S 
546 REPORT OF THE COMMISSIONER OF FISHERIES. 
tributes a very small part to the total atmospheric bulk, is extremely 
soluble. 
Ignoring its minor constituents and regarding the argon group of 
gases with the nitrogen, the atmosphere is approximately made up of 
79 parts of nitrogen gas and 21 parts of oxygen gas by volume. The 
carbon dioxid present has no particular connection with the gas dis- 
ease and will not be referred to further. When water is exposed to 
the atmosphere it absorbs these two gases until a state of equilibrium 
is reached, when no further change takes place and these gases, if the 
temperature and pressure remain constant, are neither further absorbed 
nor given off by the water. The latter is then said to be saturated 
with air. If now any change takes place in the temperature of the 
water, or in the pressure which it sustains, either a further absorption 
will occur or some of the air will be given off from the water. These 
changes, especially under artificial conditions, may oecur rapidly, and 
the adjustment to an equilibrium may not keep pace; therefore, at 
at any given time water may fall short of saturation and air be pass- 
ing into it, or it may be supersaturated and air be passing away from 
it, assuming of course in either case that it is not protected from con- 
tact with the atmosphere. In other words, water may hold in solution 
an excess ora deficiency of air, or an excess or deficiency of either 
one of the air gases, nitrogen or oxygen, independently of the other. 
The rapidity with which water supersaturated or infrasaturated with 
air will become saturated, or in equilibrium, will depend upon the 
urea of its contact with the atmosphere. It therefore follows that 
water only moderately exposed to the atmosphere, as in tanks or most 
containers, may remain for a considerable time either above or below 
the saturation point. But the tendency is constantly toward the 
equilibrium of the saturation point, which will always finally be 
reached. 
The actual amounts of nitrogen and of oxygen which water will 
absorb from the atmosphere have been determined by analyses of air- 
saturated water. Authorities differ somewhat in the results. The 
figures cited here and in the tables give the highest values. One liter 
of pure water at 0° C., the freezing point, and at a pressure of 760 
mm. of mercury, the standard atmospheric pressure, will absorb 19.53 
c. c. of nitrogen from the atmosphere (Pettersson and Sonden) and 
10.18 c. c. of oxygen (Winkler); at 20° C. and 760 mm., 12.8 ©. ¢. 
nitrogen (Dittmar), and 6.35 c. c. of oxygen (Winkler). Pure sea 
water takes up somewhat less. These figures are taken from Comey’s 
Dictionary of Solubilities. 
RESPIRATORY PROCESSES AND MECHANISM IN FISHES. 
To understand the effect of supersaturated water upon fishes it is 
necessary to consider the respiratory processes and the mechanism by 
