WATER-METER 1095 



Fiihr. is taken as 1000. Water is taken to measure amounts of heat also. The heat 

 required to raise 1 gramme of water 1 Cent, is a unit of heat. The amount of heat 

 required to raise 1 Ib. of water, one degree of Fahr., requires for its evolution the 

 expenditure of a mechanical force equal to the fall of 772 Ibs. through the space of 

 1 foot. Or 1 gramme of water is heated 1 (Cent.) by an amount of heat represented 

 by the fall of 423'55 grammes through the space of 1 meter. The latent heat of 

 water and the amount required to convert ice at the freezing point into water is 144, 

 or 144-6 Fahr. (80-80 1 34 Cent.) The refractive power of water, or its index of refrac- 

 tion of light, is I '336 ; that is, the sine of the angle of incidence is to the sine of the 

 angle of refraction as 1'336 to 1. Refractive power increases below 39', although 

 density diminishes. Water expands when heated or cooled beyond 39 Fahr., or 3 >U 9 

 Centigrade : Playfair and Joule give 39'1 ; Fraukenhein, 38'85 ; Pliicker and Gessler, 

 38'8. Hope, who discovered the property, gave 39'5. Water freezes in crystals ; one 

 form is not unlike Iceland spar, a rhomboid. Hail crystallises in six-sided pyramids, 

 base to base ; snow frequently with various stellar radiations. 



Specific gravity of the vapour of water is 0'622 ; it is nine times heavier than 

 hydrogen. Water itself is 812 times heavier than the atmospheric air. Water ex- 

 pands by heat, between 32 and 212, 1 in 21'3 volumes. Itexpands in cooling below 

 32, even if it be not allowed to crystallise. The expansion may be prevented by 

 using smooth vessels and preventing disturbance. It may be cooled in this way to 

 about 7 Fahr. A. slight agitation, or the presence of a rough substance, rapidly causes 

 it to shoot out crystals in all directions. The spec. gr. of ice is 0'916, it therefore 

 floats on water. It expands with irresistible force, bursting asunder iron vessels, 

 however strong, in which it may be confined, water-pipes of whatever substance, 

 porous stones which may have absorbed it, and vegetable-cells in which it may 

 be enclosed. 



Water heated to 212 Fahr. boils. Long before this period, and even in heating it 

 only a few degrees, it gives off bubbles, which are those of air, from which it is never 

 found free in nature. At 212 the bubbles of vapour are formed and rise to the sur- 

 face. These bubbles form more readily on certain surfaces ; on metals easily, especially 

 if they are not polished. Gay-Lussac gave the difference of the boiling point in metal 

 and glass as two degrees. M. Marcet found it raised to 221 when a glass flask had 

 its inner surface coated with a thin film of shell-lac. When water has ceased to boil 

 in a glass or porcelain vessel, it will begin again instantly if a metallic wire is intro- 

 duced. Eough glass and porcelain vessels allow water to boil better than smooth. 

 The boiling of water depends on the pressure of the air as well as temperature, as the 

 following shows : 



Barometer, inches Water boils at clegs. Fahr. 



2774 208 



28-29 209 



28-84 210 



29-41 211 



29-92 212 



30-6 213 



This change of boiling point is used to ascertain the height of mountains, 550 feet 

 making a difference of 1 degree. In a vacuum water will boil at 67. In a Papin's 

 digester it is raised to 300 or 400 without boiling. 



WATER-GLASS. See GLASS, WATER. 



WATERING- OP STUFFS (Moirage, Fr.) is a process to which silk and other 

 textile fabrics are subjected, for causing them to exhibit a variety of undulated reflec- 

 tions and plays of light. See MOIRE. 



WATER-METER. An apparatus by which the quantity of water supplied to a 

 manufactory or to a house can be satisfactorily measured. As a description of gas- 

 meters has been given, it appears requisite that some notice should be taken of an 

 equally important instrument for measuring water. These may be, and are, variously 

 constructed. The principle upon which they are made is in all cases that which wo 

 see in action in a water-wheel, a given quantity of water in flowing performs a given 

 quantity of work. 



Siemens and Adamson's water-meter is shown in the following figures : 



Fig. 2093 is a plan of a meter, looking on the dial and dial-cap. 



Fig. 2094 is a section of meter, filter, and unions, complete. 



Fig. 2095 is a perspective view of drum or measuring medjum, showing the 

 adjusting or regulating vanes a a a, and water-ways b b b ; letters of reference refer 

 to similar parts in all the drawings. 



lufy. 2094, A is the inlet union of meter for connecting to the Water Company's 

 supply pipe. B is the filter-case, c is a filter, which is for the purpose of preventing 



