With two or three important exceptions the dispersion values of oils lie too close together for use in analyses. The most interesting results were obtained with Tung Oil and Coconut Oil. In America Holley and Brier's method, which is stated to have been in successful use for the last six years, is not based directly on the numerical values for the dispersion but depends on the inversion of the spectrum colours shown by Tung Oil when examined in the Pulfrich Refractometer. An addition of not less than 15 per cent. of pure Linseed Oil to the Tung Oil under examination should restore the normal position of the colour bands. If less than 15 percent, is required, the oil is considered adulterated, while very pure oils have required as much as 22 per cent.; the quality varies in different years. (Holley, Paint Vehicles, Japans and Varnishes, 1920.) As, however, Fryer & Weston point out in their important communication on the "Dispersion of Oils," Analyst, 1918, pages 311-317, it should be preferable to measure the dispersion. The Abbe Refractometer can be used for this purpose, although the Pulfrich, of course, gives more accurate readings.

Szalágyi's measurements (Ref. No. 453) of the dispersion of commercial oils in 1914 were followed, in 1918, by Fryer & Weston's work, in which the selection of the samples was carefully made, and their figures are, in the present writer's opinion, to be adopted when they differ from the earlier figures.

Fryer & Weston show the effect of oxidisation and heating on the dispersion, and also the effect of Fatty Acids; some of their results are tabulated below. It should be pointed out, however, that Szalágyi finds that the dispersion of the Fatty Acids of Castor Oil is lower than the dispersion of the oil, while, in the case of Niger Seed Oil and Almond Oil, Fryer & Weston found that the Fatty Acids gave slightly higher values.

J. N. G.

Fryer & Weston Dispersion At 40&Deg; C. SzalÁYi Dispersion At 45&Deg; C