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DYEING AND CALICO PRINTING.

entirely different from that of vegetable fibres. It forms, with some solublecolouring materials, genuine compounds or lakes, and adts generally in thisrespedt as do all protein substances. Several salts, including alum, are pre-cipitated by wool from their aqueous solutions, and retained in the wool by aspecial attractive force. Wool has the property, also, of reducing the peroxidesof some of the metals, including iron, to protoxides.

Before wool is ready for the spinner it has to undergo, as already described,a process of washing, in order to remove the dirt accidentally adhering to it,and to eliminate that natural grease which protedts the animal from the chillswhich would be consequent upon the thorough saturation of its coat with rain.As this grease has been found to contain a large quantity of a very pure car-bonate of potassa, Messrs. Maumend and Rogelot have devised a method ofextradting the potassa-salt, so as to obtain from every 1000 kilos, of woolabout 75 kilos, of the carbonate. The method consists in steeping the woolin tepid water (35° to 40°), employing repeatedly the same liquid, and main-taining the heat by the occasional admission of steam when fresh quantitiesof wool are put into the tanks, or rather tubs, wooden vessels being employed.The liquid, when as much saturated with saline matter as possible, is run off,evaporated to dryness, and the residue ignited. The complete elimination offatty matter from the wool is effedted by washing in weak alkaline liquids,partly composed of putrid human urine (carbonate of soda), partly of carbonateof soda.

Bleaching Wool.

The bleaching of woven woollen tissues, or also of woollen yarn (a largeproportion of the wool employed is dyed before weaving), includes numerousoperations, some of which are of a mechanical nature, as, for instance, thefiring or removal by singeing, or in some cases by shaving or shearing off, theloose, downy threads. The woollen fabric is never dyed with the view ofpreserving any part of it white, because affinity of the fibre for colours is sogreat that it takes them without any mordant, and whites therefore could notbe kept clear in dyeing. For this reason, also, the loose hairs on the clothmay be shaven to any degree of closeness.

The bleaching of wool is not a matter of great difficulty, and is far lesslaborious than the bleaching of cotton and linen. From the chemical natureof the wool it will be gathered that it is impossible to apply to it materials ofthe same strength and temperature as are applied to cotton and linen. Theprocess of bleaching wool is a repetition of gentle treatment with soap andvery weak alkalies (carbonates); but when the woollen fabric is required to bedyed with light or bright colours, or is to be printed, the ground must bewhite, and the process of sulphuring resorted to. This was formerly effedledby hanging the moist pieces for several hours in chambers filled with sul-phurous acid gas, or vapours of burning brimstone. It is now performed byMr. Thom’s process, in a few minutes, by passing the goods over a number ofrollers confined in a small chamber filled with the same vapours. Accordingto Mr. Girardin (a great authority in all matters relative to bleaching, dyeing,&c.), M. Pion, at Elbeuf, the seat of an extensive woollen industry in France,obtains excellent results by employing a solution of sulphite of soda acidifiedwith hydrochloric acid, in which the woollen tissues are steeped for somehours, being next thoroughly washed,—an operation equally indispensable after