PRODUCING SODA PULP FEOM ASPEN. 7 
In regard to the time required for cooking there is a wide difference In practice. 
However, the most improved plants are now able to effect the complete resolution of 
the wood in a very short time. In fact, any of the deciduous woods can now be 
reduced in about four hours. With the improvements in the methods of cooking that 
have been developed, which enable us to get about twice the work out of a digester 
that was formerly obtained, a number of special advantages have been found to be the 
result of these quick cooks. The shorter the time the alkali is in contact with the 
cellulose, the higher is the yield obtained and the sounder and stronger is the fiber. 
If all of the cellulose is freed from the lignin at practically the same time, the free 
alkali will have very little time to react on the weaker celluloses and the fibers will not 
be broken nor the points and serrations dissolved. Moreover, the fibers from the short 
cook are not hard to bleach, because the character of the cellulose is uniform. Under 
conditions of complete saturation with the right proportion of alkali, the lignocellu- 
loses can be almost instantly dissolved by subjecting the material to the temperature 
and pressure that is ordinarily used for cooking the fiber. The writer has performed 
this experiment on a laboratory scale, and the fiber obtained so closely resembled the 
actual structure of the woody cell that hardly any cellulose could have been, dis- 
solved. 
Clapperton/ in 1907, in writing about the soda process, says: 
It is the necessity for employing such high temperatures and pressures (90 pounds 
per square inch) that constitutes the serious drawback to the alkali process as under 
the conditions of boiling the strong caustic soda acts on the cellulose, impairing the 
strength and reducing the yield. 2 The reason why such conditions are necessary is 
that the soluble acid bodies resolved by the caustic become so oxidized and con- 
densed that they counteract and weaken the reducing action of the soda, and in order 
to equalize their resistance higher temperatures and pressures have to be employed. 
Beveridge 3 recently published the results of some of his experi- 
ments on the effects of varying the cooking conditions in the produc- 
tion of esparto pulp. He says : 
The treatment of esparto by the soda method is typical of the preparation of paper 
pulp from nearly all fiber-yielding plants, such as bamboo, straw, wood, etc. The 
isolation of cellulose is brought about by digesting the prepared plant in an alkaline 
solution, having for its base caustic soda, at variable temperatures and under variable 
lengths of time. The chemical reaction which takes place during this digesting proc- 
ess is not known; that is to say, has not been isolated because of the complicated char- 
acter of the encrusting substances surrounding the fiber in the plant. The caustic 
soda in aqueous solution forms soluble compounds with these encrusting bodies and 
dissolves any silica which forms a part of the plant's structure, so that by subsequent 
draining, washing, and bleaching the liberated cellulose is obtained in a compara- 
tively pure state. Cellulose from whatever source it is obtained is, however, soluble 
in aqueous solutions of caustic soda. Moreover, the solvent action of the caustic is 
accelerated by heat and by the length of time (within limits) in which the two bodies 
are heated together. It is therefore apparent that if the maximum yield of cellulose 
is desired when using this method due regard must be paid to the laws regulating the 
yield. These laws may be expressed thus: The yield of cellulose obtained from any 
plant by the caustic-soda method depends upon: 
(1) The proportion of caustic soda (NaOH) used per unit weight of plant; 
(2) The temperature employed; and 
(3) The length of time the digesting operation is continued. 
1 Practical Papermaking, p. 33, 2d ed., 1907. 
2 In modern commercial practice even higher temperatures and pressures are employed, and the results 
of the Forest Service tests do not corroborate Clapperton's statements as to the undesirable effects from using 
them. 
3 Papermaker's Pocketbook, p. 72, 2d ed., 1911. See also Sindall, Manufacture of Paper, p. 77, 1908. 
