8 BULLETIN 376. U. S. DEPARTMENT OF AGRICULTURE. 
has persisted that there is less friction in wood pipe than in metal 
pipe. It has often been insisted that new wood pipe not only has 
a higher carrying capacity than new metal pipe but that the wood 
pipe becomes smoother with age. while it is a well-known fact that 
metal pipe becomes rougher. (See discussion, p. 72.) 
While the analysis of all the tests on wood pipe now available bears 
out the above claims in a general way (excepting that wood pipe 
is not showu to become smoother with age), yet the consideration 
of tests on individual pipes led to hasty conclusions presently shown 
to be greatly at variance with facts. The following ideas of hydrau- 
licians have been extracted by the writer from all the literature on 
the subject known to him: 
The experiments of Darcy and Bazin in 1857 and 1859 (Nos. 22 
and 33) and of Clarke in 1884 (No. 49) were considered but little in 
later discussions for the reason that they were made on rectangular 
rather than on round pipe. Smith's test (No. 1), made in 1877, 
has also not been considered in the discussion of wood pipe, as the 
test was made on a bored pipe of very small caliber: yet these four' 
series supplied the data upon which Tut ton based his formula. (See 
p. 50.) 
Although none of the 81 tests considered by Kutter and his col- 
league in developing the Kutter formula had been made on closed 
channels r unn ing full, yet nearly all of the experimenters on wood- 
stave pipe have determined for their tests the value of n hi this 
formula. Kutter s formula has undoubtedly been used a great deal 
in estimating the capacity of wood pipes, but the writer will endeavor 
to show (p. 56) the fallacy of employing a constant value of n in 
this formula and the advantages lying in a formula of the exponential 
type. 
The first experiment of public record was mentioned by the late 
J. D. Schuyler x hi speaking of a test (No. 34) on the newly installed 
30-inch pipe for Denver, but unfortunately he did not give sufficient 
details by which the test might be weighed. Mr. Schuyler states 
that " as low a coefficient of n as 0.0096 can be used." This appeared 
reasonable, as the pipe was made of planed lumber and all lists of 
proper values of n then published recommended a value of 0.009 for 
such material. The earlier designers adopted a value of 0.010 "in 
order to be conservative." 
The next tests were made by A. L. Adams 2 on the Astoria, Oreg., 
18-inch pipe (No. 23). Here, too, a low value of n was found, 0.00985, 
which led Adams to observe "that the value of 0.010 for n used by 
many engineers in dealing with stave pipe, is here found to be practi- 
cally correct." The low value of the friction factor found in this 
i Trans. Amer. Soc. Civ. Engin., 31 (1S94), p. 144. 
2 Trans. Amer. Soc. Civ. Engin., 36 (1896), p. 26. 
