Linseed - Linum usitatissimum -
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Constituents---The envelope or testa of the seed contains about 15 per cent of mucilage. The seeds themselves contain in the cotyledons and endosperm from 30 to 40 per cent of a fixed oil, of a light yellow colour, and about 25 per cent proteids, together with wax, resin, sugar, phosphates, acetic acid, and a small quantity of the glucoside Linamarin. On incineration, linseed should not yield more than 5 per cent of ash.
The oil is obtained by expression, with little or no heat. The cake which remains after expressing the oil, and which contains the farinaceous and mucilaginous part of the seed, is familiarly known as oil-cake, and is largely used as a fattening food for cattle. It is also used as a manure. When ground up, it is known as linseed meal, which is employed for making poultices. The meal is sold in two forms, crushed linseed and linseed meal. Formerly linseed meal was always obtained by grinding English oil-cake to powder and contained little oil, but now the crushed seeds, containing all the oil, are official. Crushed linseed of good quality usually contains from 30 to 35 per cent of oil.
Linseed oil rapidly absorbs oxygen from the air and forms, when laid on in thin layers, a hard, transparent varnish. It is largely used in the arts for its properties as a drying oil. It is a viscid, yellow liquid, its chief constituent being Linolein. It also contains palmitin, stearin and myristin, with glyceride of linoleic acid. Boiled oil, produced by heating raw linseed oil to a temperature of 150 degrees C. , together with a small proportion of a metallic drier, possesses the drying properties of linseed oil to an enhanced degree. It becomes of a brown colour and dries much more rapidly, and in this state is used in the manufacture of printer's ink.