GROUND WATER IN NORTH-CENTRAL TENNESSEE
GROUND WATER IN NORTH-CENTRAL TENNESSEE
GROUND WATER IN NORTH-CENTRAL TENNESSEE
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106 <strong>GROUND</strong> <strong>WATER</strong> <strong>IN</strong> <strong>NORTH</strong>-<strong>CENTRAL</strong> <strong>TENNESSEE</strong><br />
takes from the silicate an equivalent amount of sodium. In this way<br />
the filtered water is completely softened, although the total quantity<br />
of dissolved mineral matter is not decreased, and the quantity of<br />
sodium may be so increased as to induce foaming to a troublesome<br />
degree. When all its exchangeable sodium has been replaced the<br />
silicate becomes inert. If, however, a concentrated solution of com<br />
mon salt is passed through the inert silicate, the exchange reaction is<br />
reversed, sodium from the salt displaces the calcium and magnesium,<br />
and the silicate is reactivated. After it has been flushed with soft<br />
water the exchange silicate can again be used as a softening agent.<br />
The exchange silicate process softens water more completely than<br />
the lime and soda process, although it does not reduce the total<br />
quantity of dissolved solids. It is likely to be somewhat more costly<br />
than the lime and soda process if the water to be treated has only<br />
carbonate hardness. On the other hand, it is generally less costly if<br />
the water contains much noncarbonate hardness and if salt for reacti<br />
vating the silicate is not unduly expensive. The principal advantages<br />
of the exchange silicate process are that the water can be completely<br />
softened if desired and that close technical control is not essential.<br />
During recent years this process has been successfully adapted to<br />
treating as much as 5,000,000 gallons of water daily, as at McKees<br />
Rocks, Pa.; it has also been adapted to the needs of the single house<br />
hold in units of small capacity that can be operated with nominal<br />
attention.<br />
Hydrogen sulphide. Hydrogen sulphide (H2S) is a gas that gives the<br />
characteristic odor to sulphur waters, the same odor that is associated<br />
with the decomposition of eggs and other organic substances that<br />
contain considerable sulphur. It is easily detected by its character<br />
istic odor in concentrations as slight as 1 part per million or less,<br />
although it is difficult to determine quantitatively if the concentratio<br />
is much less than 5 parts per million. Hydrogen sulphide is quickly<br />
dissipated or is oxidized to sulphate when a sulphur water is allowed<br />
to stand in contact with air, so that it must be precipitated as an<br />
insoluble sulphide, usually cadmium sulphide, when a sample for<br />
quantitative analysis is taken. It is generally held that hydrogen<br />
sulphide in ground waters of meteoric origin is formed by the reduction<br />
of sulphates, as is brought out by a review of the literature cited by<br />
Renick.69<br />
Hydrogen sulphide, if present in large quantities, imparts to a<br />
water a decidedly disagreeable odor and taste that makes the water<br />
unfit for domestic uses. In the presence of air it combines with the<br />
dissolved iron to form the black ferrous sulphide, which generally<br />
Renick, B.C., Some geochemical relations of ground water and associated natural gas in the Lance<br />
formation, Montana: Jour. Geology, vol. 32, pp. 668-684,1924.