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THE DETERMINATION OF NORMAL BOILING POINTS AT HIGH ALTITUDES LUIS W. LEVY m d OSWALDO E. PROANO Escuela Polit6cnica Nacional. Quito. Ecuador
ITIS well known that the boiling point of a substance is a function of the pressure a t which it is determined. Uncorrected boiling points obtained in laboratories located a t high altitude, where the atmospheric pressure is lower, are no longer useful for the characterization of a substance. For example, the boiling temperature of a substance as determined in Quito, located a t 9360 feet above sea level where the atmospheric pressure is about 547 mm. Hg, may he 10°C. lower than its normal boiling point. Corrections can be obtained by calculation or by the use of nomographs for this purpose such as that proposed by Myers.' We have found that a pressurized distillation apparatus is useful for the direct determination of the normal boiling point, regardless of the outside atmospheric pressure. Pressurized systems have been used earlier for studies of the coefficient of heat transfer and boiling rate of l i q ~ i d s . ~The apparatus employed by us is similar to that commonly used for distillation at reduced pressure, with the vacuum pump replaced by a blower pump. The latter is put into operation until 'MYERS,R.,J. CHEM. EDUC., 34. 58 (1957). 'CICHELLI,M. T.,AND C. F. BONILLA, T~ans.Am. In&. C h a . Eng~s.,41, 755 (1945).
the mercury manometer shows an inside pressure of about 770 mm. Hg. The stopcock A is closed, the pump disconnected, and the stopcock opened slightly until the pressure falls to 760 mm. Hg. Heating of the distillation flask is started. Just before boiling begins the pressure is readjusted to exactly 760 mm., and the boiling point is determined in the usual way. If the system is reasonably sealed, no variation in pressure will occur for the short time necessary for the determination. However, t o minimize any changes of pressure within the system, an empty flask representing two or three times the apparatus volume may be connected between the manometer and the distillation assembly. The apparatus should be useful for the determination of normal boiling points in any laboratory located at an altitude above 3000 feet.
JOURNAL OF CHEMICAL EDUCATION
