Thermocouples constancy

A vacuum flow apparatus was used in experiments on hydroxyl reactions (Fig, I). The free hydroxyl, together with other active species and nondisssociated water molecules, was pumped out of the high-voltage discharge zone into the reaction vessel, through a nozzle. The substance studied was introduced into the reaction vessel from a flask of prefixed volume, through a stopcock valve. The reaction vessel was heated by means of an electric furnace. The temperature constancy was checked by means of thermocouples at various sites in the reaction vessel. 

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 The column is allowed to achieve equilibrium before any material is withdrawn.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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