346 EEPOKT OF THE COMMISSIONER OF FISHERIES. 



tributes a veiy .small part to the total atmospheric balk, is extremely 

 soluble. 



Ignoring its minor constituents and regarding the argon group of 

 gases with the nitrogen, the atmosphere is approximately made up of 

 70 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 

 Avater, or in the pressure which it sustains, either a further absorption 

 will occur or some of the air will be given oft' from the water. These 

 changes, especiall3^ under artificial conditions, may occur 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 ma}" hold in solution 

 an excess or a dcticieuc}'^^ of air, or an excess or deficiency of either 

 one of the air gases, nitrogen or oxj^gen, independently of the other. 

 The rapidity with vv^hich water supersaturated or infrasaturated with 

 air will become saturated, or in equilibrium, will depend upon the 

 area of its contact with the atmosphere. It therefore follows that 

 water onl}- 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 

 equili1)rium of the saturation point, which will alwa3's 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 c. c. 

 nitrogen (Dittmar), and 6.35 c. c. of oxygen (Winkler). Pure sea 

 water takes up somewhat less. These figures are taken from Come3''9 

 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 



