look like
flax, but, as we shall see, it is not chemically identical with cotton,
as linen or flax is. Another vegetable fibre, termed "cotton-silk," from
its beautiful, lustrous, silky appearance, has excited some attention,
because it grows freely in the German colony called the Camaroons, and
also on the Gold Coast. This fibre, under the microscope, differs
entirely in appearance from both cotton and flax fibres. Its fibres
resemble straight and thin, smooth, transparent, almost glassy tubes,
with large axial bores; in fact, if wetted in water you can see the
water and air bubbles in the tubes under the microscope. A more detailed
account of "cotton-silk" appears in a paper read by me before the
Society of Chemical Industry in 1886 (see _J.S.C.I._, 1886, vol. v. p.
642). Now the substance of the cotton, linen or flax, as well as that of
the cotton-silk fibres, is termed, chemically, cellulose. Raw cotton
consists of cellulose with about 5 per cent. of impurities. This
cellulose is a chemical compound of carbon, hydrogen, and oxygen, and,
according to the relative proportions of these constituents, it has had
the chemical formula C_{6}H_{10}O_{5} assigned to it. Each letter
stands for an atom of each constituent named, and the numerals tell us
the number of the constituent atoms in the whole compound atom of
cellulose. This cellulose is closely allied in composition to starch,
dextrin, and a form of sugar called glucose. It is possible to convert
cotton rags into this form of sugar--glucose--by treating first with
strong vitriol or sulphuric acid, and then boiling with dilute acid for
a long time. Before we leave these vegetable or cellulose fibres, I will
give you a means of testing them, so as to enable you to distinguish
them broadly from the animal fibres, amongst which are silk, wool, fur,
and hair. A good general test to distinguish a vegetable and an animal
fibre is the following, which is known as Molisch's test: To a very
small quantity, about 0.01 gram, of the well-washed cotton fibre, 1 c.c.
of water is added, then two to three drops of a 15 to 20 per cent.
solution of alpha-naphthol in alcohol, and finally an excess of
concentrated sulphuric acid; on agitating, a deep violet colour is
developed. By using thymol in place of the alpha-naphthol, a
red or scarlet colour is produced. If the fibre were one of an animal
nature, merely a yellow or greenish-yellow coloured solution would
result. I told you, however,