THE PLOW OF WATEK IN CONCRETE PIPE. 19 
In the use of potassium, a handful of the crystals made about 2 quarts 
of dense color. Cold water quickly attains a saturate solution if well 
stirred (from 5 to 8 per cent by weight at ordinary air temperature) , and 
may then be poured off the undissolved crystals, which do not float. 
About 1 pint of solution will color 50 second-feet of clear water. 
Some waters break down the color to a muddy brown, which is 
unsatisfactory. 
In making a test the coupling W (fig. 2) is opened and the solution 
poured into the reservoir S. After W is closed the gun is pumped up 
like a bicycle tire. Noting the time to a second, the operator opens 
the cock V. 
The observer at the outlet notes to the second the first and last 
appearance of the color. The color is extended by the variation in 
the velocity throughout the section of the pipe. This extension covers 
from 8 to 12 per cent of the total time the color spends in the pipe. 
Comparison with carefully constructed weirs shows that the color 
method is correct within about 3 per cent. Wherever possible, a 
comparison between color and current meter was made. To secure 
comparative results, the time the color spent in the pipe is taken as 
from the moment of injection to the mean between first and last sight 
at the outlet. These comparative tests are shown in Table 2. 
All watches used in the tests were compared before and after each 
experiment, corrections being noted for use in computing elapsed 
time. The watch agreeing best with jewelers' chronometers was used 
as the standard. 
FIELD PROCEDURE. 
After the reach of pipe was selected,the manometers attached, and 
other equipment put in readiness, the method for proceeding with 
the field test was in general carried out as described in the para- 
graphs following. Any necessary changes are noted in the text in 
connection with the. description of the individual pipes tested. 
The watches used at both ends of the reach were adjusted to agree 
to the second, and again compared at the end of the observation. 
Manometers were read at intervals varying from 30 seconds to 2 
minutes (depending on the amount of pulsation in the water). If 
a weir was used to measure the discharge of water, a hook gauge above 
the weir was read every 2 to 5 minutes, depending on the variation 
of discharge. If a current-meter measurement was necessary to 
determine the discharge, it was made either during or immediately 
following the series of manometer readings, the manometers being 
watched for appreciable variations of discharge. Where color was 
used to time the actual velocity of the water it was injected into the 
pipe at approximately known intervals, say 5 minutes, throughout the 
time during which the manometers were read. Ordinarily the second 
gauge was near enough to the outlet of the pipe so that one observer 
could both read the manometer and watch for the appearance of the 
color. Sometimes an additional observer was necessary. 
