30 
BULLETIN 1036, U. S. DEPARTMENT OF AGRICULTURE. 
may be as great as 10° C. at the temperature used in distilling creosote 
oil. The formula for making the correction for this error is given in 
various ways. That adopted by the United States Bureau of Stand- 
ards is F (T-t) N, in which T equals the observed reading of the 
thermometer; t, the average temperature of the emergent stem, 
obtained by placing another thermometer with its bulb at the center 
of the emergent stem; N, the number of degrees emergent, and F 
a factor for the termometer depending upon the difference of expansion 
of glass and mercury. This factor varies from about 0.00015 to 
0.00017; for Jena borosilicon glass the factor is 0.000158. Some 
idea of the size of these corrections may be obtained from Table 11. 
Table 11. — Corrections for emergent stem. 
T. 
t. 
N. 
Correc- 
tion. 
T. 
t. 
N. 
Correc- 
tion. 
200 
210 
270 
280 
52.0 
53.5 
70 
80 
2.4 
2.9 
42 
10 
3 
220 
43.5 
20 
.6 
290 
55. 
90 
3.4 
230 
45.0 
30 
.9 
300 
57.0 
100 
3.9 
240 
47.0 
40 
1.2 
310 
58.5 
110 
4.4 
250 
48.5 
50 
1.6 
320 
60.0 
120 
5.0 
260 
50.0 
60 
10 | 
360 
70.0 
160 
7.5 
It is obviously impossible to perform the calculations necessary 
for this correction and at the same time watch a distillation in which 
fractions are being taken every 10 degrees. In this work, therefore, 
the position of each thermometer was fixed in respect to the distilling 
vessel and a table was worked out with different values for t. One of 
these tables is shown below (Table 12). It also makes correction for 
the errors in the thermometer caused by the irregularities in its 
construction. 
Table 12. — Emergent-stem corrections used with thermometer Xo. 1 , 
Temp- 
erature 
desired 
when 
cor- 
rected. 
Temperature to be read when— 
Temp- 
erature 
desired 
when 
cor- 
rected. 
Temperature to be read when— 
<=60. 
t=70. 
t=m. 
t=90. 
<=60. 
t=70. 
/=80. 
<=90. 
°C. 
180 
205 
215 
225 
235 
245 
255 
°C. 
180.9 
205.9 
°C. 
°c. 
°C. 
°C. 
265 
275 
285 
295 
305 
315 
330 
°C. 
263.1 
272. 5 
281. S 
291.2 
300.6 
310.2 
324.4 
°C. 
263. 2 
272.5 
281.9 
291.4 
300.7 
310.3 
324. 6 
°C. 
°C. 
215.7 
225.2 
234.8 
244.2 
253. 7 
282.0 
291.5 
300.9 
310. 5 
324.7 
301.0 
310.6 
324. 9 
:::::::::::::::: 
t 
With this table before the operator, it was necessary only to de- 
termine t by a small thermometer hung in the air beside the standard 
and, by reference to the table, determine the exact point at which 
the cut should be made. The differences in these corrected readings 
