(a) For bleaching rags, and other materials from which paper is at first fabricated, rags, when grey or coloured, are to be separated and ground in the paper-mill in the usual way, till brought to a sort of uniform consistence, having been previously macerated according to their quantity and tenacity. The mass is then treated with an alkaline lye. It is next treated with a solution of chloride of lime. If this immersion do not produce the desired effect, which does not often happen if the colours are tenacious, such as red and blue, let the treatment with the alkaline lye be repeated, and follow it with another bath of the chlorine preparation. Then sour the whole in a bath of sulphuric acid, much diluted and cold for when hot its action will be less effectual. Water is then to be run upon it till it comes off without colour or indication of acidity. Black is the most easily discharged colour, and will seldom require being treated with lye or steep of sulphuric acid, one bath of alkali and another of chloride of lime being sufficient to produce a good white.
(6) Old printed or written paper is first sorted according to its quality, and all the yellow edges cut off with a bookbinder's plane. One hundredweight of this paper is put sheet by sheet into rats sufficiently capacious, with 500 quarts of hot water. The whole is stirred for about an hour, and as much water gradually added as will rise about three inches above the paper, and left to macerate for four or five hours. It is then ground coarsely in the mill, and boiled In water for about an hour, taking care to add before it begins to boil, 13 quarts of caustic alkaline lye. After boiling, it is macerated in the lye for 12 hours, when it is pressed, and, if sufficiently white, made into paper.
(c) Paper which has been very imperfectly bleached may be rendered thoroughly white by pouring upon it in succession, as dilute solutions, 3 1/2 parts alum, 1 part chloride of barium, a little free hydrochloric acid, and 1/8 part calcined chalk - stiring well during the operation. The fibres of the paper become firmly coated with the brilliant white sulphate of baryta which is formed. (See also ii. 35.)