240 PIGMENTS 



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 i •6 x 1-38 

 = 2'2 grams of amorphous chlorophyll.* 



The following simple experiments are selected from a 

 number described by Willstatter and Stoll f 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 

 alcohol or 80 per cent acetone yielding a green solution with 

 a strong red fluorescence. 



3. Prepare an ethereal solution of chlorophyll as follows : 

 About 15 c.c. of an 80 per cent acetone extract of dried leaves 

 are poured into 30 c.c. of ether contained in a tap funnel and 

 mixed with 50 c.c. water. The ethereal solution rises to the 

 surface. It should be washed four times with 50 c.c. of water 

 each time by carefully allowing the water to run down the 

 side of the funnel without shaking. If a 30 per cent methyl 

 alcoholic solution of potash is now run under the ether layer 

 a brown colour is produced at the junction of the two liquids. 

 The colour gradually changes to olive-green and finally back 

 to the original green. The reaction, which is known as the 

 " Phase Test," is due to the saponification of the chlorophyll 

 with formation of the potassium salt of chlorophyllin. Conse- 

 quently on dilution with water the green colour remains in 

 the aqueous layer and is no longer soluble in ether. 



4. Shake vigorously 5 c.c. of an ethereal solution of chloro- 

 phyll (prepared as above) with 2 c.c. of concentrated methyl 



*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 iiber Chlorophyll," Berlin, 1913. 



