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chemicals, under varying conditions of strength of solution, pressure, and 
duration of digestion.® Therefore it is evident that in valuing an un- 
known material for use as paper stock these differences need carefully to 
be considered. 
The second method for the resolution of raw fibers is of comparatively 
recent origin and consists in cooking them under strong pressure with 
sulphurous acid, either free or combined with soda, lime, or magnesia in 
the form of the bisulphites of these bases. The development of this 
process has been slow, owing to the many mechanical difficulties involved, 
the strong chemicals employed attacking and goon rendering the digesters 
worthless. However, within recent years resistant digester hnings have 
been invented and now this process is established as the leading method 
for the preparation of chemical wood-pulp. Comparatively little has 
been done to show its adaptability to materials other than wood, but the 
process has so many features of superiority over the alkaline one that its 
application in the treatment of various other materials will be considered 
in a subsequent paper when work on the value of Philippine woods for 
paper stock will be reviewed.° 
Bleaching of paper pulp—All fibers do not act alike with bleaching 
agents. Jute, for example, does not bleach white by any known method 
which does not also seriously injure the fiber, while other substances 
require varying proportions of bleach liquor and special conditions of 
treatment to secure satisfactory results. Therefore, it is important to 
subject new, raw materials to quantitative bleach operations in order to 
determine the right method of procedure and the amount of bleaching 
powder required. The loading, sizing and coloring of paper are not 
materially affected by the source from which the pulp is derived and 
need only concern us here with respect to the kinds of chemicals in gen- 
eral use for these purposes and the possibilities of obtaining them in the 
local market. The question of chemicals for this and the other steps 
in the process of pulp manufacture is an important one and will thor- 
oughly be discussed in a later number of this journal. 
VEGETABLE FIBERS. 
Botanical classification of fiber-producing plants.—Fiber plants are 
included in two great divisions of the vegetable kingdom—i. e., Dicotyle- 
° Esparto grass is invariably subjected to the alkaline method of treatment, but 
the pressures carried vary from 5 to 50 pounds, the time of digestion from one to 
six and one-half hours and the strength of the caustic liquor from 10 to 20 per 
eent, calculated upon the gross weight of the material. 
*“On account of the considerable proportion of silica present in straw, it has 
generally been assumed that this material would not easily lend itself to treatment 
by the sulphite process. Practical experience has, however, shown that this is 
not the case, and this process has recently been applied to the preparation of 
straw pulp with excellent results.” Griffin & Little: Chem. of Paper Making, 161. 
