Linseed Oil

Linseed oil is obtained from the seed of the common cultivated flax (Linum usitatissimum). Linseed varies in size and colour. The usual colours are a purplish-brown and a reddish-brown, but there is a nearly white sort - a mere sport or variety - which may be said to be straw-coloured. It is grown along with the brown variety in some parts of the North-West Provinces of India, particularly in Nagpur, but no pains are taken to keep the strain pure. Through the kind offices of the Director of the Royal Gardens, Kew, the Government of India were good enough to obtain a specially pure sample of some hundredweights of white Nagpur linseed, and to place it at my disposal. Attempts to grow it for seed in this country and in Belgium failed, but a large quantity of oil was expressed for trial and analysis. Messrs. Bell and Co., of 225, Oxford Street, obtained several gallons of oil by cold-pressure; many artists have expressed their approval of the product. One advantage of this white seed is the ease with which the purity of a sample may be recognised by the eye, any accompanying weed-seeds differing widely in colour from the white linseed.

The skin of the seed is, moreover, thin, the cold-drawn oil is nearly colourless, and the seed is particularly rich in oil, containing no less than 45 percent of its weight, although, of course, much less than this proportion is obtainable by cold-pressure. In a hand-press about 25 percent was the average yield. Of the common or brown linseed our chief supplies come from Russia and India. The Russian seed is generally finer than the East Indian; it is, moreover, imported in a less mixed and impure condition. By screening, the greater part of the impurities are or may be removed, but it is sold on a basis of 4 percent impurity. The impurities consist of dirt, other oil-seeds, such as mustard, rape, and gold of pleasure, and non-oily weed-seeds. The presence of the last-named, though it reduces the yield, is not otherwise objectionable,¹ but the same remark does not apply to the foreign oil-seeds. Most of these contain non-drying oils, which mingle with the linseed oil when the sample is pressed and reduce its siccative character. Much linseed now comes from Argentina, Canada, and the United States, as well as from India and Russia.

1	Occasionally these weed-seeds give up, under pressure, certain matters which deepen the colour of the expressed oil somewhat.