190 WATER CULTURE, PHOTOSYNTHESIS, RESPIRATION. 



251. Respiroscope Experiments. Various forms of 

 respiroscope may be put together easily from ordinary 

 laboratory apparatus. 



(a) To show that considerable volumes of carbon dioxide 

 are rapidly produced in the germination of seeds, half fill 

 a large glass jar with soaked Peas and fit the cork with a 

 twice bent tube leading into a narrow- necked bottle or 

 large test-tube containing lime- or baryta- water. Set in 

 a fairly warm place and note the copious white precipitate 

 (calcium or barium carbonate) produced by the escaping 

 carbon dioxide. As a control, place an equal volume of 

 the reagent in a second bottle or tube of the same size. 

 As a second control, set up a similar apparatus containing 

 soaked Peas which have been boiled ; to prevent the growth 

 of Bacteria, cover the killed Peas with 10 per cent, formalin. 



(6) Repeat the preceding experiment, but this time 

 lower into the jar a smaller jar or tube containing baryta- 

 water or caustic potash, and let the bent tube dip into 

 water coloured with red ink. As the reagent absorbs the 

 carbon dioxide produced, the coloured water rises in the 

 outside tube. 



(c) Fit a wide jar with a cork bored by two holes. 

 Cork the wide mouth of a thistle-tube, and push the tube 

 through one of the holes until it nearly reaches the bottom 

 of the jar. Through the other hole pass a short glass 

 tube connected by rubber tubing, carrying a clip, with a 

 J- shaped tube the short arm of which is drawn out in a 

 flame to a fine capillary point. On the bottom of the jar 

 place wet blotting-paper and some Peas or Wheat grains 

 that have been allowed to germinate until the roots are 

 about 1 cm. long. 



Then dip the J-tube to the bottom of a tall narrow jar 

 or large test-tube filled with lime- or baryta-water, and 

 clip the rubber tubing. After two or three days, loosen 

 the clip, uncork the thistle-tube and pour water into it so 

 as to drive the gas out of the jar through the J-tube, from 

 the fine opening of which it escapes into the reagent, 

 causing a precipitate. Set up a similar apparatus, but 

 without the seeds, as a control. 



