Wool Scouring by Solvents.--Of late years processes have been invented for the scouring of wool, either raw or spun by means of solvents, like carbon bisulphide, benzol, petroleum spirit, etc. Such processes are in a sense rather more scientific than the alkali processes, for whereas in the latter the grease, etc., of the wool and the oil used in batching it are practically lost for further use, and therefore wasted, being thrown away very often, although they may be partially recovered from the used scouring liquors, in the solvent processes the grease and oil may be recovered for future use for some purpose or other.
The great objection to these processes is the danger that attends their use, owing to the inflammable character of the solvents. Several other objections may be raised, some of which are mechanical, and due to the want of proper machinery for carrying out the processes. There are many ways in which solvents may be applied, some are the subject of patents. It is not possible to describe the details of all these, but two of the most recent will be mentioned.
In Singer's process, which was described in detail by Mr. Watson Smith some time ago before the Society of Dyers and Colourists, carbon bisulphide is used. The raw wool is placed between two endless bands of wire, and it is carried through a series of troughs containing bisulphide of carbon; during its passage through the troughs the solvent takes out the grease, and loosens the other constituents of the wool. After going through the bisulphide the wool is dried and passed through water which completes the process. The carbon bisulphide that has been used is placed in steam-heated stills, distilled off from the grease, condensed in suitable condensers, and used over again. In this process, with care, there is very little loss of solvent. The grease which is recovered can be used for various purposes, one of which is the manufacture of ointments, pomades, etc. The disadvantages of bisulphide are: (1) It tends after some time to cause the wool to acquire a yellow cast, due to the free sulphur which it contains, and which being left in the wool gradually causes it to turn yellow. By using redistilled bisulphide this defect may be avoided. (2) Another defect is the evil odour of the solvent. This, however, is less with redistilled bisulphide than with the ordinary quality, and with suitable apparatus is not insuperable. (3) Another defect is the volatility and inflammability of carbon bisulphide. On the other hand, bisulphide possesses the very great advantage of being at once heavier than, and insoluble in, water, and it can be, therefore, stored under water very much more safely than can any of the other solvents which are used.
Burnell's machine has two troughs filled with benzoline. In these are arranged a large central roller round which are some smaller rollers. The wool passes round the large roller and is subjected to a number of squeezings in passing the smaller rollers. A current of the benzoline is continually passing through the machine. The whole is enclosed in a hood to avoid loss of solvent as far as possible. After passing through the benzoline trough the wool passes through a similar trough filled with water. Benzoline is better than carbon bisulphide in that there is no tendency on the part of the wool to turn yellow after its use, on the other hand it is more inflammable, and when it does take fire is more dangerous, and being lighter than water is not so readily and safely stored. Another feature is that it is not so completely volatile at steam temperatures, so that a little may be left in the grease and thus tend to deteriorate it. Coal-tar benzol, the quality known as 90's, would be better to use.
The solvent processes are well worth the attention of wool scourers, all that is required for their proper development being the production and use of suitable machinery.
After the raw wool has been scoured it is batched, i.e., it is mixed with a quantity of oil for the purpose of lubricating the wool to enable it more easily to stand the friction to which it is subjected in the subsequent processes of spinning and weaving by giving it greater pliability.
For this purpose various kinds of oil are used. Olive oil is the principal favourite, the variety mostly used being Gallipoli oil. Ground-nut oil is also extensively employed, and is cheaper than olive. Oleic acid a by-product of the candle industry, is extensively used under the name of cloth oil, there is also used oleine, or wool oil, obtained by the distillation of Yorkshire grease.
So far as merely oiling the wool is concerned there is not much to choose between these different oils, olive perhaps works the best and agrees best with the wool. Mineral oils have been and can be used either alone or mixed with the oils above mentioned, and so far as lubricating the wool is concerned do very well and are much cheaper than the fatty oils named above.
The following are some analyses of various oils used as cloth oils which the author has had occasion to analyse.
| 1. | 2. | 3. | 4. | |
| Specific gravity at 60° F. | 0·9031 | 0·9091 | 0·6909 | 0·8904 |
| Free fatty acid | 55·02 | 64·42 | 51·52 | 68·05 |
| Unsaponifiable oil | 34·56 | 9·95 | 32·80 | 9·52 |
| Saponifiable oil | 10·32 | 25·32 | 15·68 | 12·43 |
| ------ | ------ | ------ | ------ | |
| 100·00 | 100·00 | 100·00 | 100·00 |