THE STRUCTURE OF COTTON.
(17) The cotton plant is indigenous to many tropical countries, in
which it is often found in a wild state. The product of the wild plant
is, however, quite unsuitable for manufacturing purposes, and, even in
cases where cotton is produced by cultivation, the value of the fibre
varies very largely. Into the question of the growth and structure of
the fibre it is not necessary to go in detail, as this is a subject
which has a literature of its own. The student who is desirous of
obtaining a thorough knowledge of the subject can find it fully treated
in the “Structure of the Cotton Fibre,” by Dr. Bowman, and in a recent
work by Mr. Hugh Monie, jun., of Glasgow. It will suffice for present
purposes to state briefly the characteristics of cotton, which are of
essential importance in its subsequent treatment mechanically. The
cotton fibre is a hollow tube of cellular construction, and is of an
oval or flattened cylindrical shape. Ripe or fully matured fibres of
the best cotton are convoluted or spirally twisted on their axis,
and the edge of such a fibre presents a corrugated appearance. The
regularity of the convolutions, or twists, is greatest in the highest
class of cotton, and reaches its lowest point in the poorer grades.
One important effect of such a formation is that each fibre naturally
tends to coil round its neighbour, and thus lends itself to spinning.
The outer sheath of each fibre is apparently continuous, and the
diameter is greater at the end which is attached to the seed. The
diameter of the fibre varies from 1/1562 of an inch in the case of
Sea Island cotton, to 1/1185 of an inch in Indian cotton. In length a
similar variation is observable, reaching a mean of 1·8 inch in Sea
Island, and being as low as 0·8 inch in Indian cotton. The length of
the fibres in any particular class of cotton is known as the “staple,”
and this is one of the chief commercial merits of the better kinds.
The strength of cotton fibres varies very materially, and on the
authority of Mr. Charles O’Neill, of Manchester, the order in which the
various classes ought to be placed is as follows:—Surat (Comptah), New
Orleans, Queensland, Surat (Dhollerah), Pernambuco, Egyptian, Maranham,
Upland, Sea Island. It does not necessarily follow that the possession
of greater strength by one class of fibre over another involves an
advantage, for the greatest strength is possessed by a fibre which is
the most deficient in regularity of the convolute form and length,
which are much more important than strength. Again, the diameter of
Comptah cotton is much greater than that of longer stapled varieties,
and this is important in determining the value to be placed upon the
strength. Viewed in this light, Egyptian cotton is the strongest,
and this fact, in conjunction with certain other qualities to which
attention will afterwards be called, renders it of high value. It only
remains to be said that a waxy covering is found on the outside of
each fibre, which requires to be softened by heat during spinning so
that the flexibility of the fibre may be fully maintained. Where it
is intended to dye fabrics it is necessary to remove the whole or the
greater part of this wax, and so permit the dye to penetrate the fibre.
Having briefly indicated the chief characteristics of the cotton fibre,
a detailed account of some of the principal varieties may now be given.
(18) Sea Island Cotton. This is the finest class of cotton produced,
being long in the staple, very flexible, and having very regular
convolutions. If care be taken in ginning, so that the fibre is not
broken, the finest yarns can be produced from this variety. The length
of Sea Island Cotton is stated by Dr. Bowman to reach 2·20 inches in
the case of Florida grown, but Mr. Monie states the average length to
be 1·8 inches. Mr. Evan Leigh confirms the higher length, but only in
the case of cotton grown on the Edisto Island. Varieties of this grade
are grown in Peru, Fiji, and Australia, the average lengths being
respectively 1·56, 1·87, 1·65 inches. Fijian Sea Island is spoiled
by bad ginning, which breaks the fibres very much. The colour of Sea
Island cotton is a light creamy one, and is peculiar to it.
(19) Egyptian Cotton. Egyptian cotton varies considerably in colour,
length, and quality. The variety known as Gallini is of a golden
colour, the fibres being tough and strong, and the convolutions very
regular. It has a mean length of 1·5 inch. Brown Egyptian is, as its
name implies, of that colour, and like Gallini, the fibres are strong
and tough, but are coarser, the convolutions are less regular, and the
wall of the fibre is also denser. The mean length is 1·4 inch and the
diameter 1/1325 inch. White Egyptian is, perhaps, the most valuable
of all this class of cotton when properly treated. It is of a light
gold colour, the fibres being strong and pliable, but only partially
spiral. As a result of this, the yarn spun is greater in diameter than
that spun from Gallini (weights being equal), the fibres not lying so
closely together. This cotton mixes well with American and Brazilian.
(20) Brazilian and Peruvian Cotton. Pernambuco cotton is of a slightly
golden colour, and is, comparatively speaking, hard and wiry, being
thus well adapted for twist yarn. The twists in the fibre are well
developed, and the average length is 1·25 inch. Maranham is of a dull
gold colour, mixing well with American cotton. There are several other
varieties of Brazilian cotton, which need not be further referred
to. Rough Peruvian cotton is very clean, of a creamy colour, and is
possessed of an average strength. The fibres are only irregularly
twisted, and an average length is 1·3 inch. The smooth variety is
fairly regularly convoluted, and mixes well with Orleans.
(21) American. There are several varieties of American cotton, which
are grown in the Southern States. Taking them in their order as regards
length of staple, the first to notice is Orleans. The better classes
of this are very uniform in length, clean and light in colour, often
being pure white. One feature of Orleans cotton which renders it very
acceptable to spinners, is that it is very flexible, and possessed of
a high elasticity. In addition to this, as has been previously noted,
its strength is fairly great, and generally its spiral form is well
developed. The average length is about 1 inch. Texas cotton is less
pliable than Orleans, darker in colour, and is not put on the market
so free from immature fibre. Its diameter is greater, and its average
length about equal to Orleans. Upland cotton is clean, and little
waste is produced from it. The fibres are well suited for weft yarns,
being soft and elastic, and of a very light colour. Spun without any
admixture of other cotton, yarns as high as 425’s can be produced, but
when mixed with Egyptian or some other strong fibre, higher counts
can be obtained. Mobile is similar in colour to Orleans, and is equal
to Uplands in strength. It is not so good as either of these for
manufacturing purposes, being much dirtier, and having more flattened
fibres in it.
(22) Indian. The whole of the cottons grown in India are less valuable
than the preceding varieties, owing to the facts that they are not so
regularly spiral, and that the staple is more variable. The highest
class is Hingunghat, which is more convolute than any other Indian
grown cotton. The fibres vary in diameter, but have an average length
of 1·03 inch. Broach is brownish gold in colour and is fairly clean,
although it is not thoroughly cleaned, and contains a good deal of leaf
and nep. It is about 0·9 inch long, and is more regular in this respect
than Hingunghat. The spirals are fewer in number, and it is stated by
Mr. Monie that the walls are very liable to rupture. Dhollerah is of a
white colour, and is best adapted for weft yarn. Oomrawuttee is creamy
in colour, being strong but rather short in the staple. A good deal of
impurity is found in this quality, but the convolute form is moderately
developed. Tinnivelly is grown in the Madras Presidency, and is a
fairly good cotton. In strength it is high and is very elastic, its
colour being a dull, creamy one. The fibres have a small bore and thick
walls, and are, in addition, only slightly twisted. The worst Indian
fibre is Bengal, which is short, strong, and dirty.
(23) Commercial qualities. The recapitulation of the principal features
of various growths of cotton just given enables their relative value
for spinning to be pointed out, and at the same time to indicate the
qualities it is desirable to retain during the subsequent mechanical
treatment. Sea Island cotton is beyond doubt the finest quality
existing, and, in the manufacture of fine counts, is absolutely
essential. Its general excellence is undoubtedly attributable to the
conditions under which it is grown, and even this might be improved by
more careful cultivation. Egyptian cotton is also of great value in the
production of good yarns, and is very largely used for this purpose.
Owing to the existence of a number of short fibres, always found in
commercial quantities, but present here in larger proportion, it is
necessary to comb all Egyptian cotton. The chief advantage of its use
is that being relatively stronger, smoother surfaced, and more flexible
than qualities other than Sea Island, a large range of yarns for
various uses can be spun at a price which enables them to be profitably
used. The fibres are very regular in diameter, and when twisted lie
very close together. The most widely used cotton is, however, the
various brands of American, which have the advantage of careful
attention during their growth and collection. In consequence of this,
there is a very high uniformity attained, together with great freedom
from all sorts of impurities, these two qualities rendering American
cotton highly suited for general use. Indian cotton is coarser,
harsher, and not so clean as other varieties, and requires greater
care in its manufacture. Summing up, the desirable points in cotton
are the length and regular convolute form of the fibre, together with
its freedom from mechanical and chemical impurities. The object of the
earlier mechanical processes through which cotton passes is to remove
all the impurities, lay the fibres regularly and in equal numbers
alongside each other, without breaking or rupturing them, and without
destroying their natural tendency to twist round each other. In doing
this, not merely do the seeds, leaf, and sand require removal, but
also the short immature fibres which form into little knots or tangles
called “neps.” Great care is needed in the preparatory stages so as to
avoid damage, and it is especially necessary to avoid the removal of
the waxy sheath which plays an important part in the manufacture of
the fibre. The necessity for a warm, humid atmosphere has already been
referred to, but it may be noted that it is very important on account
of its softening effect upon the waxy sheath. If the latter be removed
the heat becomes a source of difficulty instead of a help, as the
natural moisture existing in the fibre is more speedily absorbed.