102 
Journal of Agricultural Research 
Vol. IX, No. 4 
'f xl f 
there was ho appreciable change, but occasionally there was a change 
amounting to a few ten-thousandths of an inch. 
In some of the experiments, where the greatest quantities of water 
passed through the orifice, there was a tendency toward vortexes. The sur¬ 
face of the water immediately up¬ 
stream from the orifice would take 
a whirling motion with a greater or 
less depression, but the funnel never 
was sufficiently complete to allow 
air to be drawn through the orifice. 
The effect of these vortexes upon 
the discharge through the orifices 
was not apparent under the con¬ 
ditions of the experiments, but it 
might amount to considerable with a smaller depth of water in the 
channel of approach. 
STANDARD CONDITIONS AND DIMENSIONS FOR SUBMERGED 
RECTANGULAR ORIFICES WITH MODIFIED CONTRACTIONS 
As a result of experiments with several different arrangements the 
conditions described below and illustrated in figures 12 and 13 were taken 
as the standard because they appear to give the most reliable results, 
meet the practical demands for a measuring device of this type, and 
reduce the cost of construction. 
Fig. 6 .—Elevation and sections of broad-edged 
orifice. 
Fig. 7.—Elevation and sections of broad-edged orifice 
with wood gate guides. 
It is essential that the orifices 
and orifice boxes be built accord¬ 
ing to these specifications if the 
discharge formula or table is to 
be used. The influence of vari¬ 
ous changes in the size of the box 
and arrangement of the orifice is 
shown in Table I. 
The total length of the orifice 
box is 16 feet, 10 feet of which 
forms the channel of approach. 
Wings set at an angle of 90° are attached to the sides of the upstream 
end of the orifice box. The floor of the box is level throughout and at 
the same elevation as the bottom of the canal. The box should be set 
in the center line of the canal, so as to allow the water to enter the box 
in straight lines. The sides are parallel and are placed apart a distance 
equal to the length of the orifice plus 2 feet. Orifices of all sizes have 
end-contraction distances of 1 foot. 
The orifice must have sharp sides and top, and no bottom contraction. 
Angle irons 1 inches wide were used in the experiments and were placed 
as shown in figure 3. The orifice must be placed with its greatest dimen- 
