Square slices of sweet potatoes and potatoes were dried in hot air current at temperatures between 40°C and 90°C, and then their drying mechanism and the optimum drying conditions for sweet potatoes were investigated.
From the results shown in Figs. 3, 4 and 5, it may be said that if the air conditions are kept constant and the samples to be dried are uniform in thickness, drying time for reducing their moisture content to 20 per cent is approximately equal, independent of the varieties of samples and of the initial moisture content.
As shown in Figs. 6, 7 b and 8, on which drying rate is plotted vs moisture content, drying usually proceeded in four rate periods, namely, a constant rate period, a first falling rate period, a second falling rate period A, and a second falling rate period B.
The shrinkages in evaporating area of samples during such periods are shown below the abovementioned rate curves. Here, too, is shown that the shrinkage proceeded in four stages, roughly corresponding to the said four rate periods.
In the drying of sweet potatoes, it was observed, as shown in Table 1 and Fig. 9 b, that the shrinkage in evaporating area was great when the temperature was over 80°C, and that drying time for reducing the moisture content to 20 per cent was minimum when it was kept at about 70°C. These experimental results can be ascribed to the fact that starch in samples gelatinzes over 74°C.
From Fig. 10 and Table 2 presenting the effect of humidity, it may be concluded that the wet bulb depression occurring over 25°C has little to do with the shortening of the drying time.
Thus, it may safely be said that the optimum drying conditions for sweet potatoes are from 60°C to 80°C in temperature and from 25°C to 30°C in wet bulb depression.
Furthermore, several results were obtained on the effect of sample thickness, and at the same time the equilibrium moisture content was measured under different drying conditions.

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燃料として都市ガスおよび発生炉ガスを用い,水中燃焼法による水および亜硫酸パルプ廃液の蒸発実験を行った。燃焼器の熱発生率は80×10⁶kcal/m³hr程度まで高めることができ,60-70×10⁶kcal/m³hr程度の熱発生率で蒸発缶の熱効率は80～90%に達した。亜硫酸パルプ廃液は濃度55%まで濃縮することができ,濃度の高いときの濃縮以外は水の場合とほとんど同じ程度の熱効率を得た。また燃料として発生炉ガスを使用した方が都市ガスを使用した場合よりも着火も容易で燃焼状態が安定していることが観察された。

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Water-cooling data obtained by London et al.⁹⁾ with Ovate-type slats (shown in Table 1 and Fig. 1) and by Simpson and Sherwood¹²⁾ with Redwood slats and Masonite sheets (shown in Table 2 and Fig. 2), were analysed by means of the new methods previously proposed by the author, ⁴⁾ according to which the individual coefficients may be determined by reading the air condition curves on a humidity chart. Experimental formulas on individual film coefficients for each packing were derived; eqs. (1) and (6) for Ovate-type slats, eqs. (2), (3), (7) and (8) for Redwood slats; eqs. (4), (5). (9)and (10) for masonite sheets, respectively.
Moreover, taking into consideration the representation of air rates and water rates, and the area of transfer surface, generalized eqs. (23) and (26) were derived, which may be applicable to over the range of the experimental conditions for R-1, R-2, M-1 and M-2 packings. The relations between the over-all coefficients and individual film coefficients are shown by eqs. (28)a and (28)b and the comparison of the observed and calculated over-all coefficients for R-1, R-2, M-1 and M-2 packings is shown in Fig. 10. Fig. 5 and 6 show the comparison of the performances of Ovatetype slats, Redwood slats, masonite sheets and Raschig rings.

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Some tests were made, on the basis of the fundamental concept of comminution formerly proposed by the author, to study the relation between the performance and the essential grinding mechanism of the tumbling mill, and further to make clear why the industrial radial mill shows a lower grindability.
As the result, it has been proved that the "new" concept is satisfactorily applicable to the industrial equipments as follows:
where K and S_∞ can be expressed by the following equations when other factors remain constant:
K=(1-1.1)×10⁴(g/kWH), almost independent of any of mill types, speeds, or diameters.
S_∞=C·f(N_cr)·D^m, where m=φ(N_cr)
for ball mill, m=0.52-0.53 (N_cr=46-74%)
for radial mill, m=0.13-0.20 (_??_)
The above results are significant in that they help to theoretically explain the correlation concerning the cylindrical mill as:
which equations, however, do not apply to the case of the radial type mill, where,
According to .an approximate analysis in which earlier results²⁾ were employed, the milling action in a ball mill seems to be greatly influenced by the impact of falling balls, while in a radial mill, attrition-grinding between balls and the material might be a controlling factor.
The special features of the industrial radial mill are that although the mill requires only half the energy needed by a cylindrical one of the same size, its capacity is so much smaller than that of the latter that it is not recommendable to connect this type of mill to a continuous long tube mill as a fine grinding compartment.

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