194 
BUIvLETIN OB THB BUREAU OP FISHERIES. 
INDEX OF refraction. 
The refractive indices were measured by the use of a microscope, the apparent and 
true depths of a column of liquid being compared. Figure 6 shows that the index of 
refraction is not a good criterion of the purity of linseed and soya-bean oils when being 
tested for the presence of fish oil, but it should be valuable in the case of China-wood oil. 
/^e/racr/o/7 
the refractive index of which is considerably greater than that of the other oils. This 
has been brought out by the work of Wise® in a recent study of this oil. 
ACID, SAPONIFICATION, AND IODINE NUMBERS. 
The results of the acid, saponification, and iodine number measurements are pre- 
sented in table ix and figures 7 to 9. The first two numbers represent the milligrams 
of potassium hydroxide necessary for i gram of oil, while the iodine numbers were 
obtained by Hiibl’s method, being per cent iodine required by the oil. 
« Wise. L. E.: On the indices of refraction of China-wood oil. Journal of Industrial and Engineering Chemistry, vol. 4, 
1912, p. 497-498. Easton, Pa. 
