Experimental Measurement and Theoretical Calculation of Low Vapor Pressures at Low Temperatures

摘要

A mercury manometer is described that measures low vapor pressures simply with an accuracy of several thousandths of a millimeter. It was used for low-temperature measurements on substances previously studied by Syndey Young in higher temperature ranges. Temperatures were determined by a mercury thermometer calibrated by the Physical-Technical Federal Institute and a platinum thermometer, which was matched to the temperature scale established by Kamerlingh Onnes by determination of the alpha value. The temperatures were established at 0.1 exp 0 for the mercury thermometer, 0.05 exp 0 for the platinum thermometer. Temperature baths of ether-carbon dioxide mixtures in the range from -10 to -80 exp 0 , petroleum ether cooled by liquid air to -60 to -130 exp 0 , liquid air (whose temperature was controlled by flows of hydrogen and oxygen) from -187 to 199 exp 0 , and liquid hydrogen for -252 exp 0 were used. Finally, the thermostat tested by Hennig at the Physical-Technical Federal Institute was used, which proved to be a useful and convenient way to hold a constant temperature in a considerable temperature range. The substances measured by Young, with very few exceptions, were subjected to the same purification procedures, so their boiling points differed only insignificantly. The observations showed that the values calculated with the Nernst vapor pressure equation are sometimes a bit higher, sometimes a bit lower, which was not surprising either, since the pressure constants were found to be 5 to 2000 mm and higher. A new tabulation of the constants, which includes the low pressure region, quickly shows the capabilities of the Nernst vapor pressure equation, since the experimental and theoretical data immediately exhibit good agreement. In addition to these measurements, two solid gases were investigated. (ERA citation 05:038432)