84 BULLETIN 343, U. S. DEPARTMENT OF AGRICULTURE. 
(2) The horsepower consumption per ton of pulp when untreated 
wood is ground increases as the pressure decreases according to a 
fairly definite law; it is lower on sharp stones than on dull ones, and 
increases as the speed decreases in much the same manner as it does 
with pressure. There is, however, not as much difference between 
the power consumption per ton at low speed and high speed as there 
is between power consumption at low pressure and: high pressure. 
The power consumption is very little influenced by temperature, but 
it is slightly lower at high temperature. The power consumption is 
higher for seasoned wood than for green wood, and higher for steamed | 
wood than for either seasoned or green material ground under the | 
same conditions. 
(3) The yield of pulp per cord is greater at high pressure than at 
low, and, while this is true also of the screenings, there is not as much 
fine material lost in white water when high pressure is used. The 
yield is not greatly influenced by the surface of the stone, but is 
slightly higher at high speed than at low. The yield is proportional 
to the bone-dry weight per cubic foot of wood. 
(4) The quality of pulp varies greatly with the surface of the stone, 
less with the pressure, and least with the speed. The weight per 
cubic foot and character of wood influence quality to a marked 
extent, especially the latter; temperature also has a marked influence; 
pulp of greater strength is obtained at higher temperature; pulp 
produced at low temperature will take a better finish. Pulp of better 
color can be obtained from green wood than from seasoned, and 
stronger pulp can be obtained by cooking the wood prior to grinding. 
The quality of paper manufactured under exactly the same conditions, 
but made of pulp produced at different grinder pressures, varies 
greatly with the grinder pressure and the horsepower consumption 
per ton of pulp. Mechanical pulp of greatest strength can be pro- 
duced only by the expenditure of a relatively large amount of power. 
PART II.—SUBSTITUTES FOR SPRUCE IN THE MANUFACTURE 
OF GROUND-WOOD PULP. 
EXPERIMENTAL AND COMMERCIAL TESTS ON VARIOUS WOODS. 
Grinding tests of 22 different woods were made at the Wausau 
laboratory. Samples of the experimental pulps were sent to the 
Madison laboratory for tests to determine their quality. The 
experimental apparatus and the methods of operation were the same 
as those used in the case of spruce and described in Forest Service 
Bulletin 127. 
In addition to the experimental tests, ‘‘commercial”’ tests were 
made of the production of pulp and of the manufacture of paper. The 
methods employed in the preparation of the wood and the production 
of pulp were identical with those in the qualitative and quantitative 
