PHYSICAL PROPERTIES OE WATER 



3 



of a reduction of pressure. The specific gravity at maximum density is 

 unity, and the specific heat varies slightly with temperature, increasing 

 from 1*000 at 32 F. to 1*013 at 212 E. 



The latent heat of fusion of ice at 32 F. is about 142B.T.U., while the 

 latent heat of evaporation at 212 F. is 966'6 B.T.U. 



Weight of Water. Authorities differ as to the precise value of the 

 weight at maximum density, the lowest value given being about 62*379 Ibs. 

 per cubic foot and the highest 62*425 Ibs. The latter value that of 

 Rankine is commonly adopted as being most nearly correct. The 

 following table, calculated from Rankine's formula, gives the weight per 



cubic foot at different temperatures. At 212 F. values by different 

 experimenters vary from 59 '56 Ibs. to 59*84 Ibs. Above this temperature 

 the exact values are not so well known and are unimportant to the 

 engineer. For the purpose of all calculations relating to Hydraulics it is 

 sufficiently accurate to take the weight per cubic foot at 62*4 Ibs., more 

 especially as the water with which the engineer has to deal is never per- 

 fectly pure, but contains more or less of the soluble salts. Unless 

 otherwise stated, the above value will be adopted throughout this 

 treatise! 



The density of sea water varies slightly with the locality, but is about 

 T026 times that of fresh water. Its weight, at the temperatures commonly 

 met with in practice, may be taken as 64*0 Ibs. per cubic foot. 



Compressibility. Water is very slightly compressible, the compressi- 

 bility varying with the temperature and with the amount of air in solution. 

 When pure, the decrease in volume 8 V, due to an increment in pressure 

 6 P, of one atmosphere, decreases from '0000518 to '0000412, as the 

 temperature increases from 32 F. to 140 F. (Grassi). 



This gives values of the bulk modulus K, which equals 



d V 

 V 



