The influence of various factors such as height, the cut-over area, moisture content, the day elapsed after the felling, heartwood and sapwood on the pH value of wood was investigated. The pH measurement of wood was carried out mainly on the filtrate by a pH meter with glass and calomel electrodes.
The experimental results are as follows :
(1) In the softwood, there was no relation between the pH value of wood and height. The pH value was distributed over the range of pH 6.12 ± 0.016 for SUGI (sapwood) and pH 5.95 ± 0.025 for HINOKI (sapwood). (Table 1)
(2) The pH value of wood was affected considerably by moisture content. Especially, when the moisture content was low (under the air-dried condition), the pH value of wood showed remarkable change with the slight change of moisture content. (Fig. 1)
(3) The pH value of wood was lower as the day elapsed after felling was longer. However, it tended to a definite value as the content of moisture in wood approached equilibrium with that in air. (Fig. 2)
(4) The pH value of wood changed clearly with the cut-over area. The pH values of SUGI, AKAMATSU, HINOKI and BUNA deviated in the range from ±0.1 to ±0.45 with the cut-over area. (Table 2)
(5) The pH value of wood decreased with the increase of temperature of the suspension in water. (Table 3)
(6) There was no relation between the pH value of wood and the lapse of time as the suspension in water. (Table 4)
(7) There was no regularity between the pH values of heartwood and sapwood of all wood. But, in the same wood there was generally regularity between them. For example, in SUGI, AKAMATSU, KABA and NIRE, the pH value of heartwood was higher than sapwood. And in HINOKI, BUNA, KATSURA and SHlNA, its reverse phenomenon was the case. (Tables 2 and 5)