not force the water throughthe lower valve of the pump ; thelever being then pressed down,the piston rod, by descending,diminishes the capacity of thepump, which causes the lower Fig. 1567.

valve to close, and forces the water through the pipe h into the cavity of the great cylinderF, where it raises the piston D, together with the table E, a distance proportional to thequantity of water which has been injected: on the rise of the piston in the pumps, thedescent of the upper valve prevents the return of the water, and consequently the fall ofthe cylinder D. There is a discharge valve to relieve the action of the press, and whichpermits the water that escapes to pass again into the cistern at L, when the table E againdescends.

We have only described the action of a single pump, but where great power is required,a number worked by double handles are made use of; in which case particular caution isrequired to insure accuracy and to prevent leakage.

Previous to the blocks and ropes being used at the Menai bridge for hoisting the severalparts, their strength was tested by a load of 50 tons placed in a square box ; the frame wasmade of timber, the posts of whichwere 40 feet in length and 15inches square, strongly framedboth at top and bottom: twocapstans placed at a distancewere attached to the main falls,which passed through a pulleyat the bottom of the frame, bywhich means the loaded box waslifted off the ground, and everyportion effectually proved. Thetackle by which the main chainsof the bridge were hoisted to theirrespective positions was first putto the test of supporting 50 tons.

In the machines for provingthe iron work, the bar upon whichthe experiment was to be madewas secured at its two ends, inthe same manner as the blade ofa pit saw: the power was obtainedby three cogged wheels workingin as many pinions; the radius ofthe first was 1 foot 10^ inches;of the second, 2 feet 6} inches;and the largest, 3 feet inchesthe other 10-j^ inches.

The length of the bed of the machine was 12 feet 10} inches, and the diameter of theaxis of the largest wheel 8^ inches: the levers and weights that measured the strengthwere adjusted underneath the machine, the end view of which is shown.at the top of thefigure; the diameter of the cylinder was 8} inches.

3 u 2

Fig. 1568. PROVING ROVES, USED AT MENAI.

the diameter of the largest pinion was 13} inches; and