A
Nomograph for Emergent Stem Correction of Thermometers WILLARD T. SOMERVILLE, Elmhurst, Long Island, N. Y. where
I
T IS frequently necessary to apply correction factors to ther-. mometers calibrated for total immersion but used- a t partial immersion. The values given in various references are somewhat different and involve the use of a formula (1-4). A survey of domestic thermometer manufacturers indicates that, in general, the bulbs of ordinary range (0' to 360') thermometers are constructed of Corning Normal glass similar to Jena 16 111, while the stems are made of a soda-lead glass known as Corning G4D. (Corning G4C glass has been replaced by G4D.) Thermometers for higher ranges are normally constructed of a domestic borosilicate glass similar to Jena 59 111. The linear coefficient of expansion of these glasses and the apparent cubical expansion of mercury in these glasses are given in Table I.
T = correction in O C. 1.56 X 10-4 = apparent coefficient of expansion of mercury in glass I = length of exposed stem in ' C. To = observed temperature T , = average temperature of exposed stem
To use the nomograph, a line ?s drawn through To and T, across the nomograph. Using a 90" angle, such as a triangle or the corner of a sheet of paper, a line is drawn a t right angles to the above line through the proper point on scale 1. Where this line intersects the T axis determines the correction. A transparent sheet containing two lines crossing a t 90' will be helpful to frequent users of the nomograph.
CORRECTION - DEGREES
CENT1GRADE
When the correction is greater than 5 ', it is advisable to add the correction to T o and recompute a new correction. For hightemperature borosilicate thermometers the correction determined from the nomograph should be multiplied by 1.06.
The corrections to be added to the observed temperature are obtained from the nomograph, in the construction of which the following equation was used:
ACKNOWLEDGMENT
Table I. Glass Corning Normal Corning G4C Corning G 4 D Borosilicate a
20"
The assistance of T. C. Patton of the Baker Castor Oil Company in constructing the nomograph is appreciated.
Expansion
Linear Coefficient of Expansion 8.8 X 10-6 8.6 X 10-6 8.4 X 10-6 6.0 X 10-6
Calculated Apparent Cubical Expansion of Mercury in Glass" 1.55 X 10-4 1.56 X 10-4 1.67 X 10-4 1.64 X 10-4
LITERATURE CITED
Adams and Johnson, "Laboratory Experiments in Organic Chernistry", 3rd ed., p. 35, New York, Mrtrmillan Co., 1940. Berl and Kullman, Bey., 60, 815 (1927), a similar, though not identical, nomograph. Busse, "Temperature, Its Measurement and Control", p. 237, New York, Reinhold Publishing Corp., 1941. Reilly and Rae, "Physico-Chemical Methods", 3rd ed., Vol. 1, p. 370, New York, D. Van Nostrand Co., 1939.
Cubical coefficient of expansion'of mercury taken as 0.18186 x 10-3 at
c.
675
