A UMNOLOGICAIy STUDY OP THE FINGER LAKES. 
583 
CARBON DIOXIDE. 
Carbon dioxide is readily soluble in water, but the total amount that may be found 
in a lake water depends chiefly upon the quantity of other substances present with which 
it is most generally combined. It exists in three different states. A part of it is in 
close chemical union with substances that are dissolved in the water, more especially 
calcium and magnesium, forming the carbonates of these substances. This is known 
as the fixed carbon dioxide. Another is in a 
fairly loose combination with the carbonates, 
converting them into bicarbonates. This con- 
stitutes the half -bound carbon dioxide. A third 
portion exists in an uncombined or free state, 
and is known as the free carbon dioxide. 
Fixed carbon dioxide . — ^The quantity of fixed 
as well as of half -bound carbon dioxide depends 
upon the amount of calcium and magnesium 
that may be present in the water, and the 
amount of these substances, in turn, is dependent 
upon their relative abundance in the drainage 
basin. The normal carbonates of calcium and 
magnesium are only slightly soluble in pure 
water. Rainwater absorbs carbon dioxide from 
the air, and obtains still more from decomposing 
organic matter when it reaches the earth. When 
this water, which is charged with more or less 
free carbon dioxide, comes into contact with 
these normal carbonates, they are freely con- 
verted into bicarbonates, which readily pass into 
solution. Thus, if the water which falls upon 
the adjacent land and reaches the lake either 
by surface drainage or by percolating through 
the ground and finally emerging as a spring, 
comes into contact with an abundance of calcium 
and magnesium carbonates on its journey, the 
lake water will possess a relatively large amount Fig. 13.— Dissolved gases, Keuka Lake, Aug. 18, 1910. 
of bicarbonates, and it will be classed as “ hard ” explanation see fig. 9, p. 580. 
water. If, however, the inflowing water comes into contact with very small amounts 
of these normal carbonates, the quantity of bicarbonates will be small, hence the lake 
water will be “soft.” 
This serves to explain why there is such a marked difference in the quantity of fixed 
carbon dioxide in the waters of the Finger Lakes. It varied from a minimum of 6.8 cc. 
per liter of water in Canadice Lake to 24.0 cc. in Canandaigua Lake. (See table xviii, 
p. 602, and fig. 9-18.) In Hemlock Lake the fixed carbon dioxide amounted to 12.9 cc.. 
