EESPIEATION 



121 



another jar, c, which is partially filled with baryta water. 

 The final outlet from c can be attached to an aspirator 

 by which a stream of air can be drawn through the 

 apparatus. 



Before the incoming air reaches the jar A it is made to 

 pass through another jar, r, containing a solution of caustic 

 potash which frees it from all traces of carbon dioxide. 

 To ascertain that this is secured, it passes next through a 

 jar B which contains baryta water. A stream of air is 

 then passed slowly and continuously through the whole 

 apparatus, and as it bubbles through the baryta water in c 



FIG. 83. APPARATUS TO SHOW THE EXHALATION OF CARBON DIOXIDE BY 

 G-ERMINATING SEEDS. THE AIR ENTERS THROUGH THE TUBE ON THE LEFT ; 



ITS CARBON DIOXIDE IS ABSORBED BY THE POTASH IN F. IT PASSES THROUGH 

 A, IN WHICH THE SEEDS ARE PLACED, AND THE CARBON DIOXIDE GENERATED 

 THERE IS CARRIED OVER INTO C, WHERE IT IS PRECIPITATED BY THE BARYTA 

 WATER. 



it causes the formation of a white precipitate, which 

 analysis shows to be barium carbonate. The formation 

 of this body proves the evolution of carbon dioxide from 

 the seeds, as the entering air contains none. By using a 

 known strength of baryta water in c, the amount of the 

 gas evolved in a definite time may easily be ascertained. 



These two processes, the absorption of oxygen and the 

 exhalation of carbon dioxide, are characteristic of what is 

 known as respiration. As already stated, it is a normal 

 process of the life of almost all protoplasm, and is con- 

 tinually going on so long as life lasts, although it is not 

 easily observed while the converse process, the absorption 



