11.150 |
SECTION 11 |
11.11 CORRECTION FOR EMERGENT STEM OF THERMOMETERS
When a thermometer which has been standardized for total immersion is used with a part of the liquid column at a temperature below that of the bulb, the reading is low and a correction must be applied. The stem correction, in degrees Celsius, is given by
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KL (to |
tm ) degrees Celsius |
where K |
constant, characteristic of the particular kind of glass and temperature (see Table 11.49) |
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L |
length of exposed thermometer, |
C (that is, the length not in contact with vapor or liquid |
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being measured) |
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to |
observed temperature on thermometer |
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tm |
mean temperature of exposed column (obtained by placing an auxiliary thermometer |
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alongside with its bulb midpoint) |
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For thermometers containing organic liquids, it is |
sufficient to use |
the approximate value, |
K |
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0.001. |
In such thermometers the value of |
K is practically independent of the kind of glass. |
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TABLE 11.64 Values of |
K |
for Stem Correction of Thermometers |
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Temperature, |
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C |
Soft glass |
Heat-resistant glass |
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0– 150 |
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0.000 |
158 |
0.000 |
165 |
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200 |
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0.000 |
159 |
0.000 |
167 |
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250 |
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0.000 |
161 |
0.000 |
170 |
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300 |
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0.000 |
164 |
0.000 |
174 |
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350 |
0.000 |
178 |
400 |
0.000 |
183 |
450 |
0.000 |
188 |
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