Flow of Ground Water. 203 



od 2 a 

 q = 10.22 --T c. c. per second (1) 



where 



p is the pressure in c. m. of water at 4 C. 

 d is the diameter of the soil grains in millimeters. 

 s is the area of the cross-section in sq. c. m. 

 H is the coefficient of viscosity. 

 h is the length of the column. 



k is a constant whose log. is taken from the table, p. 123. 

 and 10.22 is a constant whose log. is [1.0094.] 



If the pressure is measured in feet of water at 4 C., the 

 length in feet, the area of cross section in square feet, the 

 time in minutes and the diameter of the soil grains in mil- 

 limeters the formula is 



q = .2012 -^YF cubic feet per minute - ( 2 ) 



If the flow of water occurs under a temperature of 10 

 C. or 50 F. the formula may be written 



T)d 2 S 



q = 15.30 F cubic feet per minute. (3) 



Problem. A cylinder 4 feet long, having a cross sec- 

 tion of 2 sq. ft., is filled with sand whose grains have an 

 effective diameter of .15 mm. What will be the flow of 

 water through it under an effective pressure of 12 feet, 

 when the temperature is 50 F. and the pore space is 35 

 per cent. ? 



Substituting these values in equation (3) we get, taking 

 the value of k from the table, page 123. 



15.3 ,o.o = -06532 cu. ft. per minute. 

 4 x ol.bJ 



Problem. What would be the flow in cubic feet per 

 minute under the same conditions except at a temperature 

 of 68 instead of 50 F. ? In this case use formula (2) 

 and the results are, taking the coefficient of viscosity at 

 68 F. at .0101 from the table below: 



