GROUND-WOOD PULP. 65 
are driven by turbines and motors of less than 300 horsepower 
capacity and 8 per cent of the grinders are driven by less than 200 
horsepower. The work which has been described in this publica- 
tion indicates that a large amount of power to the grinder is desir- 
able. In order to utilize a large amount of power, the stones must 
be operated under conditions of high speed and high pressure, or 
they must be of a larger size than those used at the present time. 
Efficiency of grinding wood can be greatly increased over present 
average commercial practice by the use of higher pressure, since 
this results in the reduction of the horsepower consumption per ton 
of product. There are cases, of course, where such practice would 
not be desirable. If sulphite is available at low cost and power is 
expensive, this condition would surely obtam; but if sulphite is 
expensive and power can be secured at a low figure it is undoubtedly 
more economical to use a large amount of power per ton of product 
and make economies in sulphite by virtue of the fact that with the 
large amount of power better and stronger ground-wood fiber can 
be obtained. 
Economies in grinding, particularly as related to power, depend 
largely on the character of the material into which the ground wood 
is to be incorporated. For the manufacturing of such materials as 
wood-pulp board, as used in the wall-board industry, a long, coarse 
fiber is required, and this is most desirable, since fibers of this nature 
do not form as dense asheet. There are, as a result, a large number 
of air spaces present which retard the passage of cold and sound. 
For the production of pulp of this nature pulp stones of coarse grit 
are required which are softer than those usually employed for the 
manufacturing of pulps for other purposes. When using a coarse 
stone, a longer fiber can be obtained at higher pressure than when a 
finer stone is utilized. Consequently, it is desirable im the produc- 
tion of this character of stock to choose the pulp stone carefully to 
secure the best results. The matter of efficiency as applied to the 
manufacturing of stock for any desired purpoge hinges, to a large 
measure, on a careful selection of the pulp stone to be used. 
It is common practice in ground-wood mills to use all of the pock- 
ets on the grinder in the production of the mechanical pulp. In 
other words, the total amount of power available for use on the 
grinder is used on all of the pockets and at the same time. Power 
can be saved and the efficiency of production increased to a marked 
extent by the utilization of a fewer than the total number of pockets 
of the grinder. If four-pocket grinders are used, it is more desirable 
to use three of the pockets continuously and keep the fourth for 
surplus to be employed at times when one of the other pockets is 
beimg filled or when binding or other troubles are being corrected. 
When all of the power available on a three-pocket grinder is used 
14852°—Bull. 3483—16——_5 
