Subject index surface water

Sa.tura.tion Index. Materials of constmction used in pools are subject to the corrosive effects of water, eg, iron and copper equipment can corrode whereas concrete and plaster can undergo dissolution, ie, etching. The corrosion rate of metallic surfaces has been shown to be a function of the concentrations of Cl ,, dissolved O2, alkalinity, and Ca hardness as well as buffer intensity, time, and the calcium carbonate saturation index (35). 

Once initiated, and provided the surface continues to be exposed to the environment, the process of hydration continues at a slow, but measurable rate. The adsorption of the water is accompanied by changes in the physical properties of the obsidian. The refractive index of the obsidian, for example, is altered as it becomes hydrated. If the obsidian was subjected to alternative wet and dry periods, successive hydrated layers are formed on the surface. The differences in refractive index between the bulk and the hydrated layer (or layers) creates an interface between the bulk and the hydrated layer, and between the layers, that stands out sharply when observing a cross-cut section of obsidian under a microscope (see Fig. 23). Thus the thickness of the hydrated layer, or layers, can be measured. 

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