Page:Popular Science Monthly Volume 56.djvu/317

Rh The material employed is cotton, but whether fresh from the field or in the form of waste, it must first be freed from dirt by hand picking and sorting, and from grease and incrusting substances by boiling in a weak soda solution. The cotton is now dried by wringing in a centrifugal wringer and exposing to a current of hot air in a metal closet; but as the compacted mass of cotton holds moisture with great persistency, after partial drying the cotton is passed through a cotton picker to open the fiber, so that it not only yields its contained water more readily and completely, but it also absorbs the acids more speedily in the dipping process to which it is subsequently exposed.

When the moisture, by the final drying, is reduced to one half of one per cent the cotton is, while hot, placed in copper tanks which close hermetically, where it cools to the atmospheric temperature and in which it is transported to the dipping room, where a battery of large iron troughs, filled with a mixture of one part of the most concentrated nitric acid and three parts of the most concentrated sulphuric acid, set in a large iron water bath to keep the mixture at a uniform temperature, is placed under a hood against the wall. The fluffy cotton, in one-pound lots, is dipped handful by handful under the acid, by means of an iron fork, where it is allowed to remain for ten minutes, when it is raised to the grating at the rear of the trough and squeezed with the lever press to remove

the excess of acid. It still retains about ten pounds of the acid mixture, and in this condition is placed in an acid-proof stoneware crock, where it is squeezed by another iron press to cause the contained acid to rise above the surface of the partly converted