. The Ontario high school physics. Fio. 280.—Boiling point of aliquid lowered by decrease ofpressure. be repeated several times,the air at the beginning, the water maybe made to boil even when the temperatureis reduced to that of the room. The reason why the boiling point dependsupon the pressure is readily found. Bubblesof vapour begin to form in the liquid onlywhen the pressure exerted by the vapourwithin the bubble balances the pressure onthe surface of the liquid (Fig. 281). Werethe pressure in the bubble less, the bubblewould collapse. But the pressure of avapour in contact with its liqui
. The Ontario high school physics. Fio. 280.—Boiling point of aliquid lowered by decrease ofpressure. be repeated several times,the air at the beginning, the water maybe made to boil even when the temperatureis reduced to that of the room. The reason why the boiling point dependsupon the pressure is readily found. Bubblesof vapour begin to form in the liquid onlywhen the pressure exerted by the vapourwithin the bubble balances the pressure onthe surface of the liquid (Fig. 281). Werethe pressure in the bubble less, the bubblewould collapse. But the pressure of avapour in contact with its liquid in anenclosed space varies with the temperature. Fig. 281. —Balance be-tween external pres-sure of the air and thepressure exerted bythe vapour within abubble. Hence, a liquid EFFECT OF PRESSURE ON THE BOILING POINT 253 will be upon tlic point of boiling when its temperature has risensufficiently lii(i,h for the pressure of the saturated vapour ofthe liquid to Ijo e([ual to the pressure sustained by the surfaceof the li(j[uid. Therefore, when the pressure on the surface ishigh, the boiling point must be high, and vice versa. The 240230 ezozoo 190160 no ISO150140130IZO no 10090 ^ ^ ^ / / 1 / ^ / / / g / ^ it / ^ / ■^ / / / pt f5. UR 11^ Al MO: iPH -M S Fig. 282.—Curve showing the relation between the pressure and the boiling point of water. accompanying diagram (Fig. 282) shows graphically the rela-tion between the pressure and the boiling point of water,ranging from 1 to 25 atmospheres. It is to be noted that the steam bubbles begin in the smallair or gas bubbles present in the water, and when these areremoved by prolonged boi
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