REACTIONS OF FISHES TO SALTS 253 



3. Reaction to sulphates 



a. Ammonium sulphate. Fishes are negative to this salt as 

 to the other ammonium salts. All the ammonium salts are 

 strongly toxic to the fishes used. Especially is this toxic reaction 

 noticeable in the tap water. The explanation for this will be 

 taken up in the discussion of the resistance of fishes to ammonium 

 salts. 



h. Potassiu7n sulphate. Fishes are decidedly negative to 

 O.OIN concentration of potassium sulphate. Twelve experi- 

 ments were performed in moderately acid water and in none 

 did the fishes give a positive reaction. In one the fish selected 

 the middle third of the tank, but turned back regularly from the 

 salt end. The results with this salt illustrate the increasing 

 toxicity of the anion; it will be remembered that in moderately 

 acid water the fishes gave a positive reaction to the nitrate of 

 potassium. No experiments w^ere performed at Chicago with 

 this salt. 



c. Sodium sulphate. No experiments were performed at 

 Chicago with this salt. At Illinois tw^o series were run, one in 

 moderately acid water, and the other in strongly acid water. 

 The reactions in the two kinds of water were very similar to those 

 obtained with sodium nitrate in the same kinds of water. It 

 was noted that in the strongly acid water the fishes often spent 

 much of the time at the surface and were thus not swimming in 

 the strongest gradient. For this reason the reactions might 

 be expected to be somewhat less definite but the results show very 

 little difference in cases where the fishes stayed at the bottom 

 or swam at the surface. In 4 experiments the fishes spent 

 practically all the time at the surface and 60 to 90 per cent in 

 the salt half of the tank. In 8 experiments with this strongly 

 acid water the fishes remained at the bottom throughout; seven 

 of these experiments show a decided preference for the salt end 

 while one was negative. 



In the NaNOs experiments, it will be remembered, the fishes 

 were negative to the .salt in moderately acid water and this 

 was also found to be the case with the sulphate. Fifteen experi- 



