326 PIGMENTS 



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 

 crystalhzed 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 

 compared in a colorimeter with the standard chlorophyll 

 solution. 



In this way it was found that I kg. of fresh stinging 

 nettle leaves containing 25-6 per cent of total solid contained 

 an amount of chlorophyll equivalent to i-6 grams of the 

 crystalline substance, corresponding, therefore, to 1-6 X 1-38 

 = 2-2 grams of amorphous chlorophyll.* 



The following simple experiments are selected from a 

 number described by Willstatter and Stoll t to illustrate the 

 properties of chlorophyll and the carotinoids : — 



1. Grind up 10 grams of fresh stinging nettle leaves with 

 silver sand in a mortar. Cover with 20 c.c. acetone and filter 

 over a pump ; wash the residue with more acetone and filter 

 again ; the filtrate will contain 0-02 gram chlorophyll. 



2. Dried powdered leaves do not part with their colour 

 on treatment with benzene or light petroleum, and only yield 

 chlorophyll very slowly to anhydrous alcohol, acetone, or 

 ether, but may be readily extracted by means of 90 per cent 



* The factor 1-38 for converting crystalline into amorphous chlorophyll 

 represents the ratio between the molecular weights of these two substances. 



t Willstatter and Stoll : " Untersuchungen uber Chlorophyll," Berlin, 

 1913. 



