228 PIGMENTS 



c.c. of water, lOOO c.c. of methyl alcohol in 200 c.c. of water, 

 and 1000 c.c. of methyl alcohol in 100 c.c. of water; it may 

 be finally freed from alcohol by careful agitation with water, 

 drying with fused sodium sulphate and evaporating, without 

 heating, in a vacuum. 



The residue so obtained is a waxy solid which dissolves in 

 neutral solvents to give solutions with a bluish-green colour 

 and red fluorescence. It is not possible to free the chloro- 

 phyll from carotin by this method. 



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 

 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 r6 grams of the 

 crystalline substance, corresponding, therefore, to i '6 x 1-38 

 = 2-2 grams of amorphous chlorophyll.* 



This particular sample of leaves, therefore, contained about 



* The factor i'38 for converting crystalline into amorphous chlorophyll 

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



