The two sprigns called "Tanaka-no-Yu" and "Hisui-no-Yu" at Misasa Hot Springs, japan (Fig. 1), suitable for sampling the unpolluted water, the locations of which, are shown in Fig. 2, were chosen for this study. The o-phenanthroline method, details of which were discussed in the previous report by the author (Repts. Balneol. Lab. Okyama Univ., 17, 1, (1956)) was used for the determination of ferrous iron, ferrous iron + reducible iron, and ferrous iron + reducible iron + colloidally dispersed iron (to be referred to as "total irons" in this report). For comparison, the change in concentratin of iron dissolved in distilled water during preservation in a sealed bottle was observed, and the results obtained for the solutions with the pH values of 5.4 and 5.8 are illustrated in Fig.3 and Fig.5, rspectively. Both ferrous and reducible iron disappear within 5 minutes, when the pH of the solution is 6.4. The hydrogen ion concentration was thus seen to give a sensitive effects on the speed of diminution of ferrous and reducible iron dissolved in the distilled water. It should be noticed that no appreciable diminution was observed during the period from 60 min. to 120 min,. It is probable that the diminution of total iron is caused by the adsorption of colloidal iron hydroxides on the wall of glass bottle. The effects of charged anion (SO(4)(--)) on the change in concentration of iron during preservation was also investigated, but no appreciable effect was found. (Fig. 5 and Fig. 6). Fig.7, Fig.8, and Fig.9 show the change in concentration of iron during preservation of the spring water at "Tanaka-no-Yu". The content of iron in the spring water is about 0.3 mg/l, and its pH value is about 7.1. For the first 30
minutes, ferrous iron diminishes rapidly, the slope of the diminution curve being sharp and almost straight. Thereafter the slope becomes gentler, and, after an hour, the slope approaches nearly zero. On the other hand, ferrous iron dissolved in distilled water disappears in a moment at the same pH 7.1. Fig.10, Fig.11, and Fig.12 show the change in concentration of iron during preservation of the spring water at "Hisui-no-Yu". The content of iron in the spring water is about 1.0 mg/l, and its pH value is about 6.4. In this case, the diminution of ferrous iron is not remarkable, and only 20% of the initial quantity diminishes within 2 days. Whereas, in the case of distilled water, the diminution is
very rapid at the same pH 6,4, and the ferrous iron disappears completely within 5 minutes. In Fig.13 the speed of diminution of iron in distilled water and that in spring water are compared. The difference here seen may probably be due either to that the ferrous iron in spring water is in a certain complex form not easily oxidizable, or to that the spring water contains some reducing substances.