160 



GROUND WOOD PULP MILLS AND CHEMICAL FIBER MILLS 



II. Soda process. This process consists of: — 



(a) Removing barl< in a "barker," consisting of knives 

 spanned into a rapidly rotating disc; 



(b) Grinding and dissecting the bolts into fragments about 

 V24 inch by 1 inch in size ; 



(c) Charging the ground material into annealed and welded 

 steel digesters (of about 15 feet diameter and of 50 feet 

 height) containing a solution of caustic soda; 



(d) Boiling by live steam under a pressure of 125 pounds; 



(e) Blowing the product against a target; 



(f) Repeated washing and screening; 



(g) Bleaching with chlorate of lime; 



(h) Fishing the product thus obtained from a stream of 

 water by endless screens and by endless belts of flannel 

 cloth, in the "fourdrinier," and drying it between heated 

 rollers ; 



(i) Reclaiming caustic soda by boiling in vacuum vats and 

 by melting in the "incinerator." 



Miniature of beater, fourdrinier, and calender made by Heller & Merz Co., 



Newark, N. J. 



Barker for pulpwood. Trevor Mfg. Co., 

 Lockport, N. Y. 



Incinerator used in regaining caustic soda, made by Manitowoc Engineering Works, 



Wisconsin. 



III. Sulphite process. It differs from the soda process notably in the 

 points "c," "d," "e," and "g." 



The wood fiber is first cooked without chemicals and then boiled for 

 60 hours in lead-coated digesters with calcium sulphite, a cheap chemical 

 usually prepared at the mill itself. 



No or only little bleaching is required, the fiber being fairly free from 

 color when leaving the digester. 



Sulphite digester, made by 

 Manitowoc Eng. Works, Wise. 



