WOOD PULP AND PAPER 37 



moisture possible in order to reduce freight rates. Before hydraulic 

 pressure is exerted, the sheets of pulp generally contain from 50 to 75 

 per cent of moisture. 



Yield. 



The following table shows the amount of pulp made by the mechanical 

 process from a cord of the principal kinds of wood used. 



Species Pulp Produced in Pound 



Spruce 1600-2200 



Poplar. 1400-2000 



White pine 1600-2000 



Aspen 1600-1800 



Cottonwood 1900-2000 



Hemlock. . 800-1100 



Pulp manufacturers generally estimate a yield of about 2000 Ib. of 

 air-dry pulp from spruce. The yield by the mechanical process is much 

 greater than by the chemical processes. 



The variation in weights given is due to variation in moisture content, 

 condition of wood, methods of manufacture, efficiency in recovery of 

 waste or unscreened wood, etc. 



About 85 per cent of all the wood used in the mechanical process is 

 spruce. 



The cost of producing mechanical pulp depends upon a number of 

 conditions such as: 



1. Cost and kind of wood. The cost of wood has been a variable 

 factor, with the tendency in recent years to increase rapidly. (Wood 

 prices have been discussed earlier in this chapter.) 



2. Size and equipment of the plant. 



3. General efficiency of the labor, methods and machinery. 



4. Nature of pulp produced. 



The cost of producing ground wood pulp per ton may be summarized 

 as follows: A variation is given because the cost figures cover a wide 

 latitude depending upon the factors given. It should be understood 

 that these are pre-war estimates. 



Under conditions prevailing before the war, the minimum figure of 

 Si 6. 60 would be about the average cost of producing ground wood pulp, 

 but all materials, especially wood and machinery have increased very 

 materially so that the maximum figures are more nearly a reflection of 

 recent conditions. 



