Part III.] Raitt : Bamboo as Material for Paper-pulp. 27 
31. These results may be accepted as evidence that the soda process 
will prove satisfactory when digestion is aided by crushing the material 
and by extraction of the starch. When thus dealt with most of the causes 
of the variation hitherto found disappear, as does also the difficulty of 
the nodes, and all species and ages are brought down to so nearly a com¬ 
mon level that the differences remaining can be dealt with by slight alter¬ 
ations in the digester conditions, amounting to not more than 2 per cent, 
of NaOH, 20 degrees of temperature and one hour in time. The one 
point open to objection is the bleach consumption which is undoubtedly 
high even under the conditions of Table VII, though not so high as to 
condemn the pulp, for its cost in this respect is more than compensated 
for by the cheapness of the raw material. It must also be remembered 
that the standard of colour to which the figures refer is a high one, higher 
than is necessary for most of the uses to which the pulp would be 
put. For common grades of printing paper, a consumption of one-half to 
one-third less would be sufficient. It is not likely that the pulp-maker in 
the tropics will be called upon to bleach his product; the paper-maker 
will prefer to do that himself as his requirements in colour vary with each 
description of paper he makes ; but as the value of unbleached pulp de¬ 
pends largely on its bleaching capacity, the pulp-maker must necessarily 
keep that end in view and aim at producing not merely a well-digested 
clean pulp but one that will bleach easily and well. By the soda process, 
under the conditions specified above, he can do so sufficiently well. 
It now remains to be seen whether he can do it better by the sulphate 
method. 
32. Sulphate liquor contains, as its active constituents, NaOH and 
Sulphate process. Na 2 S ( sodium sulphide), the latter varying in 
amount from one-fifth to one-third of the whole. 
The actual digestion is, as with the soda process, done almost wholly by 
the NaOH, Na 2 S having but slight saponifying effect on lignin. Its 
chief effect is to reduce the colouration products formed to compounds of 
a lighter colour and to hold them more perfectly in solution, so that they 
can be easily washed out without precipitation on the pulp. It therefore 
exercises a strong bleaching effect and the pulp produced is consequently 
lighter in colour and more easily bleached by B. P. It has also a retard¬ 
ing influence upon hydrolysis of fibre by NaOH and thus, to a slight 
extent, increases the yield. As the loss of soda is made up with sulphate 
of soda, which is a cheaper article than carbonate, the cost of chemicals 
is slightly less than for the soda process. The objection to it is the odour 
of sulphuretted hydrogen (the rotten egg smell), given off when discharg- 
[ 207 ] 
