390 
BULLETIN OF BUREAU OF FISHERIES 
IRON 
Iron determinations were made by the method of American Public Health Asso- 
ciation (1933), using permanent standards of cobalt and platinum salts. 
A limited number of total iron determinations were made in typical localities for 
correlation with studies of water from abandoned coal mines. Eighty-three deter- 
minations of total iron in waters of Mississippi, Missouri, Ohio, Tennessee, Atlantic 
coast, and Gulf coast systems gave the following grouping: 
Figure 18. — Free carbon dioxide values (as cubic centimeters of carbon dioxide per liter, bottom line) for the waters of various 
river units. Stippled and black graphs composed as explained under figure 6. 
At stations where good fish faunae were found (75 cases) the free iron ranged from 
a trace to 30 p. p. m., with 69 of these 75 cases below 10 p. p. m. In streams polluted 
with either mine waters or chemical effluents carrying iron compounds the total 
iron ran much higher, the maximum found in this series being 202 p. p. m. in waters of a 
stream of high acidity (pH 4.4) flowing from a coal mine in operation near Turley, 
Tenn. Iron in quantities above 100 p. p. m. was associated with acidity above average 
and when such conditions were found chemical or mine pollutions were suspected. 
In the experimental tests (see section on heavy metals) it was found that 100 
p. p. m. of total iron were not immediately harmful to either fish or daplmia; and that 
such quantities, unless a constant flow were maintained, were usually diminished 
during the first few davs of experimental tests as a result of precipitation so that the 
