12 



Figure 11 - Cavitation Erosion on Concrete Specimens— Prom 

 Bureau of Reclamation Photographs 



and to explain the wide discrepancies between theoretical and observed results, 

 the question of cavitation in a liquid will first be discussed without con- 

 sideration as to whether the liquid is flowing or at rest. On the assumption 

 that a liquid is fractured when the gap between molecular layers is of the 

 order of one molecular radius, computation of the work required to bring about 

 and maintain this separation gives values of the order of 10,000 atmospheres 

 as the breaking strength of water. 23 This result is known to be at least an 

 order of magnitude too high. Various experimenters have reported values rang- 

 ing from 4 atmospheres to estimates as high as 1 ,000 atmospheres. However, it 

 is now recognized that these discrepancies are associated with the air and 

 particle contents of the specimens, the treatment of the liquid before testing, 

 and the experimental methods used. For a critical examination of the various 

 methods and the results reported, reference may be made to Reference 2k. 



