388 
Pond VII contained chub-suckers, golden shiner, bullhead, and mud 
minnow. No bare breeding-bottom. Pond VII, E, is much older than 
VII, W. 
Pond XIV contained black bullheads. No bare breeding-bottom. 
A few observations were made on pH at bottom under certain types 
of vegetation: Under white water-lilies, 6.9-7.2; under yellow water- 
lilies, 7.7-7.9; under duckweed and smartweed, 6.8-7.3. 
GENERAL RELATIONS OF HyprRoGEN Ion CONCENTRATION 
TO OTHER FACTORS . 
1. Relations of pH to dissolved oxygen.—There are nearly always ; 
correlations between CO, content and dissolved oxygen, at least with a 
fairly constant ‘alkalinity.” A fairly constant alkalinity exists in the sea. 
Relative to the sea, McClendon (’17a) states that “in so far as the sea 
is a closed system O, varies inversely with CO,, due to the action of 
organisms, the possible error being 30 percent.” He presents a chart 
showing the amount of oxygen to be expected in sea water of various 
“alkalinities,’ etc. Bélow the thermocline a lake in summer is a closed 
system, and in so far as alkalinity remains constant there is an inverse 
relation of O, and CO,, which is, however, by no means constant. In 
some cases the sum of O, and CO, in c.c. per liter is a constant, but the 
relation is always an inverse one. This stability of the O, and CO, values 
probably depends upon circulation, diffusion, changes in alkalinity, etc., 
but in all the work described herein there is a direct relation between 
pH and O, (cf. Table VII and Table VI). When hydrogen ions content 
decreased, as indicated by higher pH figures, oxygen increased. 
2. Relations of pH to carbon dioxid and “alkalinity” —In waters 
of about the same alkalinity the amount of free CO, is as good an index 
of its suitability for fishes as hydrogen ions (Shelford and Allee, ’10). 
The amount of CO, means nothing, however, unless alkalinity be meas- | 
ured. The work of Greenfield and Baker (’20) shows that the HT 
ions may be calculated. The equation is 
4 CO, X 10-7 , 
H+ = Be i a (es 
(HCO,— ) a 
when CO, is expressed in p.p.m. and bicarbonate as p.p.m. CaCO, 
but when both bicarbonate and free CO, are expressed in c.c. per liter* 
the equation is 
35 xX 10z NEO; A 
(H+) =—_____—_— + 1 10-8 
GICOR) 
“To check the accuracy of these calculations, several samples of 
water, from a variety of sources and varying widely in mineral and : 
organic content, were examined. Bicarbonate and free carbon dioxide 
* Total must be used, i. e. bound and half-bound. P 
