MODIFIED WATERBATH THERMOSTAT THE REV. BROTHER HORMISDAS Saint-Stanislas High School, Montreal, Canada
S
EVERAL months ago, I undertook the preparation of butyric acid by the fermentation of lactic acid. To control the temperature of the water bath (35'C.) I constructed the thermostat described in THEJOUR-
FIGWE1 1. Air-expansion chamber-500-cc. bottle 2. Dry-cell circuit-breaker-capper wire No. 18 3. Two-hole rubber stopper holding the two U-shaped glass tubes--one opened, the other closed 4. ETVcell 5. ~ e f a y 6. Water-bath container 7. 5-mm. glass tubing, mercury-filled connectors 8. Insulating material-electrician's tape 9. Constantin heating unit
969-70 (May, 1931)l. It did not operate satisfactorily. The dry cell soon gave way, as i t was on closed circuit the greater part of the time. To overcome this difficulty I modified the apparatus as shown in Figure 1. The advantage of this arrangement is that the relay draws current from the ctll only when the main current goes through the heating unit. This advantage is offset as the difference in temperature between the water bath and the surrounding medium increases.
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However, over long periods of operation this mechanism is subject to failure. I simplified it as shown in Figure 2. The figure is self-explanatory. The device has been in continuous service during five weeks and has kept the water bath a t an almost constant tem-
1. Circuit-breaker-mercury-filled test-tube
2. Iron stand and clamp 3. 4.
Water-bath container 7-mm. glass tubing enclosing th%float 5. Float-3-mm. glass tubing .sealed to an elongated glass bulb or to a larger tubing closed a t the lower end 6 . Air-expansion bottle. 500-cc., mercury trap 7. Copper wire No. 18 sealed t o the float
perature, the slight variation dependiGg on the fluctuations of atmospheric pressure. The sparking in the mercury circuit breaker (1) is quickly minimized due to the formation of a copper amalgam which clings to the copper wire, and of a cuplike depression on the mercury level.
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