Regulated temperature still-heads

When a regulated temperature still-head is employed, it is better, for two reasons, to bend the tube into the form of a spiral in the first place, the effective length of the still-head may be thereby greatly increased without unduly adding to the height of the bath, and in the second place, as has been already pointed out, the spiral form is more efficient than the vertical. 

The first fractionation of all the available distillates from petroleum ether obtained with the combined dephlegmator and regulated temperature still-head, and collected between about 37 and 60°, gave no indication of the presence of any substance boiling in the neighbourhood of 50 , as will be seen by Table 77. 

The quantity of material was too small to allow of the separation being continued with the combined dephlegma-tor and regulated temperature still-head, but six additional fractionations were carried out with a 12 column dephlegma-tor, when the value of rose to 163 0 for the fraction... 

Lord Rayleigh s Apparatus.—Lord Rayleigh (2) describes an apparatus similar in principle to Carveth s except that the temperatures of both parts of the still-head are regulated by liquids and not by vapours. 

The still pot is then heated so that the liquid boils gently, and a steady reflux is returned from the head of the column. The jacket temperature is adjusted to correspond to the vapor temperature at the head if a thermometer is used, or it is adjusted to adiabatic operation if a differential thermocouple is employed. The boil-up rate (throughput) is adjusted to a value which is appropriate for the column being used (Table 1-12) by regulating the amount of heat supplied to the still pot. The column is allowed to achieve equilibrium before any material is withdrawn. This is usually determined by the constancy of the vapor temperature or of the refractive index of the material at the column head and usually requires from one-half to several hours. The time necessary for establishing equilibrium is usually greatest for the columns with the highest number of theoretical plates. 

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