GROUND-WOOD PULP. 



13 



In all of the experiments conducted in cooking wood prior to grind- 

 ing, the temperature corresponded to the temperature of boiling at the 

 steam pressure under which the cook was being made. Attempts 

 were made to secure by-products, but the amounts of wood used were 

 so small that this could not be done satisfactorily. 



INFLUENCE OF PRESSURE, TEMPERATURE, AND TIME OF COOKING. 



When the length of time of the cook is kept constant and the cook- 

 ing pressure or temperaturo is varied, it is found that the color of the 

 pulp made darkens greatly when these factors are raised, all other 

 conditions being the same. This is demonstrated by reference to the 



280 



I 2 3 4 5 6 7 8 9 10 tl 12 13 14 15 



HOURS Or STEAMINQ 



Fig. 5. — Effect of duration of steaming on color of pulp. (Average values of several runs on spruce.) 



curves in figures 4 and 5, where the amount of black in the color as 

 determined by a tintphotometer is plotted against the cooking pres- 

 sure and temperature. At some steam pressure the wood will char 

 and the resultant pulp will be black ; under this condition a maximum 

 of 300 parts black would be secured. It is probable that this steam 

 pressure would not be very high, since the values of parts of black 

 increase rapidly after 60 pounds pressure is reached. 



The strength of the pulp increases with the length of the steaming 

 period (fig. 6) and seems to reach a maximum in about 8 hours for 

 both pressures. In figure 7 is shown the variation of the yield of pulp 

 per 100 cubic feet of solid rossed wood, with the pressure of steaming 

 and the duration of the cook. The marked effect of the duration of 

 the cook, especially at high pressure, is evident. The yield decreases 



