64 BULLETIN 852-, U. S. DEPAETMENT OF AGEICULTUEE, 
pipes, the hydraulic radius is given instead of the diameter, but the 
diagram may be used directly for pipes, since B = ~ri that is, the 
hydraulic radius of a 6-foot pipe is j= 1.5 feet. 
THE WEISBACH FORMULA (6, P. 6). 
For those who wish to use this rather popular textbook formula, 
the following values of/ are suggested, presupposing the use of some 
factor of safety about as listed on page 54. 
Class 1. /= 0.040 for pipes up to 24 inches in diameter. 
7=0.030 for pipes from 26 to 42 inches in diameter. 
Class 2. /=0.030 for pipes up to 18 inches in diameter. 
/=0.025 for pipes from 20 inches to 36 inches in diameter. 
Class 3. /=0.020 for pipes up to 48 inches in diameter. 
/=0.015 for pipes more than 48 inches in diameter. 
Class 4. /=0.015 for pipes up to 48 inches in diameter. 
7=0.012 for pipes more than 48 inches in diameter. 
THE WILLIAMS-HAZEN FORMULA (7, p. 6). 
This formula, being made elastic by varying coefficients, applies 
very closely within the usual range of velocities. The following 
values of C w are suggested, presupposing the use of factors of safety 
as listed on page 54. For velocities exceeding 5 feet per second use 
a coefficient of C w about 10 lower. 
Class 1. C w = 90. 
Class 2. GV=110. 
Class 3. C w =120. 
Class 4. C w =140. 
THE MORITZ FORMULA (9, p. 7). 
The results of the experiments show that the lines of differentia- 
tion between classes of concrete surface may be slightly at variance 
with those suggested by Moritz (see p. 7). A pipe constructed in 
place with steel forms may have very appreciable shoulders at the 
ends of the "set-ups," while a jointed pipe may be very smooth at 
the joints as well as through each unit, 
As shown on Plate VI and on page 47, the exponent of D, the velocity 
is more nearly 2 than 1.S0; therefore the application of the Moritz 
formula changes with the velocities rather than with the diameters, 
since his exponent of d or D, the diameter, practically agrees with 
that of the writer. 
