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 (p. 025) 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.