mercury contact for constant temperature thermoregulator

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MERCURY CONTACT FOR CONSTANT TEMPERATURE THERMOREGULATOR' MICHAEL CEf OLA and ARTHUR J. CHADWICK Fordham University, New York City, New York

rigurs 1

A DEVICE for the precise regulation of temperature in constant temperature baths has been constructed and used with very good results in our laboratory. This Based in part on work performed under contract for the Atomic Energy Commission, Ken, York Office.

instrument, after calibration, eliminates the "hit or miss" control that is necessary with ordinary regulators. The essential constructional features of the mercury contact herein described are illustrated in Figures 1 and 2. Regulation of the temperature is brought about by the rotation of the calibrated drum B (Figure 1) about the stationary member C. This causes the threaded spindle D to move up or down, as a result of which the needle-like steel wire at the end of the spindle will make or break contact with the mercury thread in the capillary of a glass thermoregulator. Stainless steel is to be preferred for part D because of its great resistance to corrosion. The drum B has 50 divisions and the number of threads on screw component D are such that one small division is equivalent t o 0.001 inch. To facilitate keeping track of the distance of movement of the needle the flat portion of spindle D is marked in quarter inches, each equivalent to 250 units on the drum B. Part A is simply a "lock-nut" to prevent the movement of B once the setting has been chosen. Very specific details of the construction of the various component parts of the mercury contact are shown in Figure 2. The device may be calibrated with the aid of a Beckman thermomet.er immersed in the bath and

A U I U N U Y PARTS UNLESS STATED OTYERWISE.

STANDARD NCTRICU TCRYIWAL.

MARCH, 1954

indicating the temperature ohtained with each setting of the calibrated drum. Enongh time is allowed after each adjustment of the setting to insure the attainment of constant temperature. The precision of the instrument was tested-by starting at the lowest setting of the drum and then making frequent changes until the maximum temperature range was reached. This was followed by a repetition of the drum settings in such a way that the temperature was brought down on exactly the same course as it was taken up. The data obtained for the particular glass thermoregulator in use in our laboratory are shown in the table. The temperatures recorded are in degrees centigrade and the drum settings in inches. By plotting average temperature values versus drum settings a calibration curve may be constructed, as shown in Figure 3, from which any desired temperature Temperatures in ' C . at Various D r u m Settings

E m . no.

1.250

Drum settin-1.000 0.750

0.500

0.250 Drum eetting in inches Figtlre 3

-40. temp.

25.668

Au. deviation &0.022

26.846

28.027

1 0 . 0 1 6 +0.012

29.210

30.396

+O.W9

10.002

may he ohtained for the bath by the appropriate choice of drum settings. With our instrument the precision of such calibration was better than 0.02°C. The range

of working temperatcres will of course depend upon the particular combination of capillary tubing in the thermoregulator andupon screw length. An immediate improvement in the apparatus consists in the tapering of the lower member of part C in Figure 1 so that it may fit a standard taper female joint attached to the upper end of the glass thermoregulator