230 MORRIS M. WELLS. 



but not to OH ion. It therefore gives an acid reaction with 

 CO 2 but is unaffected by the minute amount of OH ion which 

 is present in solutions of bicarbonates. 1 Methyl orange will 

 give an alkaline reaction in water in which the concentration 

 of H ion is considerably greater than that of OH ion. Thus, 

 in the presence of CO 2 , titration with this indicator is not a 

 determination of true alkalinity for the water is as a matter 

 of fact acid, since it contains a higher concentration of H than 

 OH ions. Marsh ('07) makes this error when he states (p. 337) 

 that "the reaction of water which will support fish life must be 

 slightly alkaline." His determinations were made with sulfuric 

 acid, using methyl orange as indicator. The water to which he 

 refers ("Potomac service water") was in all probability acid to 

 phenolphthalein. Marsh also states that "when the water 

 becomes even slightly acid, fishes cannot live in it." This 

 would mean that fishes can not live in water which has been 

 made slightly acid to methyl orange by the addition of an acid. 

 I have added sulfuric acid to tap water until it gave an acid 

 reaction to methyl orange, and find that fishes live in it as well 

 as in the original tap water, i. e., normally. The fishes should 

 not be placed in such water until some little time after the adding 

 of the sulfuric acid, however, for in the process of changing the 

 carbonates to sulfates, a large amount of carbonic acid is liberated 

 (CaCO 3 + H 2 SO 4 5 CaSO 4 + H 2 CO 3 ) and until this carbonic 

 acid has dissociated and the CO 2 passed off into the atmosphere 

 to a large degree, its presence will kill fishes which may be in- 

 troduced. The amount of carbonic acid formed will depend 

 upon the amount of carbonates in the water. (The reaction 

 with bicarbonates will give the same result.) 



In the following pages I shall introduce experimental data to 

 show that fresh water fishes cannot live normally in water that 

 is alkaline but that they require a certain degree of acidity to 

 carry on their normal activities. 



1 Noyes ('13) gives a table (p. 388) showing the acidity or alkalinity of solutions 

 at the change of color for various indicators. Methyl orange gives an alkaline 

 reaction when the OH concentration is only io~ 9 while phenolphthalein is not 

 affected until the concentration of OH ion reaches io~ 5 . Methyl orange gives an 

 acid reaction when the H ion concentration is io~ 4 while phenolphthalein reacts 

 when the H ion concentration is only a little more than io~ 8 . 



