Volumetric Expansion Thermometers

When you mention thermometers, volumetric expansion thermometers are what typically come to mind (see Fig. 2.30). The material that expands within a volumetric expansion thermometer is typically mercury or (ethyl) alcohol. Another name for a volumetric expansion thermometer is a liquid-in-glass thermometer. The parts of a standard liquid-in-glass laboratory thermometer are as follows ... 

It is assumed that this assirmption also holds when the thermometer is not entirely submerged in the medium of which the temperature should be measured. The impact of the volumetric expansion of the glass and the heat transfer throngh the glass on the operation of the... 

A hquid thermometer works on the principle that the specific mass or density is a function of the temperature. The volumetric expansion of the volume is therefore a measure for the increase in temperature. 

Figure 13-6 Apparatus for RESS A = SCF reservoir PV = high pressure volumetric pump HI, H2 = heat exchangers V, VI, V2, V3 = on-off valves S = saturation vessel EN = expansion nozzle E = expansion vessel F = flow meter G = rotameter PI = pressure indicator TI = thermometer.

Gas adsorption processes may last for seconds, hours or - sometimes -even days. Therefore one never can be sure whether mermodynamic equilibrium in a volumetric experiment has been reahzed. Hence the time which should elapse between opening the expansion valve and reading of instruments, especially thermometer and manometer has to be chosen according to experience or accompanying gravimetric measurements which - contrary to volumetry / manometry - also provide information on the kinetics or the sorption process, cp. Chap. 3. 

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