228 MORRIS M. WELLS. 



usual and that their sensitivity seemed to be lessened, as they 

 would swim into factors to which they are normally very nega- 

 tive. It was at this point that the study of the effects of acidity, 

 etc., was decided upon. 



Tests showed that the water entering the aquaria was practi- 

 cally neutral to phenolphthalein, varying a little from day to 

 day. To determine the effect of the neutral water upon the 

 fishes, a number was taken from the aquaria and placed in tubs 

 of partially aerated tap water (water contained 6-10 c.c. COa 

 per 1.). After a day or so in this water, they began to behave 

 normally in the gradient again. The flow of water into the 

 aquaria was now modified by diminishing the amount of aeration. 

 The tap water was run down a wooden trough 12 ft. long, into 

 the aquaria. This saturated it with oxygen but left it decidedly 

 acid with CO 2 . From now on the mortality of the stock of 

 fishes was very low. The aquaria were not so crowded as at 

 first, but that the decrease in the number of fishes does not ex- 

 plain the low mortality, will be brought out in experiments to 

 be presented later. 



The importance of the chemical reaction of the water to fishes 

 had been foreseen (Wells, '13, p. 337) and it was decided that 

 the peculiar properties of the Illinois water offered an excellent 

 opportunity for continuing this investigation. At the same 

 time it was thought that the work might perhaps throw some 

 light upon a number of the reactions of fishes to salts, which 

 seemed difficult to explain. 



The advantages of the Illinois water are due to the following 

 chemical properties: As it flows from the tap it is acid to phenol- 

 phthalein from the excess (18 c.c. per liter) of COo, and alkaline 

 to methyl orange because it contains a large quantity (101 c.c. 

 per liter) of bicarbonates in solution. The bicarbonates have 

 been formed from carbonates according to the equation CaCOa 

 + HoCOa t^ Ca(HCO 3 ) 2 and when carbonates are dissolved 

 under the influence of excess of carbonic acid they are practically 

 all converted into bicarbonate, the quantity of unconverted 

 carbonate being negligible (Stieglitz, '09, p. 246, Seyler, '94, p. 

 105). Under the pressure in the water pipes, there exists an 

 equilibrium between the carbonic acid and the bicarbonates, 



