176 WATER CULTURE, PHOTOSYNTHESIS, RESPIRATION. 



ment in which the arrangements are the same, but leave 

 the jar open to admit air, and omit the potash. 



(/) Fit a wide-mouthed glass jar with a cork cut in two 

 across the middle. Smear with vaseline and wax the 

 edges of the two half-corks ; pour some caustic potash or 

 clear baryta- water into the bottle. Lay the bottle on its 

 side and place between the halves of the cork a starch- 

 free Primrose leaf, so that part of the leaf is inside the 

 bottle and the rest outside (Fig. 40). Cover the ap- 

 paratus with a large bell-glass, and set it in a good light. 



After some hours 

 remove the leaf, de- 

 colorise it and test 

 with iodine. If care 

 has been taken in 

 fitting up the ap- 

 paratus, the part of 

 the leaf that was 

 inside the bottle (in 

 air free from carbon 

 dioxide, which the 

 baryta - water ab- 

 sorbs readily) con- 

 tains no starch, while the part outside does. This is often 

 termed " Moll's experiment." 



Instead of the jar and split cork, we may use two similar 

 glass dishes with ground edges, placing some baryta- water 

 or potash in the lower dish, smearing the edges of both 

 dishes with vaseline or wax, and inverting the empty dish 

 over the other one, so that the leaf is held between the 

 edges of the two dishes. 



233. Gas Analysis. In experiments on photosyn- 

 thesis carbon dioxide may be tested for, or absorbed 

 from the air or the gases to be analysed, by means of 

 (1) caustic potash, (2) soda-lime, (3) baryta- water, (4) 

 lime-water. Oxygen is readily absorbed by (1) pyro- 

 gailate of potash ; and its presence may be tested for 

 by (2) its power of causing a glowing splinter to burst 

 into name, (3) its causing de-oxygenated and therefore 



Fig. 40. Moll's Experiment. 



