66 BULLETIN 348, U. S. DEPARTMENT OF AGRICULTURE. 
on three pockets, due to the need of filling and frequent binding of 
the wood in the cells, the total power is used about 88 per cent of 
the time. In other words, only 88 per cent of the power is being 
used continuously. When two pockets on the same three-pocket 
grinder are used to consume the total power and the third is kept 
for surplus, as previously outlined, all of the power is in use approxi- 
mately 93 to 95 per cent of the time. Here a saving can be made 
and the efficiency increased without the installation or use of any 
additional apparatus, simply by means of increasing the pressure 
on the grinder cylinders, since this would be necessary if all of the 
power were applied to two imstead of the three pockets on that 
piece of apparatus. Of course, this does not have as great bearing 
on the increasing of efficiency when grinders are motor driven; but 
in case of the direct connection to turbines it will be seen that it is 
of great consequence. 
When grinders are motor driven, the most efficient utilization of 
the power can be accomplished by the installation of a grinder-cylinder 
pressure-regulating valve controlled electrically from the bus bars, 
the idea being to increase the pressure when for any reason the power 
consumption falls off. 
Not only does the increasing of pressure on the cylinders result in 
the lowering of the horsepower consumption per ton, but there is at 
higher pressures an increase in the quantity of pulp which can be 
secured from a cord of wood, and this is another vital factor in the 
study of the efficiency of production of mechanical pulp. In any case 
it seems desirable to study carefully the grinding conditions, the speed 
of the pulp stone, the pressure employed, and the character and grit 
of the stone in use, since it is to these factors that practically all losses 
and gains can be traced. The manipulation of the grinder and its 
feeding and operation by the grinderman are also of prime importance, 
since without careful watching the binding of the wood in the pockets 
or some like difficulty may result in reduction of the production from 
the grinder and also in the lowering on quality of the resultant product. 
Even with careful watching there are times while the grinder is appar- 
ently running satisfactorily when hardly three-fourths of the total 
power available for its use is being consumed, due to the binding of 
the wood in the pockets. 
FUTURE SUPPLIES FOR THE GROUND-WOOD INDUSTRY. 
Of the woods tested, Alpine fir, Engelmann spruce, lowland fir, 
lodgepole pine, balsam fir, white fir, amabilis fir, noble fir, Sitka 
spruce, western hemlock, and eastern hemlock all give promise of 
being suitable for the production of news-print papers. Color is here 
the chief consideration. An acceptable news-print paper can not be 
made from such a dark-colored pulp as that of tamarack. Yet this 
does not bar tamarack as a raw material for the ground-wood indus- 
try; it will give a thoroughly satisfactory grade of yellow manila. 
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