The present paper is concerned with a series of laboratory scale trials on recycling for reuse of waste liquor and washings in the bleaching of birch kraft pulp. The pulp was bleached in a sequence of oxygen-alkali, peracetic acid, and hydrogen peroxide (O-PA-P), and washed countercurrently as shown in Fig. 1.
Pulp brightness could be maintained at 90 without any effluent during at least 10 recycles, if the pH of O-and P-bleaching liquor were kept optimum by addition of NaOH. The amount of fresh water used in this case was roughly estimated at 5 m³ per ton of pulp, but this system required 1.5% (on o. d. pulp) of additional NaOH at O-stage. The additional NaOH could be omitted by increasing in the amount of fresh washing water to 10 m3 per ton of pulp, which may, in turn, increase the load of evaporator.
As compared with conventional sequence (O-D-E-D), in respect of pollutant loads, countercurrent washing reduced total colour and total COD into 1/9-1/10 and 1/8-1/9, respectively, after 10 recycles.

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In this paper, several families of mangrove woods were examined with respect to qualification for dissolving pulps. The results obtained were as follows.
(1) The mangrove wood of the family Rhizophoraceae showed better properties cited below than Japanese hardwoods. The woods of Rhizophoraceae had higher specific gravity and were easier in cooking and bleaching. Most genera of the family contained a large amount of EDTA ash, which was normalized with the elimination method as described in the second and the third reports of this series. In the other properties of pulps, the woods of Rhizophoraceae were more excellent than Japanese hardwoods. In industrial viscose process, the compressibility of sodium cellulose and the filterability of viscose from Rhizophoraceae pulps were more excellent than those from LDP. Two species of the genus Bruguiera of Rhizophoraceae, B. parvifora and B. sexangula, had low content of EDTA ash and suitable reactivity. Two families of Combretaceae and Sonneratiaceae were adequate to dissolving pulps, having the same properties of pulps as those of LDP. The mangrove woods of other families surveyed in this paper were inadequate to dissolving pulps owing to some defects in pulping, pulp quality or reactivity. Among the families of mangrove, the family Rhizophoraceae has the widest distribution in Southeast Asia, and the genus Rhizophora (Bakau and Bakauan) is abundant in the same family. Therefore, the mangrove of Rhizophoraceae is most promissing as a resource for dissolving pulp woods.
(2) Microscopical observation of the woods of Rhizophora (Bakauan) and Bruguira (Langgadai) showed the features such as longer fibers, thicker cell walls, and smaller lumens than those of Japanese hardwoods. The ray parenchyma cells of Rhizophora wood contained a large amount of Ca-oxalate crystals.
(3) In chemical components of Rhizophora wood, the contents of lignin, pentosan, resin and water soluble matters were all lower than those of Japanese hardwood except the content of EDTA ash.

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In previous paper, the correlation between base paper structure and penetration off coatings was studied by observing fiber interfaces of coated layers using the scanning electron microscope.
In this paper, the profiles of coatings penetrated into base paper were obtained by stereo-microphotogrametry on the fiber interfaces of coated layers.
The hand-coated papers were prepared from the two different types of base paper A and B Tow-sideness of base paper A was less, but that of B remarkable.
Results have been summarized as follows ;
(1) When smooth surface as top side of A and B as well as wire side of A was coated, coatings penetrated into the sheet 2030, μ deep from the surface.
(2) When rough surface as wire side of B was coated, coatings penetrated into the sheet 45 μ deep from the surface.
(3) These profiles of coatings penetration were consistent with the results of cross sectional observation by the scanning electron microscope.

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