PALITZSCH氏緩衝液及びフェノールフタレイン使用に依る海水pHのー比色測定法
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The author studied the relation between colour ratio, α of phenolphthalein, and its corresponding pH-value of the sea water as determined by BRANDES(1) with PALITZSCHs buffer solution (boric acid-borax mixtures), and found that pH of it is a logarithmic function of α within a range 8.08-8.60 but not a linear one as obtained by BRANDES. My observations as given in Table 1 and Fig. 1 clearly show that a linear relation exists between logα and pH. Thus a colour ratio of pH 8.51 to pH 8.41, for instance, is tabulated to be 1:0.706, so that pH between these two values can be calculated from an equation, α=(0.706)1-x, where x denotes pH values to be added to the 1st decimal of pH 8.41. By such calculation figures denoting the relation between colour ratios and pH were obtained as listed in Table 2. The accuracy of this calculation method was tested by determining pH of PALITZSCHs buffer solutions containing a certain amount of borax solution, (1) by the interpolation of the percentage of borax solution, …… pH1 (2) by the calculation from their α-values according to Table 2, ……pH2 and (3) by the interpolation of α-values assuming pH as a linear function of α1……pH3 (Table 3), It is clearly seen in Table 3 that pH2 is more accurate than pH3. Colorimetric determinations were also carried out in order to obtain α-values of PALITZSCHS buffer solutions containing the indicator, both at the higher and the lower temperature than 18°C. with the results given in Table 4, from which the temperature coefficient of phenolphthalein δ=0.012, (with deviation±0.001) was obtained. This value thoroughly corresponds to the rate of displacement of the halftransformation-point of the indicator due to temperature change as given by MICHAELIS(3). Therefore, the value, δ=0.010, obtained by BUCH(4) seems to me to be too small.