220 THE LIFE OF THE PLANT 



basin.^ A glass jar is placed in the middle of the basin ; 

 through the cork of the jar the tube of a glass funnel 

 is passed right down to the bottom, and also another 

 tube twice bent. An acid is poured into the jar, while 

 a ball of marble or chalk is placed in the funnel. Let 

 us see what happens to the apparatus when it is her- 

 metically covered by the bell A. There is air under the 

 bell ; therefore there is also oxygen. This oxygen will 

 be absorbed by the liquid in the basin ; as a result 

 the volume of air (a) under the bell will decrease ; the 

 pressure of air under the bell will diminish ; and, if it 

 diminishes, the small volume of air (b) contained in 

 the jar, above the acid, will begin to expand, and, 

 pressing upon the acid, will oblige it to rise in the tube 

 and to appear in the funnel (i.e. the level of the acid in the 

 beginning at m will be now at n, fig. 64, B). But here 

 it will meet the ball of marble or chalk, and will oblige 

 it to give off its carbonic acid.^ This carbonic acid 

 will replace the oxygen absorbed, and will go on being 

 given off until the former pressure is established under 

 the bell A ; then the air in the jar (b) will fall back to 

 its original volume ; the acid at the same time will go 

 down from a again to m, and everything settle down 

 until the liquid in the glass basin, after having absorbed 

 a fresh quantity of oxygen, upsets the balance again 

 between the air under the bell (a) and the air of the 

 jar (6). Was I not right in calling this apparatus an 

 artificial animal ? It breathes ; it absorbs oxygen and 

 gives off carbonic acid, and almost in the same quantities. 

 The plant is placed on a tripod in the upper part of 

 the bell ; it will use the carbonic acid given off by the 

 apparatus, and will itself in its turn give off oxygen, 



' In order to absorb oxygen in presence of carbonic acid Saussure's well- 

 known mixture can be used consisting of iron filings, flowers of sulphur, 

 and water ; as well as a solution of cuprous chloride (Cu CI) and kitchen 

 salt, or a solution of chromous chloride (Cr Cl^). Phosphorus (dangerous 

 in summer) may also be used. 



' See chapter iii. 



