Thomsen calorimeter

Na2S04 (c, II). The data on the heat of solution yield the following values for S4m- Thomsen,18 0.257 Tilden,2 0.25 Pickering,8 —0.09. Other data on the heat of solution, lacking in most cases necessary information as to temperatures and concentration, were reported by Graham,1 Favre and Valson,2 Berthelot,10 Berthelot and Ilosvay,1 and Varali-Thevenet.1 Mixter6 measured, in a bomb calorimeter, the heat... 

In a method used by Thomsen the given liquid, e.g. a solution, was used as the calorimeter liquid and heat given to it by the combustion of hydrogen or by a chemical reaction (e.g. the dilution of sulphuric acid, in a vessel immersed in the liquid. A known mass of heated solid can also be immersed in the liquid in a calorimeter. Schiff enclosed the liquid in a platinum vessel of cross-shaped section, containing a thermometer. This was heated to a given temperature and then put into the calorimeter, and stirred round in the water. The liquid was in layers only 1 cm. thick and a rapid equalisation of temperature was thus ensured. Schlesinger heated the liquid electrically and deduced the rise in temperature from the measured increase in volume and the coefficient of expansion. Specific heats of liquids at low temperatures ca,n be determined by a modification of the Nernst calorimeter, in which the liquid in a small steel vessel contained in a... 

Any of the calorimeters described in Chapter II. is in principle capable of being used for the determination of heats of reaction. In any actual case it will, of course, be necessary to adapt the apparatus to the purpose which it is intended to serve. Jul. Thomsen, Berthelot, Favre and Silbermann, Stoh-mann, de Forcrand, Luginin, and of late years Th. W. Richards, AVrede, and W. A. Roth have been the chief workers in the development of thermo-chemistry. The more important of the apparatus devised and used by them are described in detail in many text-books. 

It is necessary to distinguish between the total heat of solution and two other kinds of heat of solution. The first of these is the heat evolved when 1 mol of the solute is dissolved in a very large volume of solvent so as to form a very dilute solution. This is generally spoken of simply as the heat of solution. It is the easiest to determine experimentally, as solution proceeds so rapidly in the presence of a large amount of solvent, that the heat evolved can be measured in a calorimeter. Thus most of the published data, such, for example, as the numerous determinations of J. Thomsen, are given in terms of this heat of solution. It differs from the integral heat of solution by the heat evolved when the saturated solution is diluted indefinitely.. ... 

The E.M.F. was practically always measured at atmospheric pressure for Wp, the heat evolution at constant pressure, were introduced the data, e.g. of Thomsen, which also relate to the heat developed in a calorimeter when the reaction takes place under atmospheric pressure. I have been unable to find an explanation of this either by Helmholtz, Czapski, or their immediate followers probably it was tacitly assumed (as it happens, rightly) that, in galvanic... 

Figure 4. Two historical calorimeters of the passive adiabatic group the Thomsen (left) and Berthelot (right) calorimeters...

Ordinary, with a central vessel and double-walled surroundings. Typical calorimeters mentioned in this group are the Thomsen mixing calorimeter and the Dewar vessel calorimeter. 

Using such a calorimeter (from the Latin for heat-measure), Berthelot ran careful determinations of the quantity of heat evolved by hundreds of different chemical reactions. Independently, the Danish chemist Hans Peter Jorgen Julius Thomsen (1826-1909) did similar experiments. 

Harsted and Thomsen determined a calibration constant for their LKB calorimeter by using various results determined by Marsh and co-workers. They estimated that their modified flow calorimeter was accurate to about 2 J mol. Goodwin and Newsham have described a flow calorimeter for use with alcohol + water systems. 

Further thermochemical measurements were made in the 1850s and 1860s by the Danish chemist Julius Thomsen (1826-1909) and the Frenchman Marcelin Berthelot, who had earlier made such important contributions to organic synthesis (Chapter 10). It was Berthelot who introduced the terms endothermic and exothermic and invented the bomb calorimeter for the accurate determination of heats of combustion. Berthelot suggested that all spontaneous reactions occur with the evolution of heat, and that the reaction which actually occurs in a given situation is the one which is accompanied by the greatest evolution of heat. These conclusions are erroneous, and it was not until the new discipline of thermodynamics was more fully developed that the criteria for spontaneous chemical change were properly understood. 

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