90 BULLETIN 852, TJ. S. DEPAKTMENT OF AGRICULTURE. 
area on the sides of the sewer. The incrustation seemed slightly 
heavier, but the organic growth did not show any marked increase 
over that at the time of the 1897 tests. 
In his discussion Mr. Horton accepts the value of n of 0.0117 for 
1896, of 0.0127 for 1897, and of 0.0133 for 1900. (See Table 11, p. 69 
for individual values of each observation.) He notes that the de- 
posits of grease and of organic matter were greatest on the sides, 
especially near the line of average flow; that the bottom was clean 
scoured by sand and other heavy particles. 
In his discussion on these experiments, Rudolph Hering mentions 
several cases where the deposit exceeded that noted by Horton. 
Mr. G. C. Whipple brings out the point that the organisms which 
grow in sewers are vegetable forms of a very low type, while those 
found in water pipes belong to the animal kingdom — fresh-water 
sponges, etc. 
The results of these tests would indicate that sewage undoubtedly 
coats a cement surface to such an extent that an exceptionally smooth 
interior surface would not long contribute to a high capacity, as 
would be the case for most clear waters. By the same deposits, 
on the other hand, a very rough interior might be so smoothed over 
that the capacity will be increased, provided the sewage was suffi- 
ciently diluted with surface or other ordinary waters, thus preventing 
excessive deposits. 
Nos. 68, 69, and 70, Experiment H -2.— Basket-handle cement- 
washed brick sewer, North Metropolitan sewerage system, Boston, 
Mass. — Simultaneously with the tests described as Nos. 65, 66, and 
67, Horton also made experiments upon the basket-handle section 
adjoining the circular section. The shape was 6 feet by 6§ feet, but 
otherwise similar in construction to the circular section. The general 
description under the latter applies also to this section. 
The difference in the values of n for the two shapes would indicate 
that a better surface is obtained in a circular form than upon plane 
faces, or those requiring hand troweling. A review of tests for 
carrying capacity shows this fact to be quite general. 
No. 71, Experiment M-4. — Cut-and-cover sections of the Esopus 
division, Catskill Aqueduct, New York State. — Long reaches of the 
Catskill Aqueduct were constructed as flow-line sections, as dis- 
tinguished from the reaches under pressure. 1 These sections are of 
the cut-and-cover type, a concrete horseshoe 17J feet wide and 17 
feet high. 
The invert, 16 inches thick, was laid first, in alternate panels each 
15 feet long. After the forms had been filled — 
The work is screeded with a 16-foot length of 3-inch circular steel shafting, which 
is rolled along the top of the forms, bearing on the web plates and the horizontal legs 
of the angle irons riveted to them. Great care is taken to obtain a smooth finished 
surface. 
For the walls and arch, steel forms in 5-foot units bolted into 15- 
foot sections were used. From invert to arch any one section was 
completed at one pouring. After the oiled forms were in position, 
four men crawled between the forms, two on each side. As the 
concrete, a wet mix in a ratio of about 1 to 3 to 5, was poured in 
1 Engin Rec. vol. 61 Jan. 8, 1910; vol. 62, Nov. 5, 1910; Water Works Handbook, Flinn, Weston and 
Bogert, New York, 1916, p. 271. 
