34 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 



