21] STUDY OF SOUTHERN WISCONSIN FISHES— CAHN 21 



Still another problem that assumes an important role in the life history 

 of various fish is the hydrogen ion concentration of the water. Insofar as 

 the lakes are concerned, the range of variation is not great within the 

 county, all of the lakes investigated being alkaline from the surface to the 

 bottom. This is in spite of the acid condition of much of the spring water 

 which forms one of the main sources of water supply to the lakes. Through- 

 out the summer of 1923 a total of 634 hydrogen ion concentration deter- 

 minations were made by the colorimetric method in the various lakes, at 

 different depths, day and night. During the first ten days of February, 

 1924, a series of 160 readings was made to determine the winter conditions 

 in respect to the ionic concentration. In collecting the samples of water for 

 the determinations, a special apparatus designed by Shelford (1923) was 

 used, consisting of a specially designed pump with two-way pet cocks, by 

 means of which a vacuum is established within a small test tube and a 

 sample of water drawn in without contact with air. Into this tube the two 

 drops of indicator were injected through a rubber membrane by means of 

 a hypodermic outfit, and the concentration read and compared with the 

 standard series of tubes. A long rubber hose with a hole diameter of 1 mm. 

 was used in bringing up the sample, and for bottom work a pan designed 

 for the purpose of confining a local area of water assured the sample being 

 of the region desired. 



The results of the field work show that there is a definite relation 

 between oxygen content of the water and the H-ion concentration, which 

 may be stated: 1) As the oxygen content of the water decreases, the H-ion 

 concentration increases. 2) While ordinarily there is an increase in CO2 

 accompanying a decrease in O, the H-ion concentration seems to bear 

 very little if any relation to the C0 2 changes: that is, changes in O are 

 regularly accompanied by changes in the H-ion concentration in the 

 opposite direction, while changes in the C0 2 content either may or may 

 not be accompanied by a change in the H-ion concentration. 



The following table, 3, gives a partial summary of a part of the data: 



