class="col10">Oxygen 20·5 " 21·2 "
Sulphur 5·4 " 2·3 "
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100·00 100·00

It is sometimes stated that wool fibre consists of a definite substance, keratine, but this view cannot now be admitted, since wool appears to be composed of a mixture or combination of several very complex substances. It is possible and even probable that the outer epidermal scales have a somewhat different composition to the bulk of the fibre, but whether that is the case or not is not known with any degree of certainty, this much can be asserted, that wool is not a simple definite chemical compound.

Sulphur is by far the most variable constituent of wool, sometimes as little as 1·5 and occasionally as much as 5 per cent. being found. It appears to be always present in two different forms, one portion being in very feeble combination and easily removed by alkalies, the remainder, which, according to Knecht, amounts to about 30 per cent. of the total sulphur, cannot be removed without complete disintegration of the fibre. This latter portion does not give a black coloration with plumbite of soda.

The amount of ash left on incinerating dry wool varies from 1 to 2 per cent., and some have considered this inorganic matter as an essential constituent. It consists principally of salts of potassium, calcium and aluminum, with, of course, sulphur.

The chemical composition of the wool fibre is evidently of a most complicated nature; judging from its behaviour in dyeing it is evident that it may contain two bodies, one of a basic character which enables it to combine with the azo and acid series of dyes, the other possessing acid characters enabling it to combine with the basic dyes of the magenta and auramine type. Dr. Knecht has isolated from the wool fibre by extraction with alkalies and precipitation with acids a substance to which the name of lanuginic acid has been given. It is soluble in hot water, precipitates both acid and basic colouring matters in the form of coloured lakes. It yields precipitates with alum, stannous chloride, chrome alum, silver nitrate, iron salts, copper sulphate. It appears to be an albuminoid body. From its behaviour with the dyes, and with tannic acid and metallic salts, it would appear that lanuginic acid contains both acidic and basic groups. It contains all the elements, carbon, hydrogen, oxygen, nitrogen and sulphur, found in wool.

If wool is dyed in a dilute solution of Magenta (hydrochloride of rosaniline), the whole of the base (rosaniline) is taken up, and the whole of the acid (HCl) left in the bath, not, however, in the free state, but probably as NH₄Cl, the ammonia being derived from the wool itself. A further proof of the acid nature of lanuginic acid is that wool may be dyed a fine magenta colour in a colourless solution of rosaniline base; for since rosaniline base is colourless, and it only forms a colour when combined with acids, the fibre has evidently acted the part of an acid in the combination.

Chemical Properties. Action of Alkalies.--Alkalies have a powerful action on wool, varying, of course, with the nature of the alkali, strength of solution and temperature at which the action takes place.

An ammoniacal solution of copper hydroxide (Schweizer's reagent), has comparatively little action in the cold, but when hot it dissolves wool fairly readily.

The caustic alkalies; sodium hydroxide, NaOH, or potassium hydroxide KOH, have a most deleterious action on wool. Even when very dilute and used in the cold they act destructively, and leave the fibre with a harsh feel and very tender, they cannot therefore be used for scouring or cleansing wool. Hot solutions, even if weak, have a solvent action on the wool fibre, producing a liquid of a soapy character from which the wool is precipitated out on adding acids.

This action of alkalies has an important bearing on the scouring of wool, for if this operation be not carried out with due care there is in consequence great liability to impair the lustre and strength of this fibre. From microscopical examination this effect of alkalies is seen to be due to the fact that they tend to disintegrate the fibre, loosen and open the scales, this is shown by contrasting the two fibres A and B shown in figure 4, A being a normal wool fibre, B one strongly treated with an alkali.

The alkaline carbonates have but little action on wool, none if used dilute and at temperatures below 120° F.

Soap has practically no action on wool, and is therefore an excellent scouring material for wool. The carbonate of ammonia is the best and has the least action of the alkaline carbonates, those of potash and soda if used too strong or too hot have a tendency to turn the wool yellow, the carbonate of potash leaves the wool softer and more lustrous than the carbonate of soda.

The influence of scouring agents on wool will be discussed in the chapter on cleansing wool fabrics in more detail.

Caustic or quick-lime has a similar injurious action on the wool fibre as the caustic alkalies.

Action of Acids.--Acids when dilute have but little influence on the wool fibre, their tendency is to cause a separation of the scales (see fig. 5) of the wool and so make it feel harsher. Strong acids have a disintegrating action on the wool fibre. There is a very considerable difference between the action of acids on wool and on cotton, and this difference of action is taken advantage of in the woollen industry to separate cotton from wool by the process commonly known as "carbonising," which consists in treating the fabric with a weak solution of hydrochloric acid or some other acid, then drying it; the cotton is disintegrated and falls away in the form of a powder, while the wool is not affected, sulphuric acid is used very largely in dyeing wool with the acid- and azo-colouring matters.

Nitric acid affects wool in a very similar manner to the acids named above when used in a dilute form; if strong it gives a deep yellow colour and acts somewhat destructively on the fibre.

Sulphurous acid (sulphur dioxide) has no effect on the actual fibre, but exercises a bleaching action on the yellow colouring matter which the wool contains, it is therefore largely used for bleaching wool, being applied either in the form of gas or in solution in water; the method will be found described in another chapter. Wool absorbs sulphur dioxide in large amount, and if present is liable to retard any subsequent dyeing processes.

Action of Other Substances.--Chlorine and the hypochlorites have an energetic action on wool, and although they exert a bleaching action they cannot well be used for bleaching wool. Hot solutions bring about a slight oxidation of the fibre, which causes it to have a greater affinity for colouring matters; advantage is taken of this fact in the printing of delaines and woollen fabrics, while the woollen dyer would occasionally find the treatment of