6 BULLETIN 854, TJ. S. DEPARTMENT OF AGRICULTURE. 



WEIRS. 



For use in measuring the water entering into and discharging from 

 the tile line, brass, triangular-notch weirs were used, the notch angle 

 being 90 degrees (PI. II, fig. 1, and PL III, figs. 1 and 3). For tile 

 over 4 inches in diameter, weirs with J-inch lips were used; while 

 for thfe 4-inch tile, knife-edged weirs were deemed the most accurate. 

 The weir plates, both of which were set level, were so placed that the 

 nappe of each weir cut free and was fully aerated. 



To determine the discharge over the weirs, V. M. Cone's formula, 



Q = 2.487# 2 - 4805 



w T as used in all computations. In this formula, Q = discharge in 

 cubic feet per second and H = head in feet on weir notch. 



HOOK GAGES. 



Boyden hook gages were used to determine the head on the weirs. 

 On both gages the vernier plates were securely fastened and bradded 

 to the gage, so as to eliminate any error due to possible charge of 

 position of the plates. Each gage was set at a distance of over 2 H to 

 the side of the weir so as to record the correct head on the weir. 



FLUME. 



In order to test the carrying capacity of the tile bedded in earth 

 as in actual practice, a continuous w x ooden flume (PL IV) 570 feet 

 long, 2 feet wide, and 2 feet deep was constructed of 2-inch plank. 

 All joints and seams were calked with oakum and covered with pine 

 pitch to make the flume water-tight. This continuous channel or 

 flume was supported on yoke blocks suspended by f-inch steel rods 

 (A, PL V) from 6 by 6 inch caps (B, PL V) which rested on 4 by 4 

 inch vertical posts (C, PL V). Two vertical posts with their yoke 

 block formed a bent; the bents were spaced 8 feet apart. In all, 

 72 bents were erected. Each bent was braced by 4 by 4 inch posts 

 (D, PL V). 



METHOD OF CHANGING GRADE. 



The upper 6 feet o'f the steel rods were threaded with 10 threads 

 to the inch. For support on the caps, bearing plates with ogee 

 washers and 2-inch hexagonal nuts were used. To raise the flume 

 an inch at any bent it was necessary to turn the nuts just 10 revo- 

 lutions. Ordinary wrenches were cumbersome and slow for turning 

 these nuts, consequently specially-constructed socket wrenches 

 (PL VI, fig. 1) were used, consisting of hollow pipes so shaped as to 

 fit over the nuts and with circular disk handles. This type of wrench 

 greatly facilitated the work of changing grade. 



1 Journal of Agricultural Research, U. S. Department of Agriculture, Vol. V, No. 23, p. 1083. 



