584 
bulletin oe the bureau of fisheries. 
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A 
Pig. 14. — Dissolved gases, Canandaigua Lake, Aug. 20, 1910. 
For explanation see fig. 9, p. 580. 
in Keuka Lake, i6.8 cc., while in the 
other lakes it varied from 21.0 to 24.0 cc. 
In Conesus and Otisco Lakes there was an 
appreciable increase of this gas toward 
the bottom; in the former the bottom 
water contained 5.1 cc. more than the 
surface and in the latter 7.3 cc. 
A much greater range in the quantity 
of fixed carbon dioxide has been found 
in the waters of the Wisconsin lakes. 
In them the amount varies from a mini- 
mum of i.o cc. to a maximum of about 
50.0 cc. 
Half-hound carbon dioxide . — In neutral 
waters and in those which possess free 
carbon dioxide the half-bound carbon 
dioxide is assumed to be equal in amount 
to the fixed. But in waters which give 
an alkaline reaction with phenolphtha- 
lein there is an excess of fixed carbon 
dioxide which equals in amount the de- 
ficiency of the half-bound. From a bio- 
logical standpoint the half-bound carbon 
dioxide is of very great importance since 
it serves as a source of carbon dioxide 
for the photosynthetic activities of chlo- 
rophyllous organisms. From four-fifths 
to five-sixths of it may be consumed in 
this process, but none of the fixed car- 
bon dioxide is available. The free car- 
bon dioxide may be consumed by the 
algae, but if found at all in the upper 
water it is present very generally in rela- 
tively small amounts. 
Free carbon dioxide . — There are four 
sources of free carbon dioxide in lake 
waters. They are the atmosphere, de- 
composition of organic material, the 
respiration of organisms, and spring or 
ground waters. This gas constitutes a 
small portion of the atmosphere, from 
three to four parts per 10,000, so that 
where a water is freely exposed to the 
