ETHYL ALCOHOL FROM WOOD WASTE. 65 
DIGESTERS. 
The digesters should be of the rotating kind, and may be spherical 
or in the form of a short cylindrical section with dished ends. If 
they are of the latter type, the diameter should be double the length 
of the cylindrical section in order that the digester may be filled as 
nearly full as possible. A number of satisfactory acid-proof linings 
are now obtainable. During the cooking the mass shrinks in volume 
and settles, the final volume being only about two-thirds the original 
volume. There is, therefore, ample room for thorough mixing during 
the cooking. 
The size of the digesters will be governed by the daily capacity of 
the plant, the heating period, and the time of the complete cycle for 
each digester. If the heating period is 15 minutes out of a total of 
1 hour for each cook, four digesters or multiples of four should be 
used; whereas if the heating period is 20 minutes out of a total of 1 
hour, only three or multiples of three should be used. In this way 
the steam load on the boilers will be made as uniform as possible. 
The boiler capacity will be largely determined by this load, since 
that for power and distillation purposes will usually be constant. 
In addition, the hogging, shredding, and digester capacity of the 
plant should be sufficient to give enough digested sawdust in 18 or 20 
hours to run the rest of the plant 24 hours, thereby allowing time 
for breakdowns and repairs. 
By the rotation of the digester the cooked sawdust is discharged and 
falls into a large bin, which receives this material from all the diges- 
ters. From this bin it goes by mechanical conveyor to the different 
cells of the diffusion battery. 
DIFFUSION BATTERY. 
Closed cells similar to those used for the extraction of sugar beets 
or dyewood chips may be used. These should be lined and made 
acid-resistant like the digesters, and are usually fitted with bronze 
and copper. The top and bottom should be so arranged that charg- 
ing and discharging may be readily accomplished. Cells of this type 
may be obtained from which the extracted material will empty itself 
when the bottom of the cell is released. 
The temperature of the extracting water will rise 30° to 50° F. 
during extraction because of the hot dust. In cold weather it would 
be advisable to warm the water before it is used. If the acid juice 
comes from the battery with a temperature between 125° and 150° 
F., a good extraction will be obtained, and the large volumes of water 
that would be required to cool hotter juice will not be necessary. 
The size and number of cells in the battery and the amount of 
water in each cell will be governed by the size of the plant and the 
54976°— 22— Bull. 983 5 
