Cottrell pump

Fig. 1-11. Modified Cottrell pump. (Courtesy of Dr. A. Choppin and Journal of Chemical Education.)...

Occasionally, the true boiling point of a liquid is needed, and in this case, a modified Cottrell pump is usually used (Fig. 1-11). The pump forces a mixture of the liquid and its vapor over the thermometer, which then reads the true boiling point. 

Apparatus equipped with a Cottrell pump has also proved suitable for systems with relatively high volatilities AKp. > 100°C) [H5]. The improved Labodest circulating apparatus makes use of a Cottrell pump and electromagnetic valves with Teflon cones for sample withdrawal [112]. Its microscale construction is designed along the same lines and requires only 100 ml charge (Fig. 50). The sources of error... 

Labodest circulation-type apparatus with Cottrell pump... 

Figure 2 Recirculating still. C, boiling flask, D, Cottrell pump, R, thermometer well and droplet separator , H, I, condensers , F, G, receivers with electromagnetic valves (Reproduced by permission from Austral. J. Sci. Research, 1952, 5A, 530)...

The most serious problem in all ebulliometry is the superheating of the solution before it starts boiling. This is avoided in the setup of Fig. 3.13 by the use of the Cottrell pump. This pump works on the same principle as a standard coffee percolator. The vapor developed at the bottom of the flask, at the position of the heater, carries an interrupted stream of liquid up onto the thermocouples that measure the solution temperature. On its way up, the vapor can reequilibrate constantly with the solution. The equipment shown schematically in Fig. 3.13 is capable of a precision of 0.015 millikelvin. If one uses the constant for benzene and a concentration of 0.1%, it can be estimated that this apparatus should be capable of measuring molecular masses up to 100,000. Indeed, molecular masses of this magnitude have been determined with this equipment. Unfortunately, no commercial instruments that can reach such high precision seems to be available. 

This paper describes an ebulliometric system for routine and special determinations of molecular weights. The system uses a simple ebulliometer, an immersion heater, and a Cottrell-type pump. Temperature sensing is by differential thermopile. Precision varies from about 1 to 6%, and values compare well with those from other laboratories and those from other methods. Values as high as 170,000 have been successfully measured. Some problems encountered in using the ebulliometric method are selection and effect of reference temperature, limitations of the vapor lift pump and a possible substitute for it, measurement of equilibrium concentrations within the operating ebulliometer, and the experimentally determined ebulliometric constant and some factors which influence its value. 

Tn the Cottrell method, the thermometer is placed in the vapor phase above the surface of die liquid and the apparatus so designed that boiling liquid is pumped continuously over the bulb of the thermometer. 

These free electrons give sodium and the other metals their high electrical conductivity. Pump in an electron at one end of a metal wire, and another electron from an almost identical orbital pops out at the other end. The delocalized electrons of the metallic bond ensure that little energy is required for this process, making metals highly conductive and the preferred material for power lines. It also led the renowned materials scientist Sir Alan Cottrell to propose a new definition of a metal Metals, he wrote in a 1960 article, contain free electrons. ... 

Pump seals and demister wash receive priority on fresh water additions. In the Research-Cottrell process, two demisting stages insure adequate mist removal. Water sprays are mounted below and above the... 

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