Details of Calorimeter Construction

Given the availability of modem instrumentation, the contemporary chemist is spared the meticulous and laborious procedures followed in early hydrogen thermochemistry (see, for example, Kistiakowsky, et al., 1935, 1936). Only two more recent hydrogen calorimeter implementations are recommended to the scientist who wishes to pursue this line of research, one a commercial instrument (Tronac Inc. Orem, UT, USA) and one that can be constructed from standard laboratory equipment with a few modifications. 

Because the commercial instrument used by Roth has been fully documented (Christensen et al., 1973), the home made device will be more completely described here. We have constructed calorimeters from a design that has evolved with use over a number of years (Rogers, et al., 

Miniaturization is especially advantageous in an era when compounds with extraordinarily interesting structural and thermochemical properties are being synthesized but only in very small amounts. Because the first principle of all calorimetry is that the sample must be well defined and pure (or at least have a small amount of known impurity), microcalorimetry permits use of a wider range of contemporary purification techniques, especially preparative gas chromatography, than traditional calorimetry. There is, of course, no reason to suppose that the evolutionary process of hydrogen calorimeter design cannot be continued to produce smaller, safer, and possibly more accurate instruments. 

The calorimeter used in our laboratory was a 25 ml Erlenmeyer flask sealed by means of a serum stopper (Z 10,076-5, Aldrich Chem. Co., P. O. Box 2060, Milwaukee, Wisconsin 53201, USA) containing about 10 ml of a stirred slurry of catalyst and a noninteracting, nonpolar solvent, typically n-hexane, but possibly one of many other choices, as the occasion demanded. 

The temperature monitoring circuit consisted of a thermistor (YSI.com) protruding through the serum stopper into the slurry and connected as one arm of a conventional Wheatstone bridge powered by 

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