TURPENTINE. 495 
(e) Refractive index.—Determine refractive index at 20° C. with an accurate 
instrument. When the refractive index is determined at any other temperature, the 
readings obtained shall be corrected to 20° C. by adding to or by subtracting from the 
actual reading 0.00045 for each degree centigrade that the temperature at which the 
determination was made is, respectively, above or below 20° C. 
(f) Distillation.—Apparatus.!—Condenser.—The type of apparatus (fig. 6) adopted 
as by the American Society for Testing Materials for the distillation of paint thinners 
other than turpentine, substituting for the thermometer there described an im- 
mersed thermometer such as is described below, is preferred. In case the A. 8. 
T. M. distillation apparatus is not available, use an ordinary straight glass-tube con- 
denser, about 22 inches long, with 16 inches in contact with the cooling water. The 
end of the condenser tube should be fitted with an adapter or should be bent down toa 
i 
ey 
Bed 
-—-> 
[ 
Fiaq. 6.—Distillation apparatus. 
néarly vertical position, and the tip should be cut off or ground down atan acute angle. 
The tip should extend a short distance into the receiving cylinder. 
Flask.—Comparable results can be obtained only by using flasks of the same dimen- 
sions. The distilling flask used shall be the standard Engler flask, as used for petro- 
leum distillation, having the following dimensions: Diameter of bulb, 6.5 cm.; 
cylindrical neck, 15 cm. long, 1.6 cm. internal diameter; side or vapor tube, 10 cm. 
long, 0.6 cm. external diameter, attached to neck at an angle of 75°, so that when the 
‘7! flask contains its charge of 100 cc. of oil the surface of the liquid shall be 9 cm. below 
the bottom of the junction of the side tube and neck. 
Support for flast.—Support the flask on a plate of asbestos 20 cm. in diameter, 
having an opening 4 cm. in diameter in its center, and heat with an open flame. 
Surround the flask and burner with a shield to prevent fluctuation in the temperature 
of the neck of the flask. Or, support the flask in a metal cup, 15 to 20 cm. in diameter, 
1A.S. T. M. Standards (1918), p. 607. 
