10 JACK PINE AND HEMLOCK FOR MECHANICAL PULP. 



METHODS EMPLOYED. 

 QUALITATIVE AND QUANTITATIVE TESTS. 



In order to cover the field in a reasonable length of time, short tests 

 ranging up to two hours in length were run. In these tests no attempt 

 was made to cover every point, the object being to touch only such 

 as were thought to have a marked effect on the quality of the product. 

 The surface of the stone, the pressure on the grinder cylinder, and 

 the peripheral speed of the stone were the variables which received 

 most attention. No especial attention was given to economic con- 

 siderations. 



Tests were made with pressures of from 20 to 75 pounds per square 

 inch on the cylinder, corresponding to from 8.2 to 30.8 pounds per 

 square inch of pocket area. The speed of rotation of the stone was 

 varied from 84 to 225 revolutions per minute, corresponding to a 

 range in peripheral speed of from 1,173 to 3,150 feet per minute. 



In studying the effect of the surface condition of the stone it was 

 necessary to utilize burrs of many different types and designs. 

 These ranged in fineness of cut from 12 to the inch to 3 to the inch. 

 The style of cut differed also, spiral cut, diamond points, and straight 

 cut being employed. The power applied to the grinder ranged from 

 87.3 to 520 horsepower, while the rate of production of bone-dry 

 pulp varied from 1 ton to 7.3 tons in 24 hours. It should be under- 

 stood that neither the two minimum nor the two maximum values 

 were necessarily obtained from the same test. When the power 

 applied to the grinder was 87.3 horsepower, for instance, it does not 

 necessarily follow that the production was 1 ton per day. The horse- 

 power consumption per ton under the given conditions was found to 

 vary from 68.3 to 196 in 24 hours. 



The samples of pulp obtained during the qualitative and quanti- 

 tative tests were examined and commented upon by members of the 

 advisory committee of the American Pulp and Paper Association, and 

 those runs considered most promising were duplicated later in 

 commercial tests. 



COMMERCIAL TESTS. 

 TREATMENT OF THE WOOD BEFORE GRINDING. 



All of the wood used in the tests was cut either in Wisconsin or 

 Michigan and was representative of the species. In some cases the 

 wood was secured directly from the forest, while in others it was 

 shipped to the laboratory from near-by mills. Upon arrival at the 

 laboratory the logs were closely piled on skids. An attempt was made 

 to keep the material green by painting the ends with paraffin, but this 

 proved unsatisfactory, because the paraffin peeled off. The wood 

 tested was taken directly from the piles for all tests up to and includ- 



