The relationship between absorption spectra and sulfur compounds, such as hydrosulfide, polysulfide, and thiosulfate ions, contained in sulfur springs were examined.
(1) The maximum absorption at 230mμ, which is due to hydrosulfide ion, is observed in neutral and weak alkaline sulfur springs. The absorption curve changes its shape markedly on exposure to the air. The change is caused by the oxidation of hydrosulfide ion to polysulfide and thiosulfate ions. The absorption in the region of 220-260mμ, which is due to hydrosulfide ion, decreases with time, but when hydrosulfide ion is oxidized to polysulfide ion, the absorption at wave length longer than 260mμ, which is due to polysulfide ion, increases for a short time and then it decreases.
(2) The absorption of hydrosulfide ion changes with deviation of pH value and the relationship between absorbance,
D, and concentration of hydrogen ion is given by the following equation:
1/
D=1/ε
1⋅
CH
2S+[H
+]/ε
1⋅
CH
2S⋅
KH
2S
where ε
1 is the absorption coefficient of HS
-,
CH
2S is the total concentration of H
2S, and
KH
2S=[H
+][HS
-]/[H
2S]. Plots of the reciprocal of absorbance against concentration of hydrogen ion is experimentally linear under constant total concentration of H
2S. Formal dissociation constant,
KH
2S, is calculated from the equation.
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