HYDKAULICS AND ITS APPLICATIONS 



varying from 284,000 to 856,000 Ibs. per square inch under this tempera- 

 tmv variation. As the temperature is further increased the modulus K 

 diminishes to 819,000 Ibs. per square inch at 212 F. Its values, over 

 the range of temperatures experienced in practice, are as follow l : 



The mean value may be taken in round numbers as 300,000 Ibs. per 

 square inch or 43,200,000 Ibs. per square foot. 



The compressibility is so slight that in all practical calculations con- 

 c-t -ruing water at rest or in a state of steady motion it may be assumed to 

 be an incompressible fluid. In certain important phenomena, however, 

 nniably those involving a sudden initiation or stoppage of motion, this 

 compressibility becomes an important, and often the predominating 

 factor, and in the treatment of such cases the above mean value of K will 

 be adopted. 



In such cases it should be noted that it is the ratio of the bulk modulus 

 to the density of a fluid which forms the true criterion of its compressi- 

 bility or elasticity, as it is this ratio which governs the wave propagation 

 on which such phenomena depend. In this respect air is only about 

 eighteen times as compressible as water. 



At ordinary temperatures and pressures, water is capable of dissolving 

 about 2 per cent, of its own volume of air. As the temperature is raised 

 part of this is liberated. The volume in a saturated solution under a 

 pressure of one atmosphere is approximately as follows 2 : 



At a given temperature the volume of gas absorbed is sensibly inde- 

 pendent of the pressure, so that the weight absorbed is proportional to the 

 pressure. Any reduction in pressure tends to liberate part of the air, and 



Landholt arid Bornstein. Grassi, "Annalesde Chimie et Physique," 1851, vol. 31, 

 ]>. 4:57. irivcs results which are in close agreement with these. 



* A. Winkler, "Zeits. f. Phys. Chemic," 1892, vol. 9, p. 171, and Bohn and Bock, " Wied 

 Ann.," 1891, vol. 48, p. 319. 



