is carried out the delay setting on the second clock must be considerably increased to allow for the increased heat transfer time.
The initial trials will indicate at what value the cold bath temperature must be maintained in order to supply the required vapour generator temperature.
If this initial information is not available then the use of the thermocouple in the vapour generator together with a longer delay setting should, after an initial period of uncertainty during which the vapour may not be used, prove to be quite satisfactory.
It is probable that the temperature recorded by a thermocouple imbedded deeply into the material in the vapour generator will record a different temperature from that recorded by a thermocouple imbedded into the material near the surface from which the vapour is being removed. In this case the temperature of the thermocouple near the surface is the temperature at which control is necessary and the thermocouple must be continually lowered into the vapour generator as the surface recedes.
Frequent adjustment of the thermocouple level may be abrogated somewhat by the use of a vapour generator designed to provide a large surface area of source material.
The controller is shown in Figure 2. D. G. Burgess is now with the Universal Grinding Wheel Co. l.td.