18 



BULLETIN 852, U. S. DEPARTMENT OF AGRICULTURE. 



Current meter. — -Where the water entered or left the pipe in an open 

 channel the discharge was determined with a current meter, and the 

 velocity in the pipe was secured by dividing this discharge by the area 

 of the pipe. The two-tenths and eight-tenths depth method was used, 

 as the results obtained in this way, when compared with the discharge 

 found by the multiple-point method, generally agree with it to 

 about 1 per cent. 



Table 2. — Velocities by color compared with velocities by weir and current meter. 



1 



Pipe 

 No. 



2 



Ref. 



No. 

 (Bul. 

 376). 



3 



Pipe 

 diam- 

 eter. 



4 

 Crest length of weir. 



5 

 Meter method. 



6 



Velocity 

 per sec- 

 ond by 

 color. 



7 



Velocity 

 per sec- 

 ond by 

 meter. 

 ( V m ). 



8 



Velocity 

 per sec- 

 ond by 



weir. 



(V w ). 



9 

 V c - V n 



10 

 Vc-V w 



(this 

 bul.). 



V c 



V c 





60 

 61 

 62 



63 

 64 

 132 

 192 

 193 

 194 

 263 

 264 

 265 

 266 

 ( 6 ) 

 269 

 270 

 271 



Ins. 



8 

 8 

 8 

 8 

 8 

 18 

 48 

 48 

 48 

 78 

 78 

 78 

 78 

 78 

 78 

 78 

 78 

 36 

 36 

 42 

 42 

 42 

 42 

 42 

 42 

 42 

 42 

 42 

 36 

 36 

 36 

 36 

 36 

 36 

 36 

 36 

 36 



Feet. 

 1.05Cip.i 



, 



Feet. 

 1.251 

 1.736 

 2.048 

 3.043 

 3.294 

 2.08 

 3.14 

 3.75 

 4.75 

 .911 

 .963 

 1.51 

 2.063 

 2.16 

 2.40 

 2.44 

 2.79 

 3.48 

 3.48 

 1.007 

 1.19 

 1.41 

 1.66 

 1.75 

 1.96 

 2.24 

 2.53 

 2.91 

 1.17 

 1.22 

 1.89 

 2.69 

 2.75 

 2.90 

 2.99 

 3.74 

 3.80 



Feel. 



Feet. 



1.295 



1.735 



2.09 



2.97 



3.37 



Per cent. 



Per cent. 

 —3.8 





do 









.1 





2.84 Rect. 2 









—2.0 





do 









2. 4" 





do 









-2.4 







6 tenths 3 



2+8* 



1.99 

 3.05 

 3.71 

 4.73 

 .928 

 .974 

 1.60 

 2.08 

 2.10 

 2.37 

 2.42 

 2.51 

 3.48 

 3.55 



4.3 



2.9 



1.1 



.4 



-1.9 



-1.1 



-6.0 



-1.0 



2.8 



1.2 



.8 



3.1 



.0 



-2.0 

















do 











do 











Curved 



do 



















do 











do 











do... 











...do .. 











do 











...do... 







29 



lO.OCip.i 



Int. t ... 



3.47 

 3.47 

 .980 

 1.147 

 1.351 

 1.547 

 1.734 

 1.947 

 2.130 

 2.414 

 2.769 

 1.141 

 1.245 

 1.830 

 2.619 

 2.612 

 2.805 

 2.935 

 3.713 

 3.669 



.3 



29 



do 



6 tenths 3 



.3 



30 



8.02 Rect. s 



2.7 



30 



do 







3.6 



30 



do 









4.2 



30 



...do 









6.8 



30 



do 









.9 



30 



do 









.7 



30 



do 









4.9 



30 



do 









4.6 



30 



....do 









4.8 



( 9 ) 



4.99 Rect. 1" 









2.5 



do 









—2.0 





do 









3.2 





do 









2.6 





do 









5.0 





do 









3.3 





do 









1.8 





do 





" 





.7 





....do 









3.4 















1 f'ipolletti weir with good conditions of contraction and velocity. 



2 Rectangular weir with end contractions and sharp crest. 



3 Meter held in each vertical at 0.6 depth from surface. 



* Meter held at 0.2 and 0.8 depths in each vertical; mean accepted for vertical. 



6 Rating curve developed by meter measurements. Velocity taken from curve. 

 « Excluded from Table 2, Bul. 376, because gauge data lost for manometer No. 1. 



7 Velocity integrated by moving meter slowly from top to bottom and return. 



8 Indeterminate velocity of approach. Crest rounded. 

 8 Experiments on 36-inch lock-bar steel pipe. 



10 Rectangular weir with suppressed contractions at both ends. Velocity of approach indeterminate. 



Color. — Three chemicals were used in making powerful colors — 

 fluorescein, Congo red, and potassium permanganate. About 1 tea- 

 spoonful of fluoreacein (in the form of red powder) mixed in about a 

 pint of water gave sufficient solution for four injections of color in a 

 pipe carrying up to 60 second-feet. The powder mixed readily in 

 cold water. Congo red is used in the same way, but about 10 times 

 as much "red" is recessary to obtain the same intensity of color. 



