192 WATER CULTURE; PHOTOSYNTHESIS, RESPIRATION. 



bell-jar is covered with a black cloth, the liquid in (a) soon becomes 

 turbid and milky. 



Fig. 44. The Arrows show the direction of the Current of Air, which is drawn 

 through by attaching an " Aspirator" at the left of the Apparatus. The two 

 pieces of glass tubing fitted with stop-cocks may be dispensed with and clips 

 used on the rubber tubing (shown black). 



In Fig. 44 the plant used is covered with 

 a bell-jar standing on a glass plate, its rim 

 being smeared with plasticine and vaseline 

 to make the junction air-tight. 



252. Respirometer. Almost any of 

 the respiroscopes described may be used as 

 respirometers, for qualitative analysis of 

 the gases exchanged in respiration. The 

 tube leading from the chamber should dip 

 into mercury (for rough purposes water 

 may be used, though it will of course ab- 

 sorb the gases especially carbon dioxide 

 to some extent) ; allowance must be made 

 for the volume occupied by the seeds ; the 

 volumes of gas absorbed by the reagents 

 (potash solution and pyrogallate solution) 

 must be measured with corrections for tem- 

 perature, etc. 



In using Ganong's Respirometer (Fig. 45), 

 supplied by the Bausch and Lomb Optical 

 Company, ten Oats or Barley grains are 

 germinated till the roots are visible (2 to 

 4 mm. long), their volume is found by im- 

 mersion in water in a small glass measure, 

 and they are put in the oval chamber which 

 has a water-bulb for a measured small volume of water to keep the 

 seedlings moist. The seeds and water placed in the chamber 



Fig. 45. Ganong's Repiro 

 meter. 



