220 STUDIES IN ADVANCED PHYSIOLOGY. 







self increased quantities, and in that condition is forced into 

 bottles which are then tightly sealed, in order to retain the 

 gas at the original pressure. A bottle of mineral water that 

 had been filled from a tank subjected to a carbon dioxide 

 pressure twice as great as that of a second tank would have 

 twice as much carbon dioxide gas in it as a similar bottle 

 filled from the second tank. 



The water of our wells and streams is, of course, in 

 contact with the air, and the air presses on it with a pres- 

 sure equal to fifteen pounds to the square inch. In conform- 

 ity to the law just given certain and definite amounts of air 

 are dissolved or absorbed by the water. Thus the oxygen 

 which is absorbed in ordinary river water and which serves 

 for the respiration of fishes is accounted for in this way. 

 Dalton's law might be stated in another way which may 

 help to make this matter clearer. Liquids absorb gases un- 

 til the pressure of the gas dissolved in the liquid is just the 

 same as the pressure of that gas above the liquid. A few 

 illustrations may prove helpful. If, in the case of an ordi- 

 nary engine boiler a valve be opened in the lower part of 

 the boiler where the water is, the water is forced out with 

 the same pressure as the steam would be forced out from the 

 upper part of the boiler. That is to say, the pressure in the 

 water of the boiler is the same as the pressure of the steam 

 above that water. Or, to illustrate further, in a bottle not 

 quite filled with some heavily charged mineral water there is 

 a certain amount of gas above the liquid. If the stopper 

 from such a bottle should be removed not only would the gas 

 above the liquid be forced out, but the gas dissolved in the 

 liquid would try to relieve itself of the pressure to which it 

 has been subjected, and so flow out of the bottle, frequently 

 carrying bits of the liquid along with it as a froth or foam. 

 As soon as a glass of heavily charged soda-water is drawn 

 and placed on the table to be served, the (CO 2 ) gas which 

 was dissolved in the water, now being relieved of the pres- 

 sure of the gas above it, leaves the water and causes the 

 familiar froth, or, as it is called, the effervescence of that 



