The Extraction of Pure Pigments from the Leaf. 19 



Willstatter first dried his leaves and powdered them bel'ore 

 extracting the pi>«ment. The advantages and disadvantages of 

 using fresh and dried leaves may be summarised as follows. 

 Preparations from fresh leaves are important (i) for analytical 

 purposes when small quantities only are necessary ; (ii) when it 

 is necessary to find the true proportions of the various pigments ; 

 (iii) when the action of chlorophyllase on chlorophyll is utilised for 

 the preparation of crystalline chlorophyll. On the other hand 

 fresh leaves have the disadvantages that (i) they are more diiBcult 

 to divide finely ; (ii) it is more difficult to prevent the alteration of 

 the chlorophyll in fresh leaves than in the dry powder. However, 

 this difficulty may be overcome by treating with a watery solution 

 of methyl or ethyl alcohol of such concentration that no chlorophyll 

 is extracted while at the same time the enzymes are destroyed. 



Willstatter himself used the dried powder of leaves for all 

 ordinary extractions. The use of the dried powder has these 

 advantages, (i) To obtain the same quantity of pigment a much 

 smaller quantity of material is required than if fresh material is 

 used. This allows of the use of smaller vessels for the extraction 

 operations, a very important advantage when the small quantity of 

 chlorophyll present in the crude material is considered, (ii) A 

 saving in the solvents is effected. These are not diluted by the 

 water content of the leaves which constitutes about 75% of the 

 fresh leaves, (iii) As a leaf can be chosen the dried powder of 

 which keeps well, the preparation of the pigments can be made 

 independent of the season and growing place of the plants. 



The disadvantages of using the dried material are as follows : 

 (i) Loss of chlorophyll owing to drying. If the drying is done 

 properly this loss is very small. Thus Willstatter found in alcoholic 

 extracts of dried nettle and of Galeopsis 95 to 96% of the chlorophyll 

 in fresh leaves, (ii) Again, if the leaves are not properly dried, 

 alteration of the pigments may take place. Some dried leaves are 

 spoilt by being kept (e.g., Grass), others (e.g., Elder and Conifer 

 leaves) are even spoilt by drying. But even in such cases the 

 chlorophyll may be preserved unchanged if the leaves are dried in 

 a vacuum desiccator over sulphuric acid. 



It should be mentioned that Willstatter has compared the 

 pigments extracted from fresh leaves and dried leaf powder and 

 has found them identical. 



(3) The Solvents. For the various reasons given above 

 Willstatter used the dried powder of nettle leaves for all ordinary 



