12 JACK PINE AND HEMLOCK FOR MECHANICAL PULP. 



LOSSES IN GRINDING. 



To determine approximately the losses occurring in the conversion 

 of wood to pulp, the bone-dry weight of screenings obtained from a 

 known amount of bone-dry wood was determined. The loss in the 

 white water v/as then taken as the difference between the bone-dry 

 weight of the wood ground and the bone-dry weight of the pulp 

 secured plus the screenings. 



FIBER STUDY. 



During each test the character of fiber obtained was examined by 

 means of an apparatus for microscopic study. This consists of an 

 ordinary stereopticon provided with a specially constructed carrier 

 for microscopic slides. Samples of wet pulp were taken from the 

 wet-machine vat and slides were made by first removing the water 

 by drying, then staining with Bismarck brown, and moistening with 

 glycerine. The mixture of glycerine and fiber was teased out to 

 cover the area of an ordinary microscopic cover glass, which was 

 placed over the mixture. Evaporation or leakage was prevented by 

 means of a thin strip of shellac around the edge of the cover glass. 



With this apparatus it was also possible to compare different 

 samples of pulp with the commercial standards used, the latter being 

 selected from a large number of samples submitted by American 

 manufacturers of ground-wood pulp. 



CALCULATION OF RESULTS. 



To give a clear understanding of the method employed in calcu- 

 lating the various items in connection with a test, all the calculations 

 for a representative run, No. 50, Table 4, are given here. Consid- 

 erable data taken during the tests have been eliminated from the 

 compilation, since they have no direct bearing on the study. 



The test mentioned required 3.42 hours to complete, and during 

 that time 3,388 pounds of hemlock wood were ground. For com- 

 parison all of the figures on weight of wood were brought to a 

 bone-dry basis. The bone-dry weight of wood was secured by 

 drying a known volume of wood to constant weight and calculating 

 the weight per cubic foot. By calculating the bone-dry weight of a 

 log of measured volume and subtracting this amount from the actual 

 weight of the log, the moisture content of the wood was determined. 

 The bone-dry weight of this wood, per cubic foot, was 24.84 pounds, 

 and the moisture content was 46.5 per cent; consequently the amount 

 of bone-dry wood ground was 53.5 per cent of 3,388, or 1,810 pounds. 

 This is equivalent to 72.9 cubic feet of solid wood ground during the 



