REACTION AND RESISTANCE OF FISHES. 24! 



of copper have been especially large, however, for small blue-gills 

 lived in both kinds as well as in tap-water, so long as the water 

 was slightly acid. 



A comparison of the conductivities of the two kinds of water 

 showed that the once-distilled had a conductivity 1 of 600 X io~ r 

 while the conductivity of the twice-distilled was only 10 X io~ 7 . 

 These conductivities are for 25 C. The conductivity of the 

 water probably does not indicate the amount of copper present 

 however for the metal is in all likelihood present in the col- 

 loidal state. Mengarini and Scala ('12) have shown that a num- 

 ber of metals, including copper, form a colloidal solution with 

 distilled water even at room temperature, and especially in 

 the absence of air. The conditions in a still would be especially 

 favorable for the reaction, since the temperature is high and 

 air excluded. 



The addition of an acid to a colloidal solution would tend to 

 precipitate the colloid, and this undoubtedly explains in part 

 the effect of addition of acid in making distilled water less 

 toxic, 2 as it will be shown that it does. Since, however, it has 

 been shown (Bullot, '04) that distilled water which contains 

 no copper is still toxic to organisms, other factors must be con- 

 cerned. The evidence of the experiments presented in the present 

 paper, indicates that the neutrality of the water is one of these 

 factors. 



It has been suggested in the preceding pages that the blue- 

 gills and crappies differ in respect to the hydrogen ion concen- 

 tration which they select and their resistance to the distilled 

 water bears out this point as the crappies die in it in a day or 

 so, while the blue-gills live indefinitely. 



(i) Experiments with Once-distilled Water. This water was 

 slightly acid to phenolphthalein and was neutral to methyl 

 orange. Its toxicity was tested by placing fishes in jars 

 containing a liter of the water. A 1 2-gram crappie died in this 



1 The conductivity of pure water is I X io~ 7 . 



2 Locke ('95) calls attention to the fact that poisonous distilled water may 

 lose its poisonous properties (if due to copper) by long boiling, and especially when 

 brought into contact with sulphur, carbon, manganic oxide, cotton wool, silk, 

 and other substances. The effect is very probably again due to the precipitation 

 of the colloidal copper. 



