Boiling

Boiling, or ebullition, signifies the transition of a substance from the liquid to the gaseous state. As the temperature of the liquid rises, its particles as a rule exhibit a greater inclination for free motion, till at last a temperature is reached when the vapour pressure within the liquid is sufficiently great to overcome the external pressure. This temperature is called the boiling-point of the liquid at that particular pressure. Bubbles of vapour then begin to form in the liquid; they pass to the surface unless cooled by transit through colder layers of the liquid, and are given off as gas into the air. It is evident that the temperature at which this takes place must depend on the external pressure, the one increasing with the other. Thus, water at 1/2 atmosphere pressure boils at 82° C, a fact that may be verified by placing a vessel of water at this temperature within the receiver of an air-pump, and gradually diminishing the pressure therein. Water under 1 atmosphere pressure boils at 100° C. or 212° F.; and under 2 atmospheres, at 120° C. The connection between the boiling-point and pressure is known accurately for water by experiments of Regnault. Thus, by determining the boiling-point of water we can estimate the external pressure, a principle employed for the measurement of heights by the hypsometer (q.v.).

The following are the boiling-points of the more important liquids: -

Sulphurous anhydride - 8.00 C
Ether - 34.80 C
Carbon bisulphide - 48.05 C
Acetone - 56.28 C
Bromine - 63.00 C
Wood-spirit - 65.50 C
Acetic ether - 73.83 C
Alcohol - 78.39 C
Benzole - 80.44 C
Water - 100.00 C
Acetic acid - 117.28 C
Sulphuric acid - 337.77 C
Mercury - 350.00 C