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Investigation of ORP (Oxidation-Reduction Potential)
Measurement on Sulfur Springs and Its Applicationon Hot Spring Waters in Nozawa Onsen
Takuya MORIMOTO+, Hidekazu KOJIMA+, Shoichi OKOUCHI,
and Hideyuki ONAMI,

Abstract
Although geochemical analysis of hot spring waters is the best way to characterize
the chemical condition of hot springs, it is not suitable for a multipoint investigation ofaged deterioration and route of hot springs from the viewpoint of cost, mobility, andsimplicity. Therefore, an exploration with ORP/pH meter, which is a handy and mobile
device for hot spring research, was carried out in order to measure the e#ectiveness of
ORP measurement.
We studied both acidic sulfur springs containing H,S and alkaline sulfur springs
containing HS in this paper. The ORP/pH meter measurements revealed aging andchanges in water quality of sulfur springs. A practical research was applied for alkaline
sulfur springs in Nozawa Onsen, and found that there are few di#erences between the hotspring waters at the fountainheads and those at the bathtubs. The result conﬁrms that
hot spring waters have been o#ered in good condition to most accommodations in
Nozawa Onsen. Moreover, the application of ORP measurement has pointed out the problems of some accommodations. After the improvement of their bath facilities, the qualityof the hot spring waters in Nozawa Onsen was also improved. The result conﬁrms that
ORP measurement is an e#ective indicator when we observe the condition of hot springs
easily and quickly.
Key words : ORP (Oxidation-Reduction Potential), Aging, Sulfur spring, Nozawa Onsen,
Management of hot springs+ +/*ῌ***,  ,ῌ+3ῌ+/ + Nippon Onsen Research Institute,,ῌ+3ῌ+/ Shibuya Shibuya-ku Tokyo +/*ῌ***,, Japan.
, !"#$!% +2.ῌ2/2. &'()*+, -ῌ1ῌ, , Faculty of Bio Science and Applied Chemistry, Hosei University, -ῌ1ῌ, Kajino-cho Koganei-shi Tokyo +2.ῌ2/2., Japan.

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ORP-pH relationship.
 : Point where spring ﬂows (Upper Yubatake).  : Lower Yutaki (Lower Yubatake).
 : Pouring gate to public bath.
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according to various forms of spring ﬂow.
Borderline of expected change in quality of hot spring water.
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 - ORP-pH 
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 : Hot spring water in bathtub.
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 0 ῌ
 ORP-pH  2  ! "#$% S & '( +* mgῌkg )*$&+ ,- . /&0&1$ /3.3 mgῌkg +330  ' 234&5&1$ /..+ mgῌ
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