24 BULLETIN 376^ U. S. DEPAKTMENT OF AGEICULTURE. 



for four injections of color in a pipe carrying up to 60 second-feet, 

 while in the 13^-foot pipe (No. 52) the total contents of the "fluor- 

 escein gun" (fig. 3) were injected at one time, and for the volume 

 of water carried in this pipe (the maximum was 871 second-feet) a 

 saturate solution was used. Though not measured, this consisted 

 of about 4 teaspoonsful of the powder for each "shot" of about one- 

 third pint. The powder dissolved readily in cold water. 



In making a test the coupling W is opened and the solution poured 

 into the pressure tube X. The gun is again connected with the 

 apparatus by the coupling W. With E closed V is opened. Pressure 

 in the wood pipe enters the gun, making pressures in both gun and 

 pipe equal. In order to inject the color into the pipe the only thing 

 necessary is to increase the now existing pressure in the gun. After 

 V has been closed the gun is pumped up like a bicycle tire. While 

 noting the time to a second the operator opens the cock V. By 

 the hissing sound, it is probable that the jet passes well across the 

 diameter of a medium-sized pipe. If the contents of the gun are to 

 cover three or four injections V is opened and almost immediately 

 closed. If all the contents are to be used a few quick strokes of the 

 pump, after V has been opened, will clear the gun in a very few 

 seconds, the mean time being accepted in later computations. 



The observer at the outlet, provided with a watch agreeing to the 

 second with that used in timing the start of the color, notes to the 

 second the first and last appearance of the color.- The color is ex- 

 tended by the variation in the velocity throughout the section of 

 the pipe. This extension covers about 8 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 

 also 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 1. 



