The next process is that of bleaching, because the whiter the cotton cloth becomes, the more light it will reflect from the surface, and the more brilliant the colour of the dyes will appear.
The principal chemical substance used for bleaching cotton is chloride of lime, which is known as bleaching powder; but there are several processes employed in its application, as well as various methods which are adopted by different manufacturers to increase its effects by mechanical contrivances, the application of heat, or otherwise.
Dash Wheel.
The first operation of bleaching, however, and that which immediately follows singeing, is boiling the cloth in an alkaline bath consisting of a solution of soda. For this purpose a bowking apparatus is used. This machine ([see cut]) is, in fact, a large cauldron, with a flat false bottom to protect the cloth from being scorched by the fire beneath. Through the centre of this false bottom a vertical pipe rises from near the real bottom to a height above the top of the cauldron, and carries a conical cap like an umbrella above its open end at top. When the liquid in the cauldron begins to boil thoroughly the steam forces a constant stream of liquid up the pipe, which stream is scattered by forcing against the umbrella-shaped cap, and so falls with some force back on to the cotton in the cauldron. When this process has continued long enough, the liquor is allowed to cool, and the cotton is taken to be rinsed at the dash wheel, where it is subjected to the free action of water, or to a rinsing machine, so constructed that the web travels on rollers, and is thoroughly washed during its course.
Wringing Machine.
The simplest and earliest method of imprinting figures upon calico is by means of a wooden block, upon the face of which the design is cut in relief, as in an ordinary wood-cut. The block is of sycamore, holly, or pear-tree wood, or more commonly of deal, faced with one of these woods. The block varies in size from nine to twelve inches long, and from four to seven inches broad, and it is furnished on the back with a strong handle. When the design is complicated, and a very distinct impression is required, the figure is sometimes formed by the insertion of narrow slips of flattened copper wire, the space between being filled with felt.
