Rensselaer Republican, Volume 17, Number 11, Rensselaer, Jasper County, 20 November 1884 — Atmospheric Pressure on Boiling Liquids. [ARTICLE]

Atmospheric Pressure on Boiling Liquids.

“We find that in boiling cane sap it will evaporate more rapidly in the night, or in a cloudy day, than in a sunshiny day. Why is this ?” The difference, given a uniform heat, must be caused by varying atmospheric pressures. The boiling point is lower on the summit of a mountain than at its base--that is, liquids boil there with less heat and evaporate more rapidly while boiling, because the pressure of the atmosphere there is less, or, as we usually say, the air is lighter. Now the pressure of the atmosphere is less on a cloudy than on a bright day, as is shown by the falling barometer, but is not always less at night. Usually in our climate and latitude the barometer has its highest average at about 9 a. m. and 9p. m. In continued fine weather it often stands at the same height during the afternoon, and its fall, even during the last half of the night, is but slight. Close observation of the boiling sap, therefore, with reference to the barometer fluctuations, would readily solve the mystery of its greater or less evaporation.— Inter Ocean.