386 
BULLETIN OF BUREAU OF FISHERIES 
From the field studies on specific conductance it was found advisable in pollution 
studies to look for specific pollutant action if the conductivity of the water exceeded 
1.000 mho in all types of streams except those draining the more alkaline regions, or 
2.000 mho in the case of the western streams discussed above, for the specific conduct- 
ance is very readily raised by acid and salt pollutions of several sorts. 
Specific conductance, therefore, offers a ready method for detection of salt and 
acid pollution, as produced by water from oil wells, by wastes from industries using 
salts or strong acids, and by soluble salts of heavy metals. This method was used 
very satisfactorily by the writer in determining the extent of downstream pollution 
from lead and zinc mines in the Coeur d’Alene district in Idaho (Ellis, 1932), and in 
following pollution by acid mine waters from coal mines in Tennessee and West 
Virginia. 
Carbon Dioxide 
Determinations of free, half-bound and fixed carbon dioxide were made by the 
methods of Seyler as described by Kemmerer, Bovard, and Boorman (1923) and 
American Public Health Association (1933). The data are expressed as cubic centi- 
meters of carbon dioxide per liter. 
FIXED CARBON DIOXIDE (CHIEFLY CALCIUM AND MAGNESIUM CARBONATES) 
In figures 16 and 17 the data from 6,770 determinations of fixed carbon dioxide 
in flowing streams of the United States and southern Canada collected during the 
warm season, June to September, inclusive, 1930-35, are presented. The extreme 
range of fixed carbonates varied from almost 0 to 70 cubic centimeters per liter, with 
40 cubic centimeters per liter as the usual upper limit. A composite of determinations 
from waters where good fish faunae were thriving (fig. 16 A) covered the entire range 
from 0 to 70 cubic centimeters per liter. In this composite 96 percent of the 2,190 
analyses showed the stream water to carry less than 50 cubic centimeters per liter of 
fixed carbon dioxide and 53 percent lay between 10 and 30 cubic centimeters per liter. 
Comparing these findings with the classification of lake water given by Birge and 
Juday (1911), it may be seen that most of the flowing waters fell in the second class, 
designated as medium waters; and that the large percent of the river and stream 
waters could be classified as either soft or medium. Hard waters were distinctly in 
the minority. 
Reviewing this composite in connection with the findings on fixed carbonates in 
the waters of the various river systems, it is evident that between 10 and 40 cubic 
centimeters of fixed carbon dioxide may be expected in most of the fresh-water streams 
of the United States. Fixed carbon dioxide in itself, however, does not seem to be a 
determining factor in classifying flowing waters as suitable or unsuitable for fresh- 
water fishes. Various limnologists have pointed out the importance of fixed car- 
bonates in maintaining food supply, and, therefore, fish faunae of various lakes 
(Welch, 1935), but from the data on rivers and streams presented here it must be 
concluded that either carbonates are not limiting factors or that they are always 
present in sufficient quantities to meet the needs of the stream biota. An exception 
to this last statement, however, must be taken at least in the case of fresh-water mus- 
sels, as carbonates do constitute a very vital limiting factor for these animals. 
