46 



AERATION AND AIR-CONTENT. 



dioxid. The amount of oxygen in distilled water when saturated 

 varies from 9.7 c.c. per liter at 0° C. to 7.77 c.c. at 10° C, 6.28 c.c. 

 at 20° C, and 5.43 c.c. at 30° C. Hence the amount of oxygen in 

 water varies from about 9 c.c. in midwinter to 6 c.c. in midsummer. 

 Ponds and reservoirs in Massachusetts often showed 100 per cent 

 of saturation at the surface and at 10 and even 20 feet, ranging usually 

 to zero at 40 to 50 feet. River-water in Ohio ranged for the most 

 part from about 80 to 100 per cent, and under conditions of super- 

 saturation up to 169 per cent. Tap- water varied from 54 to 100 

 per cent, averaging about 85 per cent in surface-water suppHes and 

 from 9 to 100 per cent, averaging 61 per cent, in driven-well waters. 

 The amount of free carbon dioxid in rain-water varied from 1.8 to 

 29 parts per million, with an average of about 7 parts. Streams 

 showed 2 to 19 parts, with an average of 7 parts, and shallow ponds 

 in summer, 3 parts. A reservoir gave 2 to 3 parts at 1 foot, 4 to 11 

 at 24 to 26 feet, and 16 at 46 feet, while a lake yielded 2 parts at 1 

 foot, 2.25 at 10 feet, 9 at 25 feet, 1*1 at 40 feet, and 17 at 50 feet. 

 Volk (1906 : 13) found the amounts of oxygen in the Elbe River 

 shown in table 12 during the autumn of 1904 and 1905. 



Table 12. 



Hesselmann (1910 : 117) has made an exhaustive study of the 

 oxygen-content of various bog and water habitats in Sweden. The 

 oxygen-content of the water in slowly growing pine forest was 2.49 

 to 6.08 c.c. per hter, and in spruce moors and swamps, 0.25 to 3.73 

 c.c, with higher amounts only exceptional. In streams and lakes 

 the amount varied from 5.17 to 7.61 c.c, and in springs and brooks 



