(1) Wetting the woollen material and then rubbing or twisting it. When the fibres are wet, they expand somewhat and the projecting scales, or notches, are loosened. If the material is rubbed at this time, the notched edges interlock.
(2) The use of strong soaps or alkalies. These act chemically on the fibres and soften and expand them, causing the notched edges to become so prominent that they catch in one another.
Note.—The structure of woollen fibres may be sketched on the black-board and compared with those of cotton and linen.
To impress the foregoing principles, a few experiments will be found most useful.
EXPERIMENTS WITH CLOTH MADE OF WOOL FIBRE
1. Boil a piece of new woollen cloth for five minutes. Dry, and compare with an original piece.
2. Saturate a piece of new woollen cloth with a strong solution of washing soda. Dry, and compare with an original piece.
3. Wash a piece of new woollen cloth in each of the following ways:
(1) By rubbing soap directly on the cloth and then sousing the goods in the water.