NOTE 21—Groups 1 and 2, once the final heat adjustment is made, the
vapor temperature/thermometer reading will continue to increase. As the
distillation nears the end point (final boiling point) the distillation typically
achieves dry point first. After the dry point has been achieved the vapor
temperature/thermometer reading should continue to increase. The bottom
of the flask will be dry but the sides and neck of the flask and the
temperature sensor will still have vapor condensate present. The vapor
condensate may have the appearance of a white cloud of fumes. This
vapor condensate/cloud of fumes should totally engulf the temperaturemeasuring
sensor before the vapor temperature starts to decrease. If these
observations do not occur, the end point may not have been reached. It
would be advisable to repeat the test adding additional heat to the final
heat adjustment. Typically the vapor temperature will continue to rise as
the dry point is reached and the vapor cloud engulfs the temperaturemeasuring
sensor. When the end point is near, the rate of temperature
increase will slow and level off. Once the endpoint is reached the vapor
temperature will start and continue to decrease. If the vapor temperature
starts to decrease but then increases and repeats this cycle while the vapor
temperature continues to increase you have added too much heat to the
final heat adjustment. If this is the case, it would be advisable to repeat the
test lowering final heat setting.