WATER- POWEB. 34T WATER PURIFICATION. ■where the power is rc([uired to obtain the de- sired fall. Occasionally water power ia avail- able in the form of a natural waterfall, and then it is simply necessary to guide the water in a tube or channel to the motor. .Sometimes the velocity only of the llowinf,' stream is employed for working the motor, the head in that ease be- ing already converted into kinetic energy. The preceding table gives the water powers ■which luive notably enhanced tlie industrial de- velopment of the country. In this table the hiatus from 18l!l to ISCG 13 accounted for by the stagnation of industrial en- terprise due to the Civil War. In recent years the possibility of transforming water power into electrical energy and its transmission to dis- tant points has aided greatly in promoting the development of water-power enterprises of great magnitude. The Great Falls, the Sault 8te. Marie, the Niagara, the Ogden, and the Mechanics- ville developments are notable examples of such ■water-power electric jdants. In I'aeh of these cases the water power o]ierates turbines or water wheels which drive dynamos. BiBi.iooBAPiiY. A number of authoritative treatises on water-power development are avail- able. Frizell, Wafer Power (New York, 1901), is a comprehensive general treatise on all phases of the subject. Bodmer, Hydrnulic Motors, Tur- bines, and Pressure Evi/ines (New York, 1889), is an elaborate technical and descriptive treatise on water motors of all kinds. Jlerriman. freat- ise on ffi/druiiHrs (New York. 1900), is a gen- eral treatise on hydraulics, including water motors of various kinds. Descriptions of plants will be found in the volumes of Eiiffineerinp ?^ews (New York, current ) . See Dtn.imo-Electric Ma- chinery; Turbine; Water- Wheel; Hydraulic Engine. WATER-PROOFING. The coating of arti- cles made of textile faln^ics, paper, and other sub- stances, so as to render them impervious to water. Besides the treatment of fabrics with a solution of rubber, various preparations are used, such as a mixture of beeswax and yellow- rosin in boiled oil. Fabrics may also be rendered water- proof by thoroughly impregnating them with a solution of soap and then dipping them into a solution of alum. Paraffin finds extensive use for the purpose, and articles of various kinds, including leather, and even Wood, are made ■^vater- proof by keeping them for a time in hot molten paraflin. Several varnishes, too, are used for rendering articles water-proof. WATER PURIFICATION. The art of re- moving any objectionable matter from water so as to render it safe for domestic consumption and fit for industrial uses. The objectionable quali- ties are in the nature of pathogenic bacteria ; in- ert organic matter liable to give rise to offense or injury; turbidity and suspended matters gen- erally; color, taste., and odor; hardness and iron. (See Water-Works, paragraph on Qtinlity.) The principal means of purification are sedimen- tation, which clarifies water and removes a por- tion of the bacteria ; coagulation, an aid to both sedimentation and filtration; aeration, which re- moves odor and may supplement filtration : filtra- tion, which removes bacteria and reduces inert organic matter, turbidity, and color; and various Vol. XX.— 23. chemical processes for getting rid of citlier iron or hardness. Seuimentation is eilected by either bringing water to rest or passing it very slowly through shallow reservoirs or basins. The first is called the intermittent and the second the continuous system of .sedimentation. The force of gravity carries down some of the clay and sill which comi)o.se turbidity. The degree of clarification elVected depends upon the size and specific gravity of the particles and the length of time afforded for sedimentation. Some waters are notablj' im- proved in a few hours; others are still turbid after a number of days. Partly through the action of gravity, and partly through entangle- ment with the other suspended matter, a consid- erable percentage of bacterial reduction is ef- fected by sedimentation. Where bacterial puri- fication, ratlier than clarification, is the object, sedimentation alone is insufficient, but it may be a great aid to filtration. Storage reservoirs af- ford more or less sedimentation and bacterial reduction, depending upon both their size as com- pared with the daily draught and the character of the water. The design and conslriclion of set- tling reservoirs does not differ from that of other reservoirs, except in the relative shallow- ness of the former., the arrangement of the inlets and outlets, and the provisions 7nade for re- moving the deposits of nuid from their bottom. In continuous-fiow basins having a number of compartments the wat<'r generally pas.ses from one secti<m to another in a thin sheet over a long weir. This insures the drawing off of the upper and clearest layer, minimizes the disturbance of water in the successive basins, and ma}' provide aeration of value. If aeration is dosired and the levels permit it there may be a series of steps between each weir and the next basin. Two or more compartments are usually necessary, so one may be at rest while the other is being filled; but where the constant-flow system is used for water containing but little sediment one basin may do. Provision must be made for drawing the water down as quietly as possible to a level well above the deposit of sediment, so as to avoid disturbing the latter. The bottoms of settling reservoirs should slope to some common point, where connection should be made with a pipe for flushing out the mud when the reservoir is cleaned. The mud is often loosened by means of water under pressure, thrown from a hose, much as in hvdraulic mining. Coagulation is effected by introducing a chem- ical, generally sulphate of alumina, into water. The substance is broken up into alumina and sulphuric acid. The latter unites with the lime or magnesia in the water and is thereby rendered harmless. The alumina thus set free is trans- formed into hydrate of alumina, a white, flaky, gelatinous substance, which coagulates the or- ganic matter in the water and entangles the bac- teria. The agent and the impurities are de- posited in the settling basin or are removed from the water by filtration. It is essential that the water be sufficiently alkaline to decompose the sulphate of alumina, and that plenty of time be allowed for coagulation. If deficiencies in alkalinity are periodic, as in times of heavy floods, they may be made good by adding lime to the water., The time element is secured by pro- viding basins or reservoirs of proper capacity.
