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, that jute is not chemically identical with cotton and linen.  The substance of its fibre has been termed “bastose” by Cross and Bevan, who have investigated it.  It is not identical with ordinary cellulose, for if we take a little of the jute, soak it in dilute acid, then in chloride of lime or hypochlorite of soda, and finally pass it through a bath of sulphite of soda, a beautiful crimson colour develops upon it, not developed in the case of cellulose (cotton, linen, etc.).  It is certain that it is a kind of cellulose, but still not identical with true cellulose.  All animal fibres, when burnt, emit a peculiar empyreumatic odour resembling that from burnt feathers, an odour which no vegetable fibre under like circumstances emits.  Hence a good test is to burn a piece of the fibre in a lamp flame, and notice the odour.  All vegetable fibres are easily tendered, or rendered rotten, by the action of even dilute mineral acids; with the additional action of steam, the effect is much more rapid, as