238 MORRIS M. WELLS. 



raised to .02 N, but even now the avoidance of the alkali end was 

 not nearly so definite as in the experiments with the other alkalies. 

 Graphs 4 and 5 (Chart II.) show this indefinite reaction very 

 clearly. In the .02 TV gradient, the fishes were soon overcome 

 by the toxicity of the water, which they selected, and they died 

 there if not removed. 



The fact that fishes fail to recognize ammonia in solution is of 

 considerable importance, for this substance is being introduced 

 into fish waters in many kinds of sewage. Furthermore it will 

 be shown in the second paper of this series, that the gas 

 has not lost its toxicity even when it has been converted into 

 its various salts. The chemical explanation of the failure of 

 the fishes to recognize and react to the presence of fatal concen- 

 trations of the hydrate in solution is probably due to the fact 

 that the concentration of ammonia as gas, reaches a fatal con- 

 centration before the concentration of OH ion stimulates the 

 fishes sufficiently to cause them to react negatively. They do 

 not appear to react to the gas itself. Noyes ('13, pp. 203-4) 

 states that ammonia dissolves in water, in part, without chemical 

 change and that it is probable that a large part of the ammonia 

 exists, as such, in the solution. He quotes Moore ('07) as cal- 

 culating that only 30-40 per cent, of the ammonia exists as am- 

 monium hydroxide, NH 4 OH, at 20 C. Noyes thinks that the 

 per cent, may be even less than this. 



Again, the solution of ammonia diffuses through the water 

 with great rapidity; much more rapidly than do most other 

 substances. To determine the rate of diffusion, a little phe- 

 nolphthalein was added to the aspirator bottle (AB, Fig. i) 

 containing the ammonia solution. The pink solution could be 

 seen as it moved through the tank, and in less than a minute 

 it had spread over the entire surface, and to a lesser extent, had 

 penetrated the deeper water. Because of this rapid diffusion, 

 no perfect gradient could be established with this substance. 

 It may also be noted that ammonia behaves just opposite from 

 the salts, the latter spreading along the bottom. In the am- 

 monia experiments, the fishes seldom approach the surface, 

 while in strong carbon dioxide gradients, they spend much time 

 gulping the surface film. Shelford and Alice ('13, p. 231) state 



