SHOP TOOLS.

97

pressure which is applied to it. The element of time in theseoperations has been proved incontestably to be an importantfactor in the changes of form which are produced in metalswhen being manipulated. That is to say, the continuity in thefibres of the metal is better produced by a slow blow or squeeze,than when the Operation is performed more rapidly, as is thecase with a sharp blow.

The application of hydraulic power at high pressures toactuate machines to produce the results thus indicated, hasopened out a wide field for the extension of its employment.The important part that hydraulic power will play in the futuremanipulation of iron and steel justifies a somewhat lengthyreference being made to this brauch of the subjeet.

The employment of hydraulic pressure to workshop toolsdates as far back as Bramah ’s time, a hydraulic planing machinehaving been then erected at Woolwich, in which many of theoperations of the tool were performed by water-pressure. Morerecently (about thirty years ago) a direct-acting hydraulic slot-ting machine was at work for some years at Elswick. It hada stroke of about 4 feet, with a tumbling weight to reverse theaction, and it was W'orked with an accumulator pressure of 700lbs. per square inch. It was placed vertically upon girderssupported by pillars 16 feet apart, thus enabling large piecesof machinery to be easily slotted.

Hydraulic power is now generally applied at high pressureto actuate shop tools. The installations that are now laid outto work an extensive series of appliances, may be regarded ascomplete Systems of producing, storing, and distributing water-power at the high pressure of 1500 lbs. in the same way thatSir William Armstrong perfected the original System of hydraulicpower distribution, and utilisation, for the multifarious purposesto which it has been, and still is, applied at the lower pressureof 600 or 700 lbs. to the square inch. In both cases the machinesto which the power is most advantageously applied are directacting, and the work to be performed is intermittent.

The adoption of a pressure of 1500 lbs. per square inch