98 BULLETIN" 852, TJ. S. DEPARTMENT OF AGRICULTURE. 



The formula T'=130 i? - 625 s °- 50 was suggested for new pipe (and 

 otherwise with varying value of the coefficient) as being more con- 

 sistent and quite as accurate as some other procedures that had 

 preceded. 



Following this, a simple hydraulic-slide rule was made to calculate 

 pipe friction by it. This permitted a great increase in rapidity of 

 estimate. The writer used these homemade rules for a year or two 

 in his daily work, and made a number of them for his friends. He was 

 well satisfied with the estimates that were reached by their use. Later 

 the interest in hydraulic-slide rules increased, and there was a demand 

 for more of them, and it was decided to have them made in quantity. 

 Before doing this a careful reconsideration of the exponents was made 

 by Prof. Gardiner S. Williams, which led to the adoption of those which 

 have since come to be associated with the Williams and Hazen 

 formula. 



This Williams and Hazen formula was intended to represent more 

 accurately all round average waterworks conditions than the earlier 

 one, which was identical with that one now proposed by the author, 

 and the writer thinks that for such general use it is an improvement. 



It may be pointed out that a slight variation in the exponents does 

 not make a very great difference in ordinary estimates. Precision in 

 the values of the exponents is not to be expected and is not necessary. 

 It is only desirable that the formula that is used should have exponents 

 that do not differ too widely from the actual facts. 



With such a formula the important matter is a study of the coeffi- 

 cients to find out whether these coefficients are affected by variations 

 in the condition and smoothness of pipe surface, and by the character 

 of the water that flows through the pipe. At the present time study 

 of coefficients is much more useful than further study of minute 

 differences in exponents. 



The writer is glad to see that the author is taking up his data along 

 these lines. 



DISCUSSION BY MR. LIPPINCOTT. 



I have had a good deal to do with the construction of large concrete 

 pipes, 10 to 12 feet in diameter, and the folio whig observations may 

 possibly be of interest : 



Concrete will expand and contract with wetting and drying in 

 much the same way that it does between heat and cold, and in order 

 to prevent shrinkage cracks coming from drying, the concrete pipe 

 or conduit should be kept just as moist as possible during the period 

 in which it is curing and until it has been actually put into service. 

 In the case of large pipe particularly this can be accomplished by 

 putting some water into the pipe and by closing the ends of the pipe 

 after it is built so as to prevent the circulation of dry air through 

 the pipe. I have known concrete pipe that has developed circular 

 shrinkage cracks which leaked badly when water was first put in and 

 to close up after the water had been running through them for seven 

 or eight days, I believe because of the expansion of the concrete due 

 to its becoming saturated. 



By taking pains in the manner suggested with the construction of 

 the Los Angeles Aqueduct in the Mojave Desert, preventing the 

 drying out of the concrete by circulation of air, mile after mile of 

 this ditch could be built without any expansion joints and without 

 any cracks developing. 



