30 



BULLETIX 1036, U. S. DEPAETMEXT OF AGEICULTrRE. 



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 borosihcon 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. 



V. 



Correc- 

 tion. 



T. 



t. 



V. 



Correc- 

 tion. 



200 

 210 







i 



270 

 2.S0 



.52.0 

 53.5 



70 

 SO 



2.4 

 2.9 



42 



10 



6.3 1 



220 



43.5 



20 



.6 



290 



5.5.0 



90 



3.4 



230 



45.0 



30 



.9 1 



300 



57.t) 



100 



3.9 



240 



47.0 



40 



1.2 



310 



5S.5 



110 



4.4 



250 



48.5 



50 



1.6 



320 



60.0 



120 



5.0 



260 



50.0 



60 



2.0 



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 No. 1. 



Temn- 

 erature 

 desired 

 when 

 cor- 

 rected. 



Temperature to be read when— 



Temp- 

 erature 

 desired 

 wheu 

 cor- 

 rected. 



Temperatiuc to be read v 



hen— 



<=60. 



<=70. 



t=sn. t=90. 



t=m. 



<=70. 



<=80. 



t=m. 



"C. 



180 

 205 

 215 

 225 

 235 

 245 

 2.55 



180.9 

 205.9 



°C. 



"C. »c. ' 



"C. 



265 

 275 

 28,5 

 295 

 305 

 315 

 330 



°C. 

 263. 1 

 272. 5 

 281. S 

 291.2 

 300.6 

 310. 2 

 324.4 



263. 2 

 272. 5 



"C. 



"C. 









215. 7 

 225.2 

 234.8 

 244.2 

 253. 7 





281. 9 

 291.4 

 300.7 

 310.3 

 324. 6 



282.0 

 291.5 

 300.9 

 310.5 

 324.7 













301.0 

 310.6 

 324.9 









1 











With this table before the operator, it was necessary only to de- 

 termine i 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 



