Picker calorimeter

Hahn et al. (1990) measured the excess enthalpy of binary liquid systems with a commercial Picker calorimeter (Setaram, France unfortunately, this is not available anymore) with a precision of about 2%. 

The only difficulty with using this method is the lack of heat capacity data. With the wide spread use of the Picker et al. (129) heat capacity calorimeter one can usually find published heat capacities for most systems of interest (3) at 25°C. Since the Cp does not attribute much to the adiabatic correction, this is not a serious limitation. 

Standard heat capacities of transfer can be derived from the temperature dependence of standard enthalpies of solution (8). While this technique can give general trends in the transfer functions from water to mixed solvents (9), it is not always sufficiently precise to detect the differences between similar cosolvents, and the technique is rather laborious. Direct measurements of the difference between heat capacities per unit volume of a solution and of the solvent a — gq can be obtained with a flow microcalorimeter (10) to 7 X 10 5 JK 1 cm-3 on samples of the order of 10 cm3. A commercial version of this instrument (Picker dynamic flow calorimeter, Techneurop Inc.) has a sensitivity improved by a factor oi about two. 

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... 

A third way of measuring the heat exchanged in a passive diathermal calorimeter is to make use, in the surrounding thermostat, of a peripheral liquid flow (usually water) whose temperature change is determined. This is the principle followed by Junkers flame calorimeter [39], the Picker liquid mixing calorimeter [40], and modem reaction calorimeters developed for safety studies of chemical reactions. 

Infrared spectra were recorded on a Nicolet 20 DX FTIR spectrometer, and glass transition temperatures were obtained on a Perkin Elmer DSC-4 differential scanning calorimeter. Radiographic measurements were carried out with a Picker X-ray unit operating at 90 kV and 6 mA using cylindrical polymer specimens of known thickness. Radiopacities were compared with that of an aluminum stepwedge with 1 mm steps. Experimental details have been published elsewhere [9]. 

There are open nonisothermal-nonadiabatic calorimeters like those of Picker, Jolicoeur and Desnoyers [191-193]. 

Figure 27. Schematic diagram of a flow calorimeter after P. Picker (Selaram)...

This calorimeter (Picker, Jolicoeur, and Desnoyers, 1969) represents a twin instrument with countercurrent auxiliary circulation (Figure 7.24). All liquids are brought to a constant temperature at the inlet. The reactants are mixed with one another before entering the first flow tube, and the heat of reaction is transferred in a heat exchanger from the reaction product to the auxiliary liquid, which flows in the opposite direction. In the second flow tube - also connected by means of a second heat exchanger with a counterflowing auxiliary liquid - a nonreacting reference liquid (e.g., the reaction product) flows. The temperature difference between the two countercurrents is measured it is proportional to the heat flow rate of the reaction. The calorimeter is equipped with electric calibration heaters. 

A special version of this twin-type flow calorimeter (Picker et al., 1971) serves for the measurement of the specific heat capacity of liquids. Both flowing liquids -sample and reference - are heated separately with an electric basic power P . This results in a temperature difference owing to the difference between the specific heat capacities of the two liquids. This temperature difference is eliminated by the... 

Figure 7.24 Flow calorimeter designed by Picker, Jolicoeur and Desnoyers (according to Picker, Jolicoeur, Desnoyers, 1969).

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