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. 
(V c ). 
7 
Velocity 
per sec- 
ond by 
meter. 
( v m ). 
8 
Velocity 
per sec- 
ond by 
weir. 
(V w ). 
9 
Vc-V m 
10 
Vc-Vw 
(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. 
1.05 Cip. 1 .. 
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 
Feet. 
Feet. 
1.295 
1.735 
2.09 
2.97 
3.37 
Per cent. 
Percent. 
—3.8 
do 
2.84 Rect. 2 
.1 
—2.0 
do 
do 
2.4 
—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... 
Curves 
do 
.....do 
do 
do 
do 
do. 
do 
Int.? 
"id.bcip. i !.!!!!!.!!! ! 
29 
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 
30 
do 
8.02 Rect. s 
6tenths 3 
.3 
2.7 
30 
do 
do 
do 
do 
do 
do 
do 
do 
4.99 Rect. if 
3.6 
30 
4.2 
30 
6.8 
30 
.9 
30 
.7 
30 
4.9 
30 
4.6 
30 
4.8 
(9) 
2.5 
do 
do 
do 
do 
do 
do 
do 
. .do.. . 
—2.0 
3.2 
2.6 
5.0 
3.3 
1.8 
.7 
3.4 
1 Cipolletti 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. 
» Rating curve developed by meter measurements. Velocity taken from curve. 
6 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. 
9 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. 
