_Linseed_, _Flax Seed_; F. _Semence de Lin_; G. _Leinsamen_,
_Flachssamen_.
=Botanical Origin=—_Linum usitatissimum_ L., Common Flax, is an annual
plant, native of the Old World, where it has been cultivated from the
remotest times. It sows itself as a weed in tilled ground, and is
now found in all temperate and tropical regions of the globe. Heer
regards it as a variety evolved by cultivation from the perennial _L.
angustifolium_ Huds.
=History=—The history of flax, its textile fibre and seed, is
intimately connected with that of human civilisation. The whole process
of converting the plant into a fibre fit for weaving into cloth is
frequently depicted on the wall-paintings of the Egyptian tombs.[391]
The grave-clothes of the old Egyptians were made of flax, and the use
of the fibre in Egypt may be traced back, according to Unger,[392] as
far as the 23rd century B.C. The old literature of the Hebrews[393]
and Greeks contains frequent reference to tissues of flax; and fabrics
woven of flax have actually been discovered together with fruits
and seeds of the plant in the remains of the ancient pile-dwellings
bordering the lakes of Switzerland.[394]
The seed in ancient times played an important part in the alimentation
of man. Among the Greeks, Alcman in the 7th century B.C., and the
historian Thucydides, and among the Romans Pliny, mention linseed
as employed for human food. The roasted seed is still eaten by the
Abyssinians.[395]
Theophrastus expressly alludes to the mucilaginous and oily properties
of the seed. Pliny and Dioscorides were acquainted with its medical
application both external and internal. The latter, as well as
Columella, exhaustively describes flax under its agricultural aspect.
In an edict of the Emperor Diocletian _De pretiis rerum venalium_[396]
dating A.D. 301, linseed is quoted 150 _denarii_, sesamé seed 200, hemp
seed 80, and poppy seed 150, the _modius castrensis_, equal to about
880 cubic inches.[397] The propagation of flax in Northern Europe as of
so many other useful plants was promoted by Charlemagne.[398] It seems
to have reached Sweden and Norway before the 12th century.[399]
[391] Wilkinson, _Ancient Egyptians_, iii. (1837) 138, &c.
[392] _Sitzungsberichte der Wiener Akademie_, Juni 1866.
[393] Exod. ix. 31; Lev. xiii. 47, 48; Isaiah xix. 9.
[394] Heer in Trimen’s _Journ. of Bot._ i. (1872) 87.
[395] A. de Candolle, _Géogr. Botanique_, 835.—A. Braun, _Flora_, 1848.
94.
[396] See p. 65, note 1.
[397] The English _imperial gallon_ = 277·27 cubic inches.
[398] For further historical information on flax in ancient times, we
may refer to Hehn, _Kulturpflanzen und Hausthiere ..._ Berlin, 1870.
97, 430.
[399] Schübeler, _Die Pflanzenwelt Norwegens_, Christiania, 1873-1875.
p. 332.
=Description=—The capsule which is globose splits into 5 carpels,
each containing two seeds separated by a partition. The seeds are of
flattened, elongated ovoid form with an acute edge, and a slightly
oblique point blunt at one end. They have a brown, glossy, polished
surface which under a lens is seen to be marked with extremely fine
pits. The hilum occupies a slight hollow in the edge just below the
apex. The testa which is not very hard encloses a thin layer of
albumen surrounding a pair of large cotyledons having at their pointed
extremity a straight embryo. The seeds of different countries vary
from ¼ to ⅙ of an inch in length, those produced in warm regions being
larger than those grown in cold. We find that 6 seeds of Sicilian
linseed, 13 of Black Sea and 17 of Archangel linseed weigh respectively
_one grain_.
When immersed in water, the seeds become surrounded by a thin,
slippery, colourless, mucous envelope, which quickly dissolves as a
neutral jelly, while the seed slightly swells and loses its polish. The
seed when masticated has a mucilaginous oily taste.
=Microscopic Structure=—On examining the testa under almond oil or oil
of turpentine, the outlines of the epidermal cells are not distinctly
visible. But under dilute glycerin or in water the epidermis quickly
swells up to 3 or 4 times its original thickness; on warming, the
entire epidermis is resolved into mucilage, except a thin skeleton
of cell-walls, which withstands even the action of caustic lye. The
formation of the mucilage may be conveniently studied by the use of a
solution of ferrous sulphate, with which thin sections of the testa
should be moistened. Other structural peculiarities may be seen if they
are imbued with concentrated sulphuric acid, washed and then moistened
with a solution of iodine. The application of polarized light is also
useful. By the latter means crystalloid granules of albuminoid matter
become visible if the sections are examined under oil. The tissue of
the albumen and the cotyledons abounds in drops of fatty oil.
=Chemical Composition=—The constituent of chief importance is the fixed
oil which the seed contains to about ⅓ of its weight. The proportion
obtained by pressure on a large scale is 20 to 30 per cent. varying
with the quality of the seed. The oil when pressed without heat and
when fresh has but little colour, is without unpleasant taste, and does
not solidify till cooled to -20° C. The commercial oil however is dark
yellow, and has a sharp repulsive taste and odour. On exposure to the
air, especially after having been heated with oxide of lead, it quickly
dries up to a transparent varnish consisting chiefly of _Linoxyn_,
C₃₂H₅₄O₁₁. The crude oil increases in weight 11 to 12 per cent.,
although at the same time its glycerin is destroyed by oxidation.
By saponification, linseed oil yields glycerin, and 95 per cent.
of fatty acids, consisting chiefly of _Linoleic Acid_, C₁₆H₂₆O₂,
accompanied by some oleic, palmitic, and myristic acid. The action
of the air transforms linoleic acid into the resinoid _Oxylinoleic
Acid_, C₁₆H₂₆O₅. Linoleic acid appears to be contained in all drying
oils, notably in that of poppy seed. It is not homologous either
with ordinary fatty acids or with the oleic acid of oil of almonds,
C₁₈H₃₄O₂. The chemistry of the drying oils, especially those of linseed
and poppy, has been particularly investigated by Mulder.[400]
The viscid mucilage of linseed cannot be filtered till it has been
boiled. It contains in the dry state more than 10 per cent. of mineral
substances, when freed from which and dried at 110° C. it corresponds,
like althæa-mucilage, to the formula C₁₂H₂₀O₁₀. The seeds by exhaustion
with cold or warm water afford of it about 15 per cent. By boiling
nitric acid it yields crystals of mucic acid; by dilute mineral acids
it is broken up into dextrogyre gum and sugar and cellulose.[401]
Linseed contains about 4 per cent. of nitrogen corresponding to about
25 per cent. of protein-substances. After expression of the oil these
substances remain in the cake so completely that the latter contains
5 per cent. of nitrogen, and constitutes a very important article for
feeding cattle.
In the ripe state linseed is altogether destitute of starch, though
this substance is found in the immature seed in the very cells which
subsequently yield the mucilage. The latter may be regarded as in
analogous cases to be a product of the transformation of starch.
The amount of water retained by the air-dry seed is about 9 per cent.
The mineral constituents of linseed, chiefly phosphates of potassium,
magnesium, and calcium, amount on an average to 3 per cent., and
pass into the mucilage. By treating thin slices of the testa and its
adhering inner membrane with ferrous sulphate, it is seen that this
integument is the seat of a small amount of tannin.
=Production and Commerce=—Flax is cultivated on the largest scale in
Russia, from which country there was imported into the United Kingdom
in 1872 linseed to the value of 3 millions sterling. The shipments were
made in about equal proportion from the northern and the southern ports
of Russia.
The imports from India in the same year amounted in value to
£1,144,942, and from Germany and Holland to £144,108. The total import
in 1872 was 1,514,947 quarters, value £4,513,842.
The cultivation of flax in Great Britain appears to be declining. The
area under this crop in 1870 was 23,957 acres; in 1871, 17,366 acres;
in 1872, 15,357 acres; and in 1873, 14,683 acres. The last named
area reckoning the yield at 2 to 2½ quarters of seed per acre would
represent a production of about 30,000 to 38,000 quarters.
[400] His numerous investigations on this subject have been published
in a separate pamphlet, of which we have before us a German
translation: G. J. Mulder, _Die Chemie der austrocknenden Oele_ ...
Berlin, 1867, pp. 255.
[401] Kirchner and Tollens, _Annalen der Chemie_, 175 (1874) 215.
In English price-currents, eight sorts of linseed are enumerated,
namely, English, Calcutta, Bombay, Egyptian, Black Sea and Azof,
Petersburg, Riga, Archangel. The first three appear to fetch the
highest prices.
=Uses=—In medicine, linseed is chiefly used in the form of poultice
which may be made either of the seed simply ground or of the pulverized
cake. In either case the powder should not be long stored, as the oil
in the comminuted seed is rapidly oxidized and fatty acids produced.
An infusion of the seeds called _Linseed Tea_ is a common popular
demulcent remedy.
=Adulteration=—Linseed is very liable to adulteration with other seeds,
especially when the commodity is scarce. The admixture in question
is due in part to careless harvesting and in part to intentional
additions. In 1864 the impure condition of the linseed shipped to
the English market had become so detrimental to the trade that the
importers and crushers founded an association called _The Linseed
Association of London_, by which they bound themselves to refuse all
linseed containing more than 4 per cent. of foreign seeds, and this
step very rapidly improved the quality of the article.[402]
[402] Greenish in _Yearbook of Pharmacy_, 1871. 590; _Pharm. Journ._
Sept. 9, 1871. 211.
As the druggist has to _purchase_ linseed meal, he must of necessity
rely to some extent on the character of the oil-presser from whom he
derives his supplies. The presence of the seeds of _Cruciferæ_ (as
rape and mustard) which is common, may be recognized by the pungent
odour of the essential oil which they develope in contact with water.
The introduction of cereals would also be easily discovered by iodine,
which strikes no blue colour in a decoction of linseed. The microscope
will also afford important aid in the examination of linseed cake or
meal.