EXTRACTION OF CHLOROPHYLL 239 



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 u{j in 

 a mill and shaken in a bottle with i "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 0"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 

 mixture is shaken for 5 minutes and a further quantity of i 

 litre of 80 per cent acetone is now added. The liquid is 

 filtered off on a pump and the residue treated three times with 

 half a litre of 80 per cent acetone. The total filtrate should 

 measure 37 litres and contain 47 grams chlorophyll. 



In order to ascertain what proportion of the total chloro- 

 phyll present has been removed in any particular extraction, 

 another quantity of dried material, say from 100 to 200 grams, 

 may be subjected to an exhaustive percolation with an excess 

 of alcohol until the alcohol comes through colourless. Both 

 extracts are then diluted until i kg. of dry powder corresponds 

 to 200 litres of extract and their strengths are compared by 

 means of a colorimeter. 



Similarly, a fairly accurate estimate of the amount of 

 chlorophyll present in a solution can be made by colorimetric 

 comparison with a solution containing "025 gram of pure 

 crystallized chlorophyll dissolved in i litre of alcohol. For 

 this purpose the yellow colouring matters must, however, be 

 removed ; this is done by allowing the solution to stand for 

 some time with alcoholic potash ; the solution is then decanted 

 from the brown resinous deposit which settles on the sides of 

 the vessel, and, after washing the latter with a little more 

 alcohol, the combined alcoholic solutions are diluted with 

 water and extracted with ether to remove the yellow colouring 

 matters. 



After suitably diluting with alcohol, the solution is then 



