236 PIGMENTS 



the results obtained from dried material have been repeated 

 and confirmed on fresh material. 



On the other hand, organic solvents containing an appreci- 

 able amount of water are preferable to the dry solvents. This 

 is attributed by Willstatter to the fact that aqueous solvents 

 dissolve out salts, such as potassium nitrate, from the cell sap, 

 and these affect the state * of the colloidal solution of chloro- 

 phyll in the chloroplast, thereby rendering the chlorophyll 

 more easily accessible to the solvent. Moreover, the number 

 of substances going into solution is thereby increased, and the 

 solution is no longer effected by the solvent alone but by the 

 solvent together with the accessory substances. 



If dry solvents are used, the extract is much less pure since 

 it contains a larger proportion of carotinoids, lecithins, etc., 

 whose solubilities are very similar to those of chlorophyll. 



The following methods of extracting dried or fresh leaves 

 respectively are described by Willstatter : 



1. Half a kilo of dried material is spread on a porcelain 

 Buchner funnel in a layer of not more than 4 to 5 cms. thick, 

 and I '5 litres of solvent are drawn through this layer by means 

 of a filter pump in the course of half an hour. This filtrate, 

 measuring about 0*9 litre, contains from 4 '2 5 to 4*5 grams of 

 chlorophyll. 



The solvent employed may be either 90 per cent (aqueous) 

 alcohol or 80 per cent (aqueous) acetone. The former filters 

 rather more rapidly, but acetone has the advantage over 

 alcohol in preventing the chlorophyll from undergoing what 

 is known as allomerization, a peculiar change which interferes 

 with its power of crystallization, and prevents it giving the 

 phase test. 



2. Two and a half kilos of fresh leaves are ground up in 

 a mill and shaken in a bottle with 1*5 litres of acetone to 

 remove water and mucilage and to stop enzyme action. The 

 acetone is then filtered off on a pump ; it contains no chloro- 

 phyll. The residue is then freed from acetone by filtering on 

 a pump under a pressure of 200 atmospheres, and the resulting 

 hard mass, weighing O'8 kg., is broken up and ground again. 

 On adding I '5 litres of acetone the latter becomes diluted to 

 80 per cent by the water still remaining in the residue ; the 



*See section on Colloids, p. 283. 



