32 



BULLETIN 343, U. S. DEPARTMENT OP AGRICULTURE. 



remarkably good results, and, being available in large quantities, 

 should serve as a raw material for this purpose. Tests made on 

 sheets composed entirely of boiled and steamed ground-wood pulp 

 show that wrapping papers which will test from 0.50 to 0.75 of a 

 point to the pound are easily produced. Wrapping papers of this 

 kind are inclined to be brittle and do not have sufficient strength in 

 tearing or folding without the addition of a small amount of chemical 

 fiber. 



Resinous woods, if given a mild steaming or boiling treatment prior 

 to grinding, are rendered much more free from pitch, although the 

 pulp is made very soft and darkened to some extent. The use of 

 this method for the production of news print paper would undoubt- 



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 HORSEPOWER PER TON OF PULP [BORE DRY] 



Fig. 22. — Relation of strength of paper per horsepower to power consumption per ton of pulp. 



edly be costly on account of the handling necessary, the cost of steam- 

 ing, and the loss in yield. 



SUMMARY OF INFLUENCE OF GRINDING AND COOKING CONDITIONS IN THE PRODUC- 

 TION OF SPRUCE PULP. 



The experiments conducted by the Forest Service, both in cooking 

 spruce prior to grinding and in varying conditions of producing pulp, 

 have led to the following conclusions: 



COOKED WOOD. 



(1) Cooking spruce prior to grinding results in a stronger fibered 

 pulp, although at least 25 per cent more power per ton is required 

 than is used in grinding untreated wood. The horsepower consump- 

 tion per ton when grinding under conditions of varying cylinder pres- 

 sure decreases to a minimum at approximately 65 pounds pressure 

 on a 14-inch cylinder; this holds for dull or sharp stones. 



