mercury before the instrument could be reset. Third, although the instrument could be set a t different'temperatures by sliding the wire (G) up or down in ( H ) the range in degrees was small. In order to avoid these difficulties the tbermoregulator was modified as shown in the accompanying figure. The first difficulty was avoided by the use of the bulb
AN IMPROVED THERMOREGULATOR
A. Toluene bulb B. Side tube C, D. Reservoir bulbs S.
E, F. Rubber tubes G , P. Fixed Pt contacts H. Capillary tube Stopcock
H. B. HUDDLE State Teachers' College, Johnson City, Tennessee
I N THE operation of a simple electric thermoregulator of the inverted U type three difficulties were experienced. First, the mercury in the capillary tube (H) had a tendency to lodge between the contact wire (G) and the wall of the tube whenever i t passed the tip of the wire. Second, a rise in temperature of a few degrees, when the thermostat was not in operation, caused the mercury to flow out of the top of the tube (H). Then, cooling to the original temperature allowed it to fall below the bottom of the capillary tube. This necessitated the troublesome addition of more
( C ) which receives the excess mercury from the lag in the instrument and allows it to return to the capillary without sticking. The bulb ( D ) was added to avoid the second difficulty by providing an additional reservoir. Any mercury adhering in the capillary connecting (C) and ( D ) can be returned to ( C ) by blowing in (F). The third difficulty was solved by the addition of the side tube (B). The instrument may be set a t any temperature within a wide range. When the thermoregulator has attained the temperature desired the stopcock (S) is opened and the mercury brought into contact with the tip of the wire (G) by sucking or blowing on the tube (F). The stopcock is then closed.
