THE FLOW OF WATER 1ST CONCRETE PIPE. 
17 
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DETERMINATION OF LOST HEAD. 
The exact amount of 7i t (fig. 1) must be determined. Where a 
water column is used, say at gauge No. 2, the elevation E 2 is the 
gauge reading added to the elevation of the gauge zero above an 
assumed datum, with proper corrections (see p. 5). Where a 
mercury manometer of the U-tube pattern is used, the reasoning is 
as follows: It is desired to know the elevation E 1 (fig. 1) for a water 
column which is the equivalent of a mercury column in a U-tube 
placed as for gauge No. 1. 
Referring to figure 2, the 
mercury in the two legs of 
the U-tube below Q will 
be seen to balance. There- 
fore the pressure of the 
water at Q is just balanced 
by the column of mercury 
QT. But the pressure at 
c equals that at d. If the 
mercury X were replaced 
with water it would reach 
an elevation sR above Q, 
where s is the specific 
gravity of the particular 
mercury in the gauge, 
compared with the par- 
ticular water in the pipe. 
But the elevation to which 
this water column would 
reach is the desired eleva- 
tion, E v As applied to 
these experiments, refer- 
ring to figures 1 and 2, the 
difference in elevation be- 
tween the readings of the 
low gauge and the high 
gauge multiplied by the 
specific gravity of the mercury and added to the elevation of the 
low-gauge readings gave the elevation of the equivalent water 
column when the proper corrections had been applied. 
MEASUREMENT OF MEAN VELOCITY. 
As a rule, each pipe tested presented its own problem as to the 
method to be adopted to determine the mean velocity of the water, 
and in case this method digressed from one of the following standard 
methods it is described. 
164725°— 20— Bull. 852 2 
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Note; In abore figures the piezometers ore relatively forffe. 
Fig. 3.— Various arrangements of piezometers for securing 
pressure head at a given place on the pipe line. 
