CH. l] RESPIRATION. 3 



mercury 1 in the beaker Hg. The flask contains enough 

 germinating barley to cover a piece of wet filter-paper 

 at the bottom of the flask. Barley germinates well in 

 winter : it should be soaked in water for 24 hours and 

 kept in damp air for 24 hours before use. A test-tube 

 T half full of strong KHO is introduced into the flask, 

 which is then closed by a sound tightly fitting rubber 

 cork. As the C0 2 , produced by respiration, is absorbed 

 by the KHO, the mercury in the beaker Hg is sucked 

 up the tube A. In starting the experiment it is necessary 

 to warm the air in the flask before the end of A is forced 

 into the mercury, so that as the air cools again the mer- 

 cury may be sucked a little way up the tube to a point 

 which will then serve as zero for subsequent observations. 

 The warming may be done by immersing the flask in 

 water at 40 for a few minutes ; or it may be warmed by 

 the hands. If the mercury fails to rise within 6 hours 

 the reason is probably to be found in the cork fitting 

 badly. For this reason it is perhaps advisable to run 

 melted wax-mixture* round the line of contact between 

 the cork and glass. 



(3) Sachs method 9 . 



Place 100 germinating peas in a jar, A, fig. 2, closed 

 by an india-rubber cork pierced by two holes and fitted 



1 Or the beaker Hg may be filled with water. 



2 Wax-mixture consists of resin 15 parts, bees-wax 35 parts, vaseline 

 50 parts. The wax and the vaseline are melted together, the resin is 

 powdered, gradually added and stirred. 



3 Physiologie (French Translation), 1863, p. 295, fig. 35. Also 

 Pfeffer's Physiologie, i. p. 349, fig. 38. 



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