JACK PTNE AND HEMLOCK FOR MECHANICAL PULP. 

 TABLE 1. Average yields from spruce, hemlock, and jack pine. 



15 



One hundred cubic feet of solid wood was selected as the basis of 

 yield, since it eliminates the variable loss in barking, and represents 

 fairly well the amount of solid wood in a rossed cord. The yield, as 

 will be seen, is directly proportional to the bone-dry weight of the 

 wood. The loss in conversion has been found to range between 12 

 and 15 per cent of the original weight of the bone-dry wood. Ap- 

 proximately 6 per cent can be accounted for in the white water and 1 

 per cent in screenings. The manner in which the remaining losses 

 occur has not been determined, but will be studied in future tests. 



The storage capacity for white water in the laboratory was very 

 limited, and this may to some extent account for the low yields. 

 The continuous use of the white water and the use of save-alls would 

 undoubtedly tend to increase the yields and result in saving a great 

 deal of fine pulp. 



The loss in barking j ack pine and hemlock, so far as has been 

 determined up to the present time, is practically the same as the loss 

 in the barking of spruce. There are a great many knots in both 

 hemlock and jack pine, and it is possible that this may cause a some- 

 what greater loss in barking these species. However, on account of 

 the small amounts of the various woods used, no reliable data on loss 

 were obtained. 



FACTORS WHICH INFLUENCE QUALITY AND PRODUCTION. 

 SPEED AND PRESSURE. 



The effect of speed on the quality of pulp can best be illustrated 

 by the magnified fibers shown in Plates VII and VIII. In grinding 

 these pulps the pressure and surface of the stone were maintained 

 constant, and the speeds were, respectively, 100, 150, and 200 revolu- 

 tions per minute for the hemlock, and 152 and 205 revolutions for 

 the jack pine. There is little difference in the fibers ground under 

 these different conditions of speed; especially those run at 150 and 

 200 revolutions per minute. Speed probably has very little effect 

 on the quality of pulp. With satisfactory pressure and curface of 

 stone, it is possible to obtain good grades of pulp at any speeds within 

 reasonable limits. Commercially, it is practically impossible to main- 



