A
SIMPLE ELECTRICAL T H E R M O S T A T BY FREDERICK A. OSBORK
T h e thermostat described here may, perhaps, be considered as a simpler and modified form of the electrically heated and controlled thermostat of Geer.' It was devised to offer a simple, quick, and yet accurate means of controlling the temperature in laboratory work in conductivity. T h e general details and the electrical connections are shown in the diagram. T h e heating of the 50-liter bath was accomplished by means of one layer of iron wire of five turns, carrying a 3-ampere current produced from eight storage cells.
A A -=Platinum points. B = Storage battery (8 cells). B' = Storage battery ( I cell). CC = Iron wire. D = Stirrer. E = Glass coil containing mercury. -...
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R = Relay.
Jour. Phys. Chem., 6, 85
(1902).
298
A Sample Electrical Tkevmostat T h e glass worm used as the regulating thermometer was
9.5 cm. in diameter and 16 cm. long. It holds IIO cm. of mercury. One U. S. storage cell No. 3 was used to operate the relay circuit and no harmful sparking has been noticed on the make and break of the circuit. T h e relay was one of 20-ohm resistance. T h e bath was brought to within one-tenth degree of the required temperature and then a very little adjustment of the screw P put the bath into automatic regulation. T h e bath has many times been made self-regulating within fifteen minutes. T h e large volume of mercury and the very large surface of the worm combine to make the regulator very sensitive, the relay very often throwing the current off and on while the Beckmann thermometer showed no change. On continuous runs of six to eight hours no change of ~ j r o oof a degree has been observed. T h e advantages of the thermostat are: I. The simplicity of construction and operation. 2. T h e ease and quickness with which the given temperature may be obtained. 3. Its constancy in automatically holding the temperature at the desired value. Physics Laboratory, University of Washington.
