12 



WOOD TUKPENTINES. 



widely variable character. However, ordinary intelligence and a 

 little experience are sufficient to indicate the proper variations in 

 detail. 



EXAMINATION OF FRACTIONS. 



The weight of each fraction is determined and the percentage 

 weights of each fraction and of the total combined fractions (see 

 Table 1) are then computed. The maximum boiling point of each 

 fraction is read from the thermometer at the top of the column, and 

 the specific gravity and index of refraction of each fraction and of 

 the residue left in the flask are determined. 



TABLE 1. Typical data sheet showing records of distillations. 



Boiling point. The boiling temperatures as read should be cor- 

 rected (1) for the prevailing barometric pressure, using the factor 

 0.056 for every millimeter difference from the normal, 760 mm., and 

 (2) for the emergent stem of the thermometer according to the follow- 

 ing formula : * To the observed value of the boiling point, T, should 

 be added the factor 0.000143 (T-t) N, in which t is the temperature 

 of the thermometer stem above the cork and N the length expressed 

 in degrees of the mercury column above the cork. 



1 Young's " Fractional Distillation," p. 12. 



