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preface to fifteenth edition

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11.150 SECTION 11<br />

11.11 CORRECTION FOR EMERGENT STEM OF<br />

THERMOMETERS<br />

When a thermometer which has been standardized for <strong>to</strong>tal immersion is used with a part of the<br />

liquid column at a temperature below that of the bulb, the reading is low and a correction must be<br />

applied. The stem correction, in degrees Celsius, is given by<br />

KL(<strong>to</strong><br />

t m) degrees Celsius<br />

where K constant, characteristic of the particular kind of glass and temperature (see Table 11.49)<br />

L length of exposed thermometer, C (that is, the length not in contact with vapor or liquid<br />

being measured)<br />

t o observed temperature on thermometer<br />

t m mean temperature of exposed column (obtained by placing an auxiliary thermometer<br />

alongside with its bulb midpoint)<br />

For thermometers containing organic liquids, it is sufficient <strong>to</strong> use the approximate value, K <br />

0.001. In such thermometers the value of K is practically independent of the kind of glass.<br />

TABLE 11.64<br />

Values of K for Stem Correction of Thermometers<br />

Temperature, C Soft glass Heat-resistant glass<br />

0–150 0.000 158 0.000 165<br />

200 0.000 159 0.000 167<br />

250 0.000 161 0.000 170<br />

300 0.000 164 0.000 174<br />

350 0.000 178<br />

400 0.000 183<br />

450 0.000 188

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