559 



in conceritrations that would be negligiljlc or beneficial in the case of 

 carbon dioxide. 



Properties of the Gases 



Carbon monoxide is Hghter than air, having a specific gravity of 

 0.967. It is odorless, tasteless, and colorless, burns with a char- 

 acteristic pale blue flame, forming carbon dioxide, and is only slightly 

 soluble in water, 23.1 c.c. dissolving in a liter at 20°C. 



Carbon dioxide is heavier than air (specific gravity 1.519J, is 

 odorless, has a decidedly acid taste, is colorless at ordinary tempera- 

 tures, and will not burn, since the carbon atom already holds' in com- 

 l^ination all the oxygen with which it has the power to combine. It is 

 ^■ery soluble in water, a liter of water at ordinary temperatures hold- 

 ing in combination almost a liter of the gas. The carbon dioxide does 

 not simplv dissolve in the water, but unites with it to form carbonic 

 acid (C02+HoO=H2C03). 



Methods and Materials 



Two types of experiments have been made, one to determine the 

 resistance of the fishes to the gases in variovis. concentrations, another 

 to determine the reactions of the fishes to the gases in the gradient. 

 The latter type gives the fishes an opportunity to select or reject the 

 water containing the gas. The fishes were collected in the small 

 streams of northern Illinois, fifteen to twenty different species having 

 been tested more or less fully. 



Resistance B-vperiments. — A paper (Wells, '13) has already been 

 published which gives the detailed methods and observations concern- 

 ing the resistance of fresh-water fishes to carbon dioxide. Briefly, 

 the experiments were made as follows : — A stream of water flowing 

 at a rate of from 500 — 600 c.c. per minute was passed through two 

 experimental bottles having a capacity of seven and three liters re- 

 spectively. The gas was introduced into the flow at a point far enough 

 away to allow it to dissolve before it reached the bottles. The exact 

 concentrations of CO^ in the experiments was determined by titration 

 of samples collected as the water flowed out of the experimental bottles. 

 These determinations were made at regular intervals throughout each 

 experiment. 



The resistance experiments with carbon monoxide were made much 

 as were those just described for carbon dioxide. The method of 

 determining the concentration of the gas in the collected samples was 

 that described in Hempel's "Gas Analysis".* The gas was boiled off 

 and absorbed with a hydrochloric acid solution of cuprous chloride. 



*Heiiipers "Gas Analysis," 1910 edition, p. 203. 



