The purification of unbleached wood pulp by means of chlorination followed by alkali boiling was studied. The unbleached pulp was chlorinated with chlorine water of various concentrations for one hour, washed and pressed to 70% water content, and then added with NaOH solution of various concentrations in proportion of 4l to 200g pulp, and boiled in an autoclave at 125°C and 2.5 atm. pressure for 4 hours. The results of experiments were as follows :
1) When the purification is carried out with various additions of NaOH, keeping the amount of chlorine used at the same proportion (1.5% of pulp), the α-cellulose content increases, the copper number decreases, and the yield of pulp decreases with an increase in addition of NaOH.
2) When the addition of NaOH is kept at 20% of pulp, the α-cellulose content decreases and the copper number increases, as the amount of chlorine used increases between 1.5 and 5.0%. The α-cellulose content however decreases slightly with a decrease in the concentration of chlorine water which is lower than 1.5%, therefore it gives a maximum point at 1.5%. The yield of pulp is almost the same.

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