Low-temperature bath

Carbon dioxide is used in the manufacture of sodium carbonate by the ammonia-soda process, urea, salicyclic acid (for aspirin), fire extinguishers and aerated water. Lesser amounts are used to transfer heat generated by an atomic reactor to water and so produce steam and electric power, whilst solid carbon dioxide is used as a refrigerant, a mixture of solid carbon dioxide and alcohol providing a good low-temperature bath (195 K) in which reactions can be carried out in the laboratory. 

A cold finger condenser packeFriedrichs condenser in combination with a circulating low-temperature bath (— 70°) is more convenient. 

When a flask containing orange NO2 gas at room temperature (top) is cooled in a low-temperature bath... 

B. Slush Baths. Liquid nitrogen and Dry Ice are convenient and inexpensive refrigerants. But, as shown in the examples in this chapter, a wider range of low-temperature baths is necessary for trap-to-trap fractionation of gases and for the characterization of a substance by vapor pressure measurements. A convenient constant-temperature slush bath consists of a mixture of a frozen compound in equilibrium with its liquid. The bath is made in a clean Dewar no more than... 

E. Separations. The basic filtration operation has been previously illustrated. Low-temperature filtrations for the collection of thermally sensitive compounds or products which arc soluble al higher temperatures may be performed with an H-type Schlenk tube. Fig. 1.30, in a large low-temperature bath. The jacketed, fritted funnel illustrated in Fig. 1.25 also permits low-temperature filtration. 

A more common method for preparing a low temperature bath is to mix an organic substance with either dry ice or liquid nitrogen. Dry ice (C02, —78 °C) can be added in small lumps to the solvent until a slight excess of dry ice remains. Alternately, liquid nitrogen (N2, —196 °C) can be poured into the solvent until a slush is formed that consists of the solid-liquid mixture at its melting point. 

The method has also been applied by us 52). A sample of 20 g. of catalyst 5421 is brought into the reactor (volume about 300 cm.3) and reduced and evacuated in the usual way. The vessel is then immersed in a low-temperature bath, and a hydrogen isotope is adsorbed on the surface. The vessel is evacuated to a few mm. Hg and another hydrogen isotope introduced to a pressure of 60 cm. Hg. This gas is circulated by means of a magnetic pump, as a consequence of which the catalyst may exchange... 

A thermometer is based on a reversible heat engine, which operates between a boiling water bath and a heat reservoir at a lower temperature. The boiling water bath is defined to be at 373°. The temperature of the low temperature bath is determined from the efficiency with which the engine converts heat withdrawn from the boiling water bath to mechanical energy. Derive an explicit equation, Tc = /(e), from which the temperature of the low-temperature bath can be calculated. 

The analysis of the products called for supplementary data on the decreases in vapor pressure produced by low temperature baths. After removal of hydrobromic acid, ethylene and unsaturated compounds the residual gas was subjected in different cooling baths to the temperatures listed in Table V and the cor-... 

The pyrolysis products were separated by trapping in various low temperature baths and the residual noncondensable gases were pumped into a known volume, where the pressure was measured and samples were taken for mass spectro-metric analysis. Samples of the liquid products could be taken for analysis by both mass spectrometry and gas liquid chromatography (GLC). Samples of materials for identification of products were obtained as follows ... 

This method uses a turret with multiple ports (a manifold) to which flasks and vials are fitted via suitable valves (see Fig. 2.3). The product is either frozen in a freezer (by direct submersion in a low-temperature bath) or shelf-frozen, depending on the nature of the initial and end product, and also on the volume to be freeze-dried. The pre-frozen product must be immediately attached to the drying chamber or manifold to prevent... 

A thermodynamic engine operates cyclically and reversibly between two temperature reservoirs, absorbing heat from the high-temperature bath at 450 K and discharging heat to the low-temperature bath at 300 K. 

Note that if the Carnot heat engine is operated as shown in Fig. 4.3-2 it absorbs heat from the high-temperamre bath, exhausts heat to the low-temperature bath, and produces work. However, if the engine is operated in reverse, it accepts work, absorbs heat from the low-temperature bath, and exhausts heat to the high-temperature bath. In this mode it is operating as a refrigerator, air conditioner, or heat pump. 

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