106 CHEMISTRY. 



bles as they pass upward. So, also, if water be boiled, the 

 air that is dissolved in it escapes, being expanded by the 

 heat, and rising with the steam. 



134. Composition of the Air that is in Water. The ail- 

 that is dissolved in water is not of the same composition 

 with the atmosphere. The ingredients are the same, but 

 the proportions are different. There is a larger proportion 

 of oxygen in the air that is in water. The reason is that 

 oxygen is more soluble in water than nitrogen, and there- 

 fore water absorbs or dissolves more of the former from the 

 air than it does of the latter. Here is a marked and ob- 

 vious provision of Providence for the benefit of the inhab- 

 itants of the waters. As fishes and other animals that live 

 in the water get so little air compared with animals that 

 live out of the water, it is necessary that the air they breathe 

 should have a larger proportion of that ingredient which is 

 essential to the purposes of life. 



135. Experiment with Snow. What we have just stated 

 furnishes the explanation of an experiment which was for- 

 merly a great puzzle to philosophers. The experiment is 

 this : Let a glass bottle be filled with snow, and, corking it 

 tightly, let the snow melt. You will, of course, have in the 

 bottle water and the air which escaped from the snow as it 

 melted. On examining this air it will be found to contain 

 much less oxygen than common air does; and yet the air 

 which was in the interstices of the snow was common air 

 which became mingled with it as it fell. The question is, 

 what has become of the missing oxygen. The answer is 

 easy. A part of the air in the snow has been dissolved in 

 the water; but since water dissolves a larger proportionate 

 quantity of the oxygen of the air than of its nitrogen, the 

 air which is not dissolved will contain a larger proportion 

 of nitrogen. 



1 36. Oxygen Supplied to Fishes by Water-Plants. Fishes 



