Εικόνες σελίδας
PDF
Ηλεκτρ. έκδοση

PRACTICAL EXAMINATOR

ON

STEAM AND THE STEAM-ENGINE.

1. What amount of elementary knowledge, independent of practical qualifications, is necessary to constitute an individual a practical engineer?

In the construction or practical working of a steam-engine, the elementary requirements are diversified; but the most necessitous are a knowledge of the properties of steam, and the principles of the steam-engine relative thereto.

2. What is steam?

Steam, generally, is the aqueous vapour arising from water at any degree of temperature; but steam, available as a motive power, is the vapour produced from water when heated to 212° Fah.

and upwards.

3. Why designate steam an aqueous vapour? First, because it is produced from aqua, or water, combined with heat; and second, in order to distinguish it from that of a gas: the properties of the latter being those of retaining permanently the aeriform state, unless liquefied by compression; while the aeriform state of the former cannot be retained unless at a uniform temperature, and in contact with the water from which it was generated.

4. What are degrees of temperature?

By degrees of temperature is understood the quantity of sensible heat in steam, water, air, &c., as indicated by the expansion or rise of the mercury in the tube of a thermometer.

5. What is a thermometer?

An instrument founded on the properties which heat possesses of expanding all bodies, the degrees of temperature being measured by the contractions and expansions of a column of mercury, the heat of boiling and freezing water being regarded as two fixed points, and the space between them divided into a certain number of equal parts.

Fahrenheit's scale; the freezing point of fresh water is 32°, and the boiling point 212°.

6. Is steam, and the water from which it is generated, of equal temperatures while they remain in immediate contact?

Yes; and under such circumstances designated common steam, and of low pressure if not exceeding fifteen pounds per square inch above that of atmospheric pressure; or high-pressure steam when exceeding that density.

7. Why make the distinction common steam? Because, when steam is separated by another vessel from its water of formation, it may be subjected to a greater degree of heat, whereby the watery particles of which it is composed are diminished in bulk, but augmented in quantity and elastic force, through excess of caloric, and commonly termed superheated steam.

8. What is meant by steam being available as a motive power?

Steam being available as a motive power, signifies that its inherent force or power is so great as to cause useful motion to machinery through the medium of the steam-engine.

« ΠροηγούμενηΣυνέχεια »