THE FLOW OF WATER IK 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 Wis 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 seoond 

 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. 



