REACTION AND RESISTANCE OF FISHES. 233 



eral acid itself; yet this will be the only hydrogen ion supply 

 until the bicarbonates have all been changed to sulfate (if 

 sulfuric acid is the mineral acid used). The tap water at Illinois 

 requires approximately 90 c.c. of .1 TV H 2 SO 4 to neutralize the 

 bicarbonates in one liter of water while the Chicago water re- 

 quires about a third as much. According to the above equation 

 one molecule of the acid liberates 2 molecules of COo. There- 

 fore 90 c.c. of .1 TV acid will liberate 210 c.c. of COz. Powers 

 ('13) did not take this reaction into account and speaks of com- 

 paring the reactions of crayfishes in gradients of HC1 and CCV 

 As a matter of fact the amounts of HC1 which he added to the 

 Chicago tap water were probably used up in neutralizing the 

 bicarbonates. Thus all his gradients were with carbonic acid, 

 and the differences which he gets are due to the liberation of 

 this acid in excess, in the reaction of the HC1 and the bicar- 

 bonates. 



(1) H%SOi to Neutralize all Bicarbonates vs. Neutral Water. 

 The CC>2 liberated in this gradient made the water so acid that 

 the fishes were soon overcome, and died if not removed from the 

 tank. However at first they gave a decidedly negative reaction 

 to the acid end. 



(2) H 2 SOt to Liberate 40 c.c. CO Z per Liter vs. Neutral Water. 

 The fishes reacted much as they did in gradients of aerated 

 vs. unaerated water. They were very negative to the acid 

 end. 



(3) H%SOi to Liberate 4 c.c. C0 2 per Liter vs. Neutral Water 

 (Graphs 4 and 5, Chart /.). Eighteen experiments of this sort 

 were run. Of the 18 graphs, 14 show that the fishes spent 90 

 per cent, of the time in the acid half of the tank; 3 show more 

 than 50 per cent, of the time in this half and I (small blue-gill) 

 shows an 80 per cent, preference for the neutral end. That the 

 fishes are negative to neutral water is thus confirmed. To 

 ascertain the chemical reaction of the water at the point in the 

 tank where the fishes turned back from the neutral end, numerous 

 samples were titrated from this region, during the experiment. 

 They showed that the water at this point contained about I c.c. 

 of CC>2 per liter. The graphs shown in Chart 1. are typical for 

 all. 



