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LABORATORYTHERMOREGULATOR JOHANNES S. BUCK The Burroughs Wellcome and Company, U. S. A,, Experimental Research Laboratories, Tuckahoe, N. Y.
A VERY simple thermoregulator, suitable for maintaining a medium-sized thermostat a t a moderate temperature above the surroundings, may be constructed by applying the idea of shorting out the heating element by the expansion of the thermoregulator fluid. This avoids the diaculties encountered when contact is made by the contraction of the fluid. The apparatus is used directly on a 110-v. A.C. line, without resistances or relays. The glass part is readily constructed from pyrex glass tubing, 8 mm. o.D., and pyrex capillary, 8 mm. O.D. and 0.8 mm. I.D. The bulb is made from pyrex tube 25 mm. O.D. or larger. Mercury is used as the fluid, but toluene may be used in an inverted bulb. The external lamp serves as resistance. The heater in the bath may also be a lamp. The sizes of the lamps may be varied according to requirements. In a specific case, a 60-w. lamp in the bath, and a 100-w. lamp outside, kept 40 liters of water, in an uninsulated thin glass tank, a t 25°C. Of course, some form of stirring - device must be used in the tank. The setting of the regulator is effected by adding mercury through the side-arm and by moving the contact wires. The latter are then fixed by melting a little sealing wax into the tops of the capillaries. Adjustment is not lost by allowing the bath to become cold. Resetting, if necessary, is accomplished by adjusting the contact wires, the sealing wax being softened by gentle flaming. No trouble is experienced through arcing if the contact wire (Cbromel, 18 S.W.G.)
be carefullv filed to a blunt point and centered by @ing it a slight spiral kink CIRCUIT
lent
T o Regulator
Natrr .-..-. L~"tl
1 Toluene
