DESCRIPTION OF PROCEDURE 



The experiments were carried out in the 1/22-scale model 

 of the circulating water channel of the Taylor Model Basin 

 (Figure 2)„ The test section is 12 inches across and the water 

 was about 6 inches deep during the experiments The velocity 

 used was about 1 6 ft /see 



At the entrance to the test section a brass grid was placed 

 as a source of turbulence «, The mesh width was Oo75 in„ and the 

 wire diameter o l5 in, A length of brass tubing, inside diameter 

 Oo035 in,,, outside diameter 0„060 in Q §, was then placed in the 

 test section in the manner shown schematically in Figure 1 G The 

 downstream end of the horizontal section of the tuning was located 

 15 and 22 mesh lengths from the grido The other end of the tubing 

 eventually led to a jar containing the dye to be used In order 

 to be able to control the rate of flow of dye through the tubing 

 the jar was connected with a flask of compressed air equipped 

 with a valve Measurement of the discharge rate showed that the 

 average velocity through the release tube was about 2 2 ft/sec. 



To measure the average concentration of dye at positions 

 downstream from the end of the dye release tube, a 3=in length 

 of the same brass tubing was attached to the movable sampler 

 shown in Figure 3« This probe was rigidly clamped to the channel 

 carriage in a position such that the samplar lay in the same 

 vertical plane as the release tube» By means of the probe 

 micrometer screw, this sampler could be traversed vertically in 

 any desired increment with an accuracy of o 001-in<> to a total 

 displacement of 3 in„ In order to extract a sample of water 

 from some position downstream of the release tube a 25 cc pipette 

 was connected to the sampling tube by means of a short length of 

 rubber tubing and a sample sucked out G Tests with a stop watch 

 showed that the average velocity of the water passing through the 

 end of the sampling tube was about 5 ft/sec 



The dye solution used in these experiments was made by 

 dissolving about 1 gm of Ponceau red, a water-soluble food dye, 

 in 4 liters of water Q The concentration of a sample was measured 

 by means of a Fisher Electrophotometer Such measurements are 

 generally considered to be accurate to about 1 percent,. No series 

 of experiments to determine the accuracy of this instrument was 

 made since the exploratory nature of the setup did not seem to 

 warrent them In order to determine whether the length of time 

 over which a given sample was taken was sufficient to give a con- 

 centration close to the average concentration at that point, 

 several of these samples were taken twice „ The maximum changes 

 were of the order of 8 percent In order to take account of the 

 gradual coloring of all the water in the channel, a sample of 

 the channel water was also taken after every set of five measure- 

 ments o The correction for the darkening of the channel water was 

 surprizingly little considering how noticeable the coloring was 



to the eye„ 



- 3 - 



