18 BULLETIN 854, TJ. S. DEPARTMENT OF AGRICULTURE. 



For determining the velocity, coloring matter can be used success- 

 fully only in clear water. Potassium permanganate as well as dyes 

 of all colors were tried in muddy water having a large velocity and 

 it was found practically impossible to detect the colors. However, 

 the voltmeter method may be used equally well in muddy and in 

 clour water for determining the velocity. It is believed that veloc- 

 ities obtained by the use of either color or voltmeter will be quite 

 accurate if the mean of several readings is taken. 



RESULTS OF OBSERVATIONS. 



Tables 3,4, and 5 give the results of the tests. The various series 

 are arranged in ascending sizes of tile and ascending grades. Table 

 3 gives the results of observations on clay tile; Table 4, the results of 

 observations on concrete tile; and Table 5, the results of observa- 

 tions on clay tile poorly laid. The Kutter coefficient of roughness, 

 n, given in column 10, was determined from a large diagram specially 

 drawn for this investigation. The variation and irregularity of 

 the joints of the tile in the lines poorly laid can be seen in Plate 

 VIII, figure 2. 



The tests summarized in Tables 3 and 4 were plotted on coordinate 

 paper, with velocities as abscissae and depths of flow as ordinates. 

 Mean curves were drawn for each grade through the points repre- 

 senting the tests for each size and kind of tile. These curves are 

 shown on Plate IX. A study of the curves reveals some interesting 

 facts. For the flatter slopes the curves more nearly approximate a 

 straight line; as the slopes increase the lines become more curved, 

 until at the steepest grade there is considerable bulge to the curve. 

 The velocity at any depth of flow over half full is shown at a glance. 

 It will be noted that the velocities at half full and at full are seldom 

 the same, as they would be according to the Chezy formula. The 

 greatest velocity seems to be approximately at the 0.8 depth. The 

 curves were not extended below the half -full point on account of the 

 insufficiency of data. In the largest sizes of tile, where symbols are 

 shown but no curves have been drawn, incompleteness of data has 

 prevented the development of accurate curves through these points. 

 It will be seen that with some of the curves the points lie practically 

 on the linos, while with other curves some points vary greatly, show- 

 ing probable error in the experiments. 



