A text-book on chemistry : for the use of schools and colleges . sibility of vapor, the high-pressure engine on its elastic force. Fig. 31. The principle involved in the action of the low-pressure engine, and more espe-cially that form of it which was the inven-tion of Newcomen, is well illustrated bythe instrument represented in Fig. 31. Itconsists of a glass tube, blown into a bulbat its lower extremity. In the bulb somewater is placed, and a piston slides, with-out leakage, in the tube. On holding thebulb in the flame of a spirit lamp, steam isgenerated, and the piston forced dipp
A text-book on chemistry : for the use of schools and colleges . sibility of vapor, the high-pressure engine on its elastic force. Fig. 31. The principle involved in the action of the low-pressure engine, and more espe-cially that form of it which was the inven-tion of Newcomen, is well illustrated bythe instrument represented in Fig. 31. Itconsists of a glass tube, blown into a bulbat its lower extremity. In the bulb somewater is placed, and a piston slides, with-out leakage, in the tube. On holding thebulb in the flame of a spirit lamp, steam isgenerated, and the piston forced dipping it into a basin of cold water,the steam condenses and the piston is de-pressed ; and this action may be repeatedat pleasure. As the pressure of the atmosphere determines the boil-ing point of a liquid, and as that pressure is variable, theboiling point is not a fixed, but a variable point. Thereare many experiments which might be introduced as proofsof this fact. If a glass of warm water be placed beneaththe receiver of an air pump, as in Fig. 32, when the. Give an example of the rapidity of its condensation. On what proper-ty of vapor does the low-pressure steam-engine depend 1 On what, thehigh-pressure ? How may it be proved that the boiling point depends onthe pressure ? BOILING IN VACUO. 47
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