A flax tow sample from China (cf. Table 1) was cooked with oxygen and alkali under various conditions. Yields and properties of the oxygen-alkali flax pulp (OAP) were compared with those of soda (AP) and neutral sulfite semichemical flax pulps (NSSCP).
Alkali charge, liquor ratio, cooking temperature, and cooking time showed significant effects on the properties of pulps obtained (cf. Fig. 1 and 2).
As to the yield and brightness of OAP, the optimum conditions without addition of MgCO₃ seemed to be as follows : 5% alkali charge on sample, 1 : 2 liquor ratio, 11O°C cooking temprature, 3 hrs. cooking time, and 7 kg/cm₂ O₂ pressure, respectively.
It was found that the addition of MgCO₃ was ineffective at lower alkali charge of 5%, but it resulted in remarkable improvement in yield, brightness, and strengths of the pulp at higher alkali charge above 5%, with selective delignification from fiber surfaces and without degradation of carbohydrate (cf. Fig. 3-6).
When compared with the pulps treated by centri-cleaner, OAP was white in color and of much higher brightness than NSSCP, and it required more bleaching chemicals to obtain the same brightness (Table 2).
Paper strengths of OAP (ex. OAP-3, 4) were compared with those of NSSCP. One of the disadvantages of OAP was lower opacity due to the increase of hemicellulose content and bonding area (Table 3 and Fig. 6).
It was shown that OAP was inferior to NSSCP from the color revertion test (cf. Fig. 7).
The color and COD of spent liquor from OAP were less than those of AP and NSSCP (cf. Fig. 8 and 9).

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A fiber classification test of eucalyptus pulp using mesh-graded sieves indicated that the eucalyptus vessel elements were mostly distributed in the fractions between 28- and 42 meshes, and that hardly any of them were found in the fractions coarser than 24-mesh or finer than 80-mesh.
Based on this result, a new method of isolating vessel elements from the pulp was deviced, which provieded eucalyptus vessel elemens almost free of any other pulp components except for trace of wood fibers in an amount sufficients for further studies. The method consists of (1) removing parenchyma cells and fine-sized portion of wood fibers from original pulp with a 80-mesh wire screen, (2) removing the long-sized portion of wood fibers by screening through a 30-mesh wire-covered rotating drum, (3) collecting the fractions rich in vessel elements by riffling, (4) separating the vessel elements from thus vessel-rich portion by gently shaking the dilute suspension in a calture dish, and finally (5) purifying the vessels by decantation in a tall beaker to remove the still remaining short fibers.
It was observed on the sample of eucalyptus vessel elemens that their average dimentions (length : width=0.48 mm : 0.28 mm) were not significantly different from those of domestic hardwoods.
The tylose spheres found in many of the eucalyptus vessel elements were mostly large in size than those in domestic hardwood vessel elements. The inside surface of the eucalyptus vessel wall was carefully exposed and examined by a scanning electron microscope. Notable network structures or crevice structures were observed in some parts of the inside surface, though it has not been concluded if these features are peculiar to the vessels of eucalyptus woods.

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