HIGH-PRESSURE ENGINE.

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low-pressure condensing engine, it is convenient to con-sider, in the first instance, its mechanism and management,and afterwards, how far it may require to be modified inorder to acquire the advantage of condensation.

The High-Pressure Non-Condensing Steam-Engine .

The elastic force of steam is a phenomenon with whichwe become acquainted very early in life. We see thatwhen water boils furiously in a kettle or caldron which iscloselyfitted byalid orcover, it has a tendency to raise itupor drive it off with considerable force ; and that the steam,collecting in the upper part of the vessel, rushes withconsiderable velocity out of any crevice or pipe whichcommunicates with the open air.

The force of the steam which is thus issuing from thespout of a kettle or crevice in the cover of a caldron iscomparatively slight; and the steam which thus rises fromboiling water is called low-pressure steam. But if westop up the spout and close the cover with accuracy, soas to confine the steam within the kettle or boiler, thewater will become hotter and hotter, and the steamstronger and stronger, until it will either force up thecover with violence, or altogether burst asunder the sidesof the boiler. In this confined and heated state thesteam acquires, from its properties, the descriptiveappellation of high-pressure steam.

Engineers are in the habit of reckoning the force ofhigh-pressure steam by a very simple expedient. Theyplace a weight such as W (Fig- 47,) upon a hole on the topof the boiler. This hole being square, and an inch in lengthand breadth, and the iveight being equal to one poundwhen the steam is strong enough just to blow the