METHODS OF ANALYSIS USED. 



15 



Comparison of differences of temperature and of volumes distilled, due to emergent stem 



of thermometer . 



[200 cc of turpentine distilled.] 



1 Thermometer immersed in vapor only. 



The table shows that No. 1 turpentine begins to distill at 157 C. 

 (315 F.) by the immersed thermometer and at 153.5 C. (308 F.) by 

 the emergent thermometer. At 160 C. (320 F.) by the immersed, 

 108 cc had distilled, and by the emergent thermometer 166 cc. At 

 165 C. (329 F.) by the immersed thermometer 173 cc had dis- 

 tilled, while about 180 cc had passed over when this temperature was 

 reached by the emergent thermometer. It will be noted also that as 

 the temperature rises, the difference between the readings of the two 

 thermometers first decreases and then increases; the difference in 

 reading being least where approximately the largest volume of dis- 

 tillate is yielded. These facts are brought out still more strikingly 

 in the distillation of turpentine No. 2. The lag of the emergent stem 

 thermometer is also shown in the comparison of the initial distilling 

 temperature. The calculated correction for the emergent stem ther- 

 mometer at 160 is 2, while the actual correction as determined by 

 experiment was never less than 3. These figures show how necessary 

 it is, if comparative data as to the progress of a distillation are desired 

 to have the stem of the thermometer entirely immersed in the vapor, 

 and they also indicate that corrections made under ordinary labora- 

 tory conditions for emergent stem and lag are likely to be inadequate. 



EFFECT OF VARIATIONS IN ATMOSPHERIC PRESSURE. 



Variations in atmospheric pressure may affect the volume of the 

 distillate at any given temperature even more than errors introduced 

 by reading temperatures on emergent thermometers. The effect of 

 variations in pressure on the distillation of two turpentines is shown 

 in the table on page 16. 



