Simple Laboratory Experiments on Leaf Pigments. 2,7 



If an alcoholic solution of sulphur is poured into a large volume of 

 distilled water, a sulphur sol is produced. 



Experiment 17. To show the difference between a true and a 

 colloidal solution of chlorophyll. 



Evaporate 10 c.c. of the acetone extract to complete dryness 

 and test its solubility in ether, petrol ether and benzene. Now add 

 these solvents to some of the colloidal solution prepared in the last 

 experiment, and note that the chlorophyll does not dissolve in any 

 of these solvents. If, however, some salt solution, e.g., a little 

 magnesium sulphate be added, the chlorophyll is precipitated from 

 its colloidal state and is now soluble in ether and other solvents. 



Experiment 18. To show that chlorophyll in the plant is 

 probably in the colloidal condition.^ 



Some nettle powder is carefully dried, e.g., by keeping it at 

 sec. to 40''C. in an oven, and then further drying in a vacuum 

 desiccator over sulphuric acid. Small quantities of this dry powder 

 are put in test-tubes and different pure water-free substances such 

 as acetone, ether, benzene and absolute alcohol are added. Note 

 that these solvents are not coloured by the chlorophyll. It can be 

 demonstrated that the extracted pigment is easily soluble in any of 

 these substances. 



Repeat the experiment with nettle powder moistened with a 

 few drops of water, and note that the solvents are immediately 

 coloured. 



Experiment 19. Pure solvents are able to extract chlorophyll 

 from fresh leaves. 



Crush 10 grams of fresh leaves of nettle, horse-chestnut or 

 elder in a mortar with some clean sand, and put the crushed 

 material on a filter paper in a Buchner funnel. Add 20 c.c. pure 

 acetone and suck it through by means of a water pump. Repeat 

 this several times. The pure solvent is here able to extract the 

 pigment. 



It can also be observed that the leaf substance after 

 extraction is brown, owing to the action of oxydases on the leaf. 

 If therefore, the leaves are dipped first in boiling water, these 

 oxydases are destroyed, and the leaf substance after extraction 

 remains colourless. 



Experiment 20. Treatment of fresh leaves with boiling water 



changes the condition of the chlorophyll. 



1 Although Willstatter regards the facts upon which this experiment is 

 based as a proof of the colloidal condition of chlorophyll in the loaf, in the 

 writers' opinion such a simple explanation will not cover the facts. 



