26 COMMERCIAL TURPENTINES. 



lower-grade varnishes and good quality paints a somewhat colored 

 and slower evaporating product may be successfully employed. In 

 the case of low-grade paints, especially those where the drying is 

 hastened by vigorous means, or in all cases when slow drying is 

 desired, the heavier, slower evaporating turpentine, or even what is 

 known as u pine oil," may prove most suitable. 



METHODS FOB THE EXAMINATION OF TURPENTINE FOB PURITY 



AND QUALITY. 



The work done in connection with this investigation has developed 

 a number of improvements in the methods for examining turpentine 

 which increase the accuracy of the results and insure greater concord- 

 ance in the work of different chemists. The methods to be given 

 have been in use in this laboratory for from one to three years and 

 have been found satisfactory. 



All tests of a turpentine should be promptly made, usually within 

 the same week, because some samples change rapidly in consistency, 

 color, gravity, behavior on distillation, and refractive index, and if 

 the several determinations are made at long intervals those last made 

 may not represent the turpentine as first received. Further, all of 

 the results on a sample may not be strictly comparable and may lead to 

 errors in judging the turpentine. 



COLOR. 



Determine color in a graduated 200 mm tube in a colorimeter 

 reading against the Lovibond yellow glass No. 1. If a depth of 

 200 mm or more is required to match the glass the color is No. 1 ; 

 if a depth of from 100 to 200 mm is required the color is No. 2; if a 

 depth of from 50 to 100 mm is required it is No. 3; and if less than 

 50 mm the color is No. 4. 



SPECIFIC GRAVITY. 



Determine specific gravity with a pyknometer, plummet, Westphal 

 balance, or accurate hydrometer. The determination may be made 

 at 15.5 or at 20 C., as desired. 



DISTILLATION. 



APPARATUS. 



Heating bath. Use a copper cup of about 800 cc capacity, having 

 a concave tight-fitting cover (which may be fixed) with a hole in it 

 large enough to hold a 300 cc distilling flask, and also a one-half inch 

 condensing tube 12 inches long, rising from one side of the cup. 

 This serves as a condenser for the vapors of glycerin or oil used in 

 the bath, and prevents the superheating effect of vapors which would 

 otherwise be in contact with the exposed portion of the distilling 

 flask. 



