The results of this study on the role of neutral resin components on pitch deposition provide the broadest base so far available for relating variation in pulping stages to variation in tendency of pitch accumulation. It is of interest to note that dominant presence of neutral components in lauan resin is the primary cause of the so-called pitch problems associated with pulp manufacturing from lauan waste wood. There are limits within which there would be varying degrees of polarity of the neutral fractions with their pitch-causing potential, and beyond which the polarity of one or other of the neutral fractions does not cause severe pitch trouble. Fvaulation of the components of the neutral fraction of Lauan resin indicates that saturated higher hydrocarbons, saturated aliphatic alcohols, β-sitostero, Ψ-taraxasterone and Ψ-taraxasterol are main constitutents of the pitch trouble causing fractions. The significance of these result is discussed.

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The purpose of this study was to elucidate the effects of cooking and preparative conditions on the color of thiolignin. The experiments were performed by the use of orthogonal array L₂₇ (3¹³). The following factors and levels of experiments were selected :
(A) Sulfidty (% as Na₂O), 0, 15 and 30%.
(B) Active alkali (g/l as Na₂O), 20, 40 and 60g/l.
(C) Time to maximum temperature, 45, 90 and 120 min.
(D) Maximum temperature, 155, 165 and 175°C.
(E) Retention time at maximum temperature, 0, 60 and 120 min.
(F) Precipitant, H₂SO₄ and HCl; dummy level (H₂SO₄).
(G) Time for coaguration, 0 and 10 min.; dummy level (10 min.).
(H) pH at precipitation, 10, 8 and 3.
(I) Wood species, softwood ; dummy level (hardwood).
Japanese Red pine (Pinus densiflora) and beech (Fagus crenata) shavings were used as softwood and hardwood, respectively. Moreover, softwood was replaced by hardwood for the factor (I), and the influence without the factor of wood species was studied, because the color of thiolignin is markedly by wood species.
The isolated thiolignins were examined by the absorption in visible region. The color of solution, expresed by the XYZ system of C.I.E., was calculated from the transmission spectra on the basis of the thiolignin concentration of 0.8 g/l.
The values obtained here were analyzed statistically. The results are summarized as follows :
(1) Sulfidity and active alkali of cooking liquor do not affect the color of thiolignin.
(2) The color of thiolignin is dependent on maximum temperature and the retention time at maximum temperature. The color of thiolignin becomes darker promptly at maximum temperature over 165°C. This darkening is due to the secondary condensation of lignin, i.e. the increase of molecular weight, during cooking.
(3) The liquor pH at the precipitation stage affects the color thiolignin. Namely the color of thiolignin isolated at pH 10 is darker than at pH 8. There is no change of the color of thiolignin isolated at liquor pH 38. Such a difference of color is caused by the solid properties and the chemical structure of lignin macromolecule.

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It was reported in the previous paper that hemicellulose becomes stabilized and the yield increases when kraft cooking is carried out by adding sodium borohydride as the reducing agent to the cooking liquor. However, as sodium borohydride is rather unstable at elevted temperatures, tests were carried out to find the most effective condition, i.e.
(1) carrying out two-stage cooking by reduction pretreatment, (2) changing the ratio of active alkali of the cooking liquor, (3) lowering the pH of cooking liquor on the halfway or at the end of cooking by addition of sulfuric acid.
As a result, it was found that (1) in case of softwood, two-stage cooking by reduction pretreatment for long time at room temperature is effective, and in this case, reuse of the pretreatment solution is possible and it is economical of the reducing agent, (2) in case of hardwood, while the effect of reduction pretreatment is small, cooking by addition of reducing agent under condition of low active alkali is effective, and especially lowering the pH at the end of cooking to make redeposition of hemicellulose is most effective.

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