FLAX STUDIES: II. AN IMPROVED REFRACTOMETRIC METHOD FOR ESTIMATING THE OIL CONTENT OF FLAXSEED

Abstract

The method proposed by Coleman and Fellows, based upon the change in refractive index of halowax, an impure substituted monochlornaphthalene, on dilution with linseed oil extracted from the ground sample, is improved by drying the sample before extraction, grinding in a Hobart mill, filtration for 15 minutes, and the use of a special refractometer with illumination by a 40 watt light. The use of 4 cc. of solvent and extraction at 70 °C. was confirmed. The correlation between halowax extract scale reading and oil content as determined by ethyl ether extraction was 0.95; the standard error of prediction of oil content by the refractometric method was 0.59%. The refractometer readings were not appreciably affected by variations in the refractive index of linseed oil as determined on the ether extract. The correlation between the refractive index and the iodine value of the ether extract was 0.70 with a standard error of prediction of 3.1 units.Further improvement is obtained by the use of a solvent consisting of approximately 50% by volume of halowax and α-bromnaphthalene which gives a standard error of prediction of 0.39%. By slight changes in the proportions, the refractive index of this solvent may be adjusted to a constant value, permitting the use of a permanent conversion chart. Addition of anhydrous sodium sulphate during the extraction obviates the necessity of preliminary drying. With the modifications indicated, the method is suitable for routine determinations on large numbers of samples.