38 GAS EVOLVED. [CH. II 



passing cloud causing an alteration in the rate of assimi- 

 lation. For this reason it is better to use artificial light. 



(45) Chloroform 1 . 



Repeat experiment 41 and add a small quantity 

 (10 p.c.) of chloroform- water, that is, of water in which not 

 more than 1 per cent, of chloroform has been shaken. If 

 the experiment is cautiously performed it should be 

 possible to seriously diminish the rate of gas-discharge 

 without killing the plant. 



(46) Coloured light 2 . 



Proceed as in experiment 41, and when constant 

 readings are obtained, cover the beaker with a double 

 bell-jar containing ammoniacal copper- sulphate solution 

 and note the result. Sunlight must be employed as the 

 source of light. After an interval of 4 or 5 minutes, 

 when the readings should be approaching constancy, 

 replace the blue jar by another containing potassium 

 bichromate solution, and take a series of readings. It 

 will probably be necessary to alternate the blue and 

 orange light several times before a trustworthy result 

 is obtained, otherwise it is impossible to make sure of 

 avoiding the effect of slight variations in the intensity of 

 the light. 



(47) Collection of the gas. 



Place a quantity of any of the above-named water- 

 plants in a glass jar of about 12 14 cm. diameter. 



1 Bonnier and Mangin, Ann. Sc. Nat. 1880. 



2 Sachs' Botan. Zeitung. 1864. 



