Nemst-calorimeter

The Nemst calorimeter is a calorimeter for the measurement of specific heat capacities at low temperatures. The sample to be measured is suspended in a glass or metal envelope that car be evacuated. The sample is heated by means of a platinum wire located in a bore inside the sample. The wire also serves as a resistance thermometer. The specific heat capacity is determined by recording the temperainre rise in the sample for a given delivery of energy. 

The Nemst calorimeter is used for low-temperature heat capacity measurements. The sample is contained in a small metal case equipped with a heater and thermometer and is placed in an isoperibol (isothermal) jacket of large heat capacity, which in turn is surrounded by an evacuated chamber surrounded by, for example, a liquid N2 or H2 chamber (Fig. 11.77). A variant is to use an adiabatic jacket. Of course, what is measured is not Cp, but a hopefully reasonable approximation to it ... 

Further developments in calorimetry include the invention of the twin- calorimeter" by Joule (1845) and its modification by Pfaundler (1869XRef 25,p 543) "phase- change calorimer (isothermal) of Bunsen(Ref 15,p 796 Ref 25,p 547) "labirinth flow calorimeter (Ref 25,p 549) "adiabatic calorimeter (nonisothermal), first used by Richards in 1905 (Ref 15,p 797) and modified by Yost, Osborne others (Ref 25,p 550)(See also Ref 3,p ll6)(Parr adiabatic calorimeter is described in Refs 16 29) "constant- temperature- enviroment calorimeter", first used by Nemst in 1907, was modified by Giauque in 1923(Ref 15>p 797)... 

The Copper Calorimeter.—The first description of this apparatus was given by W. Nemst, F. Koref, and F. A. Lin-demann (36) detailed instructions for its use were given later by Koref (60), who has carried out a large number of valuable measurements with it. The work was then continued by A. S. Russell (79a) and Ewald (99) the latter, in the examination of ammonium compounds, discovered the remarkable fact that there is here a transient decrease of specific heat with rise of temperature over a certain range, which points to internal rearrangements in the ammonium radicle. 

The heat capacities were measured using a Nemst vacuum calorimeter. Analysis of the zirconium indicated the following impurities 0.025% Hf, 0.67% Fe, 0.15% C, 0.026% N and 0.082% other impurities. The data were corrected for the iron impurity in the zirconium but represented a maximum correction of 0.3% in the heat capacities. The samples could not be analysed for oxygen but, on the basis that the content of N was low, the author surmised that the oxygen content would also be low. Fifty measurements were taken from 14.4 to 298.2 K. The heat capacities obtained from the meas-... 

Adiabatic calorimeters have only become possible with advanced designs for electrical temperature measurement and the availability of regulated electrical heating. The first adiabatic calorimeter of this type was described by Nemst in 1911 [9]. Special equipment is needed for low-temperature calorimetry, below about 10 K as are described in Sect. 4.3. Modem calorimeters [10-13] are more automated than the adiabatic calorimeter shown in Fig. 4.33, but the principle has not changed from the original design by Nemst. 

Measurements of specific heats are generally performed in adiabatic calorimeters. For investigations into the solid state behavior of polymers the nonisothermal adiabatic calorimeter as first described by Nemst (1) is most useful. Basically such a calorimeter consists of an inner sample compartment, an outer heat insulating jacket, a heater and a thermometer. The specific heat of a material is by definition ... 

At the suggestion of Nemst, Eucken (1909) developed a calorimeter for the measurement of specific heat capacities at low temperatures. Nemst (1910, 1911) used a similar calorimeter without major modifications for the measurement of a large number of specific heat capacities to a temperature of 23 K. To test his own heat theorem ( third law of thermodynamics), Nernst strove to measure the specific heat capacity as much point by point as possible as a function of temperature. An average specific heat capacity over a relatively large temperature range was worthless for this purpose. 

Figure 7.29 Calorimeter of Eucken and Nemst for the determination of specific heat capacities (from Eucken, 1909).

The isoperibol calorimeter is also termed an enviromnent constant-temperature calorimeter. The famous Nemst-type calorimeter is a typical low-temperature isoperibol calorimeter. Before the 1940s, the enthalpies of phase transition and heat capacity of hundreds of organic compounds were determined with an inaccuracy of between +0.5 to 0.2 percent by Nemst-type calorimeters. Low temperature adiabatic calorimeters were developed based on the Nemst-type calorimeter, and, at present, adiabatic calorimeters have replaced Nemst-type for most low temperature heat capacity and phase change measurements on organic compounds. Besides the Nemst-type calorimeters, the term isoperibol calorimeter also refers to other types of environment constant-temperature calorimeters such as the commercial LKB-microcalorimeter. 

In a measurement of heat capacity, one determines the heat required to increase the temperature of the sample 1 K [see Eqs. (4) and (11) of Fig. 1.2]. It was alreacty discussed in Fig. 5.4 how to measure heat capacity in steps using a Nemst-type calorimeter. 

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