Heat Theorem to condensed systems

Determination of Thermo-chemical Data by Application of the Heat Theorem to Condensed Systems —The fundamental equation of the Second Law, 

We see then that we may determine first U0) and then also U for all temperatures if— 

We have already (p. 115) had an example of such an application the values found by U. Fischer for the heat of formation of silver iodide by means of formulae (99) and (100) should be more reliable than that obtained by equation (1). For though the electro-motive force of the cell in question could be determined at one temperature with sufficient accuracy (about 1 per 1000), the temperature coefficient could not be obtained so precisely as to allow the determination of U also to 1 per 1000 by equation (1) for the use of formula (100), on the other hand, the specific heats need be known with only moderate accuracy, since they serve only to determine the relatively small difference A — U. The case is similar in the following example. 

Pollitzer found a difference which led him to suppose that, since the heat of formation of calomel is very reliable, Thomsen s value for the heat of formation of lead chloride (82,700) must be several thousand calories too small. Thereupon Koref and Braune (986) redetermined the value, using a very accurate calorimetric method, and found, as a matter of fact, the figure 85,570, which is higher by 2870. Pollitzer s suggestion, put forward on what were certainly very sound grounds, was therefore completely justified, and the criticisms directed against it by E. Cohen have proved to be unfounded (cf. paper 986, p. 196). 

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Investigations of Braune and Koref.—We are indebted to Braune and Koref (77, and particularly 986) for an extremely careful and painstaking test of the application of the Heat Theorem to condensed systems. The test was made on a number of galvanic cells in exactly the same manner as that already employed by U. Fischer. In all the cells U was found to have nearly the same value, whether determined from the temperature coefficient of the potential or by direct thermochemical means this provides a guarantee that the cells under observation were actually controlled by the process assumed to be supplying the current, though as a matter of fact there was hardly any doubt of this in the cases examined. 

Some Further Applications 0 the Heat Theorem to Condensed Systems.—The reaction discussed on page 113 has been examined in a paper by G. Jones and G. L. Hartmann, though not with the completeness with which U. Fischer and, later, Braune and Koref (p. 115), had done so. These authors limited themselves to a measurement of the temperature-coefficient ot the cell,... 

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