COEFFICIENT OF FRICTION FOR PIPES. 193 



+ 8 Z 2 (W 4 t /j 



Now if the pipe is cylindrical, j3 = 0.505, from Cor. 3 

 of Art. 69, and therefore we have 



- 1 _J? 1 - 505 

 2g 64$ 



= .0234, 



and taking a^ = .00007 and 2 = .00042,* and substi- 

 tuting these values in (5) and reducing, we have 



/%38Qhd I 



'' V I + 54rf~ 12(Z + 54d)' 



COB. When h is not very small, the last term of (6) may 

 be neglected, and we have 



2380M 



which is very nearly the same as (8) of Art. 104. 



When the pipe is very long, d is very small compared 

 with I, and (6) becomes 



: s* (8) 



When d is expressed in inches and all the other dimen- 

 sions in feet, (8) of Art. 104 becomes 



I + 4. 



(9) 



SCH. The following short table gives Weisbach's values 

 of the coefficient of friction for diiferent velocities in feet 

 per second : f 



* Tate's Mech. Phil., p. 298. 



t Ency. Brit., Art. Hydromechanics. 



