In order to clarify the influences of sunlight intensity on the yield of vitamin D by sunlight irradiation of provitamin D, an ergosterol solution was irradiated by sunlight under various circumstances and the yield of vitamin D_2 in the solution was determined according to the procedure described in the previous paper^<1)>. The results are summarized in the following : (1) When the ergosterol solution was irradiated by sunlight of fine days at Kobe in different seasons, yearly variation of the yields showed that these in summer were significantly higher than those in winter and that these in spring or autumn were nearly middle between the two classes ; (2) When the ergosterol solution was irradiated by sunlight of different weather's days at a same place in a same month, the yields of fine days were significantly higher than those of cloudy, smogy and rainy days ; (3) When the ergosterol soltuion was irradiated by sunlight of nearly same weather's days at different places in a same month, there were no significant difference each other except the cases of Shiga heights and Kobe in summer ; (4) There were significant correlations between the yields and the sunlight intensities of both 300〜400 and 300〜330nm ranges, and the correlation with these in the latter's range was higher than those in the former's ; (5) There was no significant correlatation between the yields estimated on fine days and the sulfur dioxide concentrations in atmosphere.

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It was reported in the previous paper^<2)> that there were significant correlations between the yield of vitamin D_2 in sunlight irradiated ergosterol solutions and the sunlight intensities of both 300〜400 and 300〜330nm ranges. This resultsuggests that the yield can be easily calculated by a simple estimation of sunlight intensity in the indicated range. Therefore, the authors estimated the yearly variation of the sunlight intensity at Kobe and the results are summarized in the following : (1) There was a highly significant correlation between the intensities of 300〜400 and 300〜330nm ranges ; (2) The figures of daily variations of the intensities on fine days showed mountain shapes with a maximum at noon in all seasons, whereas those of bad weather's days showed flat shapes in all seasons because sunlight was cut by cloud ; (3) The intensities of fine days from April to September were significantly higher than those from Nobember to January, whereas these of bad weather's days were extremely lower than those of fine days and there were no significantly differences among months ; (4) The yearly variation from Junein 1973 to May in 1975 was estimated as an average per hour of each month. The result showed that the maximum was the value of either July or August while the minimum was that of December and that the former was about twice as high as the latter.

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Hydrolysis of α^4,α^5-O-isopropylidene pyridoxine (4,5-IPP) and factors influencing on the hydrolysis were studied. Solubility of 4,5-IPP in water was better than that of α^4,3-O-isopropylidene pyridoxine (3,4-IPP) but vice versa in organic solvents. In buffer solutions of a constant pH between 1 and 6,the hydrolysis of 4,5-IPP obeyed an apparent first-order kinetics and was faster than that of 3,4-IPP. It was found that ionic strength, buffer concentration and buffer constituents did not influence the hydrolysis rate but concentration of ethanol affected on the hydrolysis. Under these conditions, rearrangement from 4,5-IPP to 3,4-IPP did not occur.

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Solubility and hydrolysis of pyridoxine monooctanoates (PIN-MO) were studied. PIN-4MO was more soluble in organic solvents and water than PIN-5MO. In buffer solutions of a constant pH between 2 and 3,hydrolysis of PIN-MO obeyed an apparent first-order kinetics. The substance passing through the rat intestine was found to be PIN alone.

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