54 



FOREST PRODUCTS 



Coloring. 



The dyeing or coloring of paper pulp is also done during the beating 

 process and requires considerable care and study. As cellulose is exceed- 

 ingly inactive it is usually necessary to use mordants in order to fix the 

 colors. Soluble coal tar dyes are very commonly used, but there are only 

 comparatively few which are suitable for the coloration of paper pulps. 

 Mineral pigments are often used as well to secure certain bright colors. 

 Poorly dyed papers will bleach when moistened or if exposed to light. 

 The coloring of paper pulps is still in the process of development. 



Paper Machine. 



After the beating process, during which the size, filler and dyes are 

 added, a trap door in the bottom of the beater is released and the mixture 



:3 j»". 



Fig. 9. — Fourdrinier wire, the most specialized machine in the manufacture of paper. The 

 stock is deposited on the wire at the left and the water content is drawn off. A rocking 

 motion of the frame causes the pulp to "felt" properly and the fibers to intertwine. 



flows out through a pipe and into a tank called the stuff chest where it is 

 stored until. needed at the paper machine. The paper machine is the 

 most intricate of specialized machines used in the paper mill and is the 

 key to the successful making of paper. It consists of an endless wire 

 screen called the fourdrinier wire which revolves around a series of 

 rollers. On this screen, the pulp pours in a steady even stream and as 



