(1) Animal fibres which have to be bleached with peroxide of hydrogen must first be subjected to a treatment which renders them fit to be perfectly soaked with the solution. All fat, suet, and uncleanli-ness must be taken off. The best methods of doing this are soap baths and 3 to 5 per cent, carbonate of ammonia solutions, and in some cases other solvents, such as sulphide of carbon, benzine, ether, etc. For bleaching, the solution of peroxide of hydrogen, which is 3 per cent, by weight, or 10 per cent, by volume, is neutralized by means of a few drops of ammonia, and then used as a bleaching bath. If the bleaching has to be continuous, it is recommended to use several baths of different strengths, in which the goods are passed, beginning from the weaker bath. The light has to be kept off, and the temperature must not rise above 77° F. (25° C). Another method is to dip the cleaned goods in the solution of peroxide of hydrogen, in which they are left until soaked, and are then exposed to dry in a draught, the temperature not to rise above 68° F. (20° C.) The bleaching takes place energetically by the evaporation of the water and subsequent concentration of the peroxide.
(2) The use of bisulphite of soda has proved to be superior to the old method of bleaching in sulphur ovens. The process with the bisulphite requires 6 to 8 hours, and therefore the sulphur bleachers have been slow to adopt it, the sulphur method occupying less time. The following suggestions are made: - Prepare an ordinary dilute solution of soda bisulphite, with the necessary quantity of sulphuric acid, and use the following apparatus, which is on the same principle as that used in the cotton bleaching process in the Barlow kiers. A large cask, with sufficient strength to withstand some steam pressure, is previously filled with thoroughly moistened fibre and tightly pressed in. The prepared solution of soda bisulphite and sulphuric acid, not marking more than 7° Tw. is allowed to enter and soak through the whole lot of fibre; after 5 or 10 minutes' contact, steam is turned on, which presses the solution through the perforated pipe in the centre of the cask and out of the apparatus. The fibre is taken out and aired, by which the bleaching process will not be interrupted; and when nearly dry it is entered a seeond time. Probably 3 or 4 manipulations would suffice to finish the bleaching, and would not occupy more than 2 hours.
The waste liquor is collected, and made up to the first strength for re-use. (' Textile Colourist.').