4 BULLETIN 620, U. S. DEPARTMENT OF AGRICULTURE. 



Table 2. — Consumption of wood by the sulphite process in the United States — Continued. 





1908 



1910 



1911 



1910 



Kind of wood. 



Cords. 



Per 

 cent. 



Cords. 



Per 



cent. 



Cords. 



Per 

 cent. 



Cords. 



Per 

 cent. 





1,131,377 



544,131 



3,734 



24, 761 



3,484 



65.2 

 31.4 



.2 

 1.4 



.2 



1,332,153 



574, 109 



625 



81,932 



4,720 



27, 797 • 



219,519 

 1,285 



59.5 

 25.6 



3.7 

 .2 



1.2 



9.7 

 .1 



1,391,047 



563, 535 



4,101 



100,339 



4,286 



32,498 



254,914 

 830 



59.2 



24.0 



.2 



4.2 



.2 



1.4 



10.8 



1,803,217 



647, 738 



2,991 



213,569 



8,209 



35, 865 



140, 758 

 3,775 



63.1 





22.7 





.1 





7.5 



Pine 



.3 



White fir 



1.3 



Slab wood and other mill 







4.9 





28, 772 



1.6 



.1 









Total 



1, 736, 259 





2, 242, 140 





2,351,550 



2,856,122 













PRESENT METHODS OF OPERATION. 



At the present time there are used in this country two general 

 methods of cooking sulphite pulp, the short and the long, or so-called 

 Mitcherlich, depending on the product it is desired to obtain. The 

 prehminary preparation of the wood is the same for both of these 

 processes. The wood reaches the mill in the log and is then sawed 

 up, usually into 2-foot bolts. These are barked by machine or drum 

 barkers, care being taken that all portions of the bark are removed, 

 because it discolors the pulp. The wood is next reduced to chips, 

 which are put through screens to remove all above and below a cer- 

 tain size. It is very desirable to have them uniform. They are then 

 conveyed to storage bins above the digesters and used as needed. 



In the short cook the digester is filled with chips and cooking liquor, 

 and by means of live steam which enters at the bottom the pressure 

 in it is brought up to 75 or 80 pounds as quickly as possible. The 

 pressure is then kept at this point and the temperature is gradually 

 raised, so that a temperature of 154'° C. is reached at the end of about 

 7 to 9 hours. While the temperature is being raised, the S0 2 gas 

 which is being driven from the liquor in the digester is constantly 

 relieved and reclaimed by absorption directly in tanks or in towers 

 filled with stone. The pressure in the digester is due partly to the 

 steam present and partly to the gas liberated. As the cook progresses 

 the steam pressure increases, but the gas pressure decreases until at 

 the end of the cook there are only a few pounds of pressure due to 

 the S0 2 gas present. The pressure in the digester is kept the same 

 by means of an automatic arrangement, which lets in more steam 

 when the digester is being relieved and shuts it off again when the 

 relief valve is closed. At the end of 3 or 4 hours the condensation 

 in the digester causes it to fill up with liquor, which is relieved usually 

 through an opening about 3 feet from the top. Toward the end of 

 the cook the liquor in the digester gets darker and darker until it 

 reaches a light coffee color. The end point is determined by the color 



