. Principles and practice of plumbing . ter, it reacts upon the sulphates of lime and mag-nesia, decomposes them and forms insoluble carbonateswhich are precipitated. The reagents generally used in softening arecaustic lime (common quick lime) and soda ash, Otherreagents can be used, but the above are generally selected Digitized by Microsoft® 228 Principles and Practice of Plumbing on account of their cheapness and because they are readilyobtainable in any market. Water Softening Apparatus.—An apparatus forsoftening water consists of a mixing chamber for the chem-ical reagents, a settl
. Principles and practice of plumbing . ter, it reacts upon the sulphates of lime and mag-nesia, decomposes them and forms insoluble carbonateswhich are precipitated. The reagents generally used in softening arecaustic lime (common quick lime) and soda ash, Otherreagents can be used, but the above are generally selected Digitized by Microsoft® 228 Principles and Practice of Plumbing on account of their cheapness and because they are readilyobtainable in any market. Water Softening Apparatus.—An apparatus forsoftening water consists of a mixing chamber for the chem-ical reagents, a settling basin for the treated water afterthe reagent is added and a filter to remove from the soft-ened water the base acted upon by the chemical. There are two general arrangements of apparatus forsoftening water. One arrangement is known as the closedor pressure system, and the other arrangement, as thegravity system. The general arrangement of the Scaife pressure systemas used for softening feed water for boilers is shown inFig. Fig. 113Ilcssiire Walii- Softeniufc Systiin Feed water enters the open heater, a, where some ofthe temporary hardness is removed by raising the temper-ature to 200 or 210 degrees Fahrenheit, thus driving offsome of the free carbonic acid gas and precipitating car-bonates of lime and magnesia on removable pans inside ofthe heater. From the heater the water is forced by theboiler feed pump, b, into a large precipitating tank, c, wherethe chemical reagents are introduced by means of two smallpumps, d, d. In the precipitating tank most of the remain-ing carbonates and sulphates of lime and magnesia are pre-cipitated; some of the lighter particles, however, are carried Digitized by Microsoft® Principles and Practice of Plumbing 229 in suspension to the filters, e, e, where along with other im-purities they are removed. When this system is used for industrial or for domesticpurposes, the heater and feed water pumps may be omittedand the hard water di
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