REACTIONS OF FISHES TO SALTS 245 



the same condition and fishes can live in either after the proper 

 amount of aeration. Too much aeration causes the lUinois 

 water to become alkaUne to phenolphthalein and fresh water 

 fishes cannot hve in such water. 



III. METHODS AND APPARATUS 



The reaction experiments have been performed in the gradient 

 tank used in the acid gradient experiments (Wells '15 a, fig. 1, 

 p. 223). 



The salts used have been, the chlorides, nitrates and sulphates, 

 of ammonium, potassium, sodium, calcium and magnesium. In 

 presenting the results of the reaction experiments the salts will 

 be grouped with reference to the anion, as the similarities in 

 behavior, in the different salt gradients, make this a rather natu- 

 ral division. They will also be taken up in the order of increas- 

 ing toxicity of this ion as worked out by Lillie ('10) and others. 

 Thus the order of consideration will be, chlorides, nitrates, sul- 

 phates. In considering the resistance experiments, on the other 

 hand, the salts wdll be grouped according to the kation. In 

 the gradient experiments the concentration of salt introduced 

 at the salt end has been in nearly all cases 0.01 X. In a few 

 experiments the concentration was made 0.02X or even higher 

 in an attempt to drive the fishes out of the salt end, to which they 

 were giving a positive reaction. These experiments will be 

 cited as they come up. 



The gradient in the salt experiments was obtained as follows: 

 Tap water was set to flowing into one end of the tank at the 

 rate of 500 cc. per minute, and into the other end at the rate of 

 400 cc. per minute. A 0.05 X solution of the salt was made up 

 with tap water and run into the flow at the 400 cc. end at the 

 rate of 100 cc. per minute. This made the volume of the flow 

 at the two ends equal. The salt solution was mixed with the 

 tap water, in a mixing bottle, outside the experimental tank. 

 From the mixing bottle a single outlet led to the experimental 

 tank. At first the gradients were tested before and after each 

 experiment. Later, after a very careful study of the gradient 



