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 | 1916 
Kind of wood. 
er Per Per Per 
Cords ent Cords. pone Cords. cont: Cords. earn 
SPIUCO 2 ss s2- sac eacee seen aee 1,131,377 | 65.2 | 1,332,153 | 59.5 | 1,391,047 | 59.2| 1,803,217 | 63.1 
FemIG GK: #2 ee es eee Soe 31.4 574,109 | 25.6 563, 535 | 24.0 647,738 | 22.7 
POplane =.) cece te oe oa 3, 734 43 || = G255 penne 4,101 ae 2,991 sul 
Balsam 237 wee, Peep Nee key. 24,761} 1.4 81,932} 3.7 100,339 | 4.2 213, 569 7.5 
ine 2 Geka aeee Gauls Ree oe 3,484] .2 As 20 Ne eae 4, 28 : D i 
Waites fir te pee 2 Ep eee pepe ae DASE | Sele, 32,498 | 1.4 35, 865 1.3 
Slab wood and other mill 
WASTE... SIREN. MESS sae. Ne. ee eR eee 219,519 | 9.7 254,914 | 10.8 140, 758 4.9 
All other species. .-..-------- 28,172 | 126 1, 285 1 Oijasecoe 3,779 oll 
Eo Gall ee eee ae sad 167304259) |Reaees PPO MY eee a 2,351, 550 | ee ae | 2, 856, 122 | Seen ae 
} 
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 
preliminary 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. Itis 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 SO, 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 SO, 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 
