mo 



the amount of iodine absorbed appeared to bear no definite relation 

 to toxicity. It is probably best to determine the toxicity of waste with 

 fishes rather than by chemical means. 



I. METHODS OF EXPERIMENTING WITH WASTE. 



a. Standing water. 



Battery jars 5 inches in diameter and 8 inches deep are filled to a 

 depth of 4 inches (10 cm.) with waste diluted for use. This gave 

 2,000 cc. of liquid with 113 sq. cm. of exposed surface and gave con- 

 ditions under which one or two fishes would live for days. This 

 method simulated in a general way the conditions in polluted standing 

 water. The period of toxicity determination being one or two hours 

 the method was free from serious objections. 



h. Running Water Method. 



A bottle with a very w^ide neck, holding a liter is fitted with a rub- 

 ber stopper in which are three holes (M. Fig. i). A 12 liter aspira- 

 tor bottle (Fig. I W) with stopper lubulature is closed at the bottom 

 aperture and filled with waste about ten times as strong as is required 

 for the experiment at hand. One part of the diluted waste is run into 

 the bottle through one opening in the three holed rubber stopper, while 

 9 parts of water are introduced through another. The water flows 

 from this bottle into a larger bottle holding about three liters, in which 

 the fishes were confined. The flows were set with pinch cocks on 

 rubber tubing and adjusted from time to time. The flows used varied 

 from time to time but usually were between 100 to 300 cc. per minute. 

 The object was to secure definite concentrations rather than definite 

 flows, as all that is necessary is to change the water often and simulate 

 the conditions in running streams. The temperature of such experi- 

 ments was usually i/°C. 



c. Bottle method. 



For determining the exact toxicity of any sample of waste when 

 unexposed to the air it is necessary to proceed in an entirely different 

 way. A bottle with a wide mouth, holding a little more than four 

 liters, is supplied with a close fitting rubber stopper. It is first filled 

 with water to the four liter mark scratched on the outside. A definite 

 amount of w^aste is then run in from a burette or Mohr's pipette. The 

 bottle is then shaken until all of the substance is in solution. The 

 free air space, which should not exceed 2% of the volume of the 



