JACK PINE AND HEMLOCK FOR MECHANICAL PULP. 13 



given period; or, in other words, the grinding was carried on at the 

 rate of 512 cubic feet of solid wood in 24 hours. 



The amount of wet pulp obtained during the test was 3,795 pounds, 

 and this upon analysis was found to have a moisture content of 60.22 

 per cent. Consequently, 1,507 pounds of bone-dry pulp were 

 obtained during the period of test, corresponding to a production of 



3~4^ X ?000 or 5 ' 3 tons * n 24 nours - T grind the wood and pro- 

 duce this pulp it was necessary to apply to the grinder motor power 

 which averaged 338 kilowatts. This value was obtained by dividing 

 the total number of kilowatt hours used, as given by a watt-hour 

 meter, by the length of the test in hours. Figure 1 shows a section of 

 a wattmeter record obtained during this test, and illustrates how the 

 power used by the grinder varied upon the removal of the load from 

 one of the grinder pockets. The entire recording wattmeter curve 

 was averaged by means of a planimeter, in order to check the value 

 of power consumed as given by the watt-hour meter. 



By using curves which show the losses in the motor it was found 

 that 15.3 kilowatts were required to supply the heat losses in the 

 grinder-motor armature and 7.1 kilowatts to supply the stray power 

 losses, making a total of 22.4 kilowatts lost in converting the power 

 from electrical to mechanical. This amount subtracted from 338 

 kilowatts gives 315.6 kilowatts which were furnished to the grinder 

 pulpstone, and 315.6 divided by 0.746 l gives the value of 422J horse- 

 power applied to the grinder. In order, then, to obtain 5.3 tons of 

 bone-dry pulp in 24 hours it was necessary to apply to the grinder 

 over that period 422 horsepower, or the horsepower consumption 

 per ton was 422 \ divided by 5.3, or 79.7 horsepower per ton in 24 

 hours. 



The yield from 100 cubic feet of solid wood was obtained by dividing 

 the amount of pulp produced during 24 hours, 5.3 tons or 10,600 

 pounds, by the number of hundreds of cubic feet of wood ground in 

 24 hours, viz, 5.12. The result is 2,070 pounds. 



The average temperature of grinding was determined by reading 

 the recording thermometer every five minutes, adding these values, 

 and dividing by the total number of readings. 



COMPARISON OF YIELDS. 



Much importance is attached to the amount of pulp obtained 

 from a cord of wood, because this represents the efficiency of con- 

 version. Commercial practice in the manufacture of spruce ground 

 wood requires a yield of approximately 2,300 pounds per cord of 



1 A horsepower is equivalent to 0. 746 kilowatt. 



