103 now CROPS FKED. 



keep pace with each otLer until all the absorhable air is 

 removed from the gaseous mixture, and condensed or fixed 

 in tlie al)Sorbent. 



In tliis manner, a portion of the atmosphere enclosed in 

 a large glass vessel may be perfectly freed from watery 

 vapor and carbonic acid by a small fragment of caustic 

 potash. By standing over sulphuric acid, ammonia is 

 taken from it ; a piece of phosphorus will in a few hours 

 absorb all its oxygen, and an ignited mass of the rare 

 met.il titanium will remove its nitrogen. 



Osmose of Gases. — By this expression is understood the 

 passage of gaseous bodies through membranes whose 

 pores are too small to be discoverable by optical rneanSy 

 such as the imperforate wall of the vegetable cell, the 

 green cuticle of the plant whore not interrupted by stomata^ 

 vegetable parchment, India rubber, and animal membranes, 

 like bladder and similar visceral integuments. 



If a bottle filled with air have a thin sheet of India 

 rubber, or a })iece of moist bladder tied over its mouth 

 and then be placed within a bell of hydrogen, evidence is 

 at once had that gases penetrate the membrane, for it 

 swells outwards, and may even burst by the pressure of 

 the hydrogen that rapidly accumulates in the bottle. 



Gaseous Osmose is DiiTusion llodified by the Influence 

 of the Membrane. — The rapidity of osmose * is of coursa 

 influenced by the thickness of tlie membrane, and the 

 character of its pores. An adhesion between the mem- 

 brane and the gases would necessarily increase their rate 

 of penetration. In case the membrane should attract or 

 haA e adhesion for one gas and not for another, complete 

 separation of the two might be accomplished, and in pro- 

 portion to the difference existing between two gases as re- 

 gards adhesion for a given membrane, would be the de- 

 gree to which such gases would be separated from each 



' The osmose of liquids is discussed in detail in "How Crops Grow," p. 854. 



