ly] CHLOROPHYLL 29 



solution in the solvents in which it is soluble, i.e. ethyl alcohol, acetone, 

 chloroform, ether, carbon bisulphide, pyridine and benzene. Chlorophyll 

 b, when isolated, is a green-black solid giving a pure green solution : it 

 has much the same solubilities as chlorophyll a. The two chlorophylls, 

 however, can be separated by their different solubilities in methyl alcohol. 

 Both can be obtained in microscopic crystals. 



Carotin crystallizes in orange-red crystals, and xanthophyll in yellow 

 crystals. 



In the chloroplastids these pigments occur mixed with various colour- 

 less substances, fats, waxes, and salts of fatty acids. 



When chlorophyll is spoken of, it will be understood to refer to the 

 green pigments and not to the yellow. 



The pure pigments, when isolated, are readily soluble in acetone, ether 

 and benzene. When very thoroughly dried nettle leaves are treated with 

 pure acetone, no green colour is extracted, but if a few drops of water 

 are added, the extract becomes green. Also if acetone is poured on to 

 fresh leaves, the pigment is extracted. The explanation offered for these 

 phenomena is that chlorophyll is present in a colloidal condition in the 

 cell. This point will be considered again later (see p. 36). 



The Common Nettle ( Urtica) is the plant which has been used for 

 material for the extraction of chlorophyll on a large scale, and it also 

 forms very useful material for extraction on a small scale. The pigment 

 has been found to be unaltered by drying, and, since dried leaves involve 

 far less bulk and dilution of solvents, material should be dried before 

 using. Some leaves (Elder and Conifers) are spoilt by drying. From 

 dried leaves pure solvents, such as petrol ether, benzene and acetone, 

 extract very little pigment for reasons which will be mentioned later, 

 but if the solvents contain a moderate amount of water, the pigment is 

 readily soluble. About 80 7o acetone is the best solvent. The nettle 

 leaves are removed from the stalks and laid on sheets of paper to dry. 

 When well air-dried they are finely powdered, and the powder further 

 dried at 30-40° C. in an incubator. The leaf-powder can be kept for a 

 considerable time in a well- stoppered bottle. 



Expt. 19. Extraction of pigment. Two grams of leaf-powder are sucked to a filter- 

 paper on a small porcelain funnel and 2-3 c.c. of 85 % acetone are added. This is 

 allowed to soak into the powder for a few minutes. The fluid is then sucked through 

 with the pump, the flask disconnected and more acetone added. The operation is 

 repeated until 20 c.c. of the solvent have been added, when the powder is sucked dry. 

 A deep blue-green solution with a red fluorescence is obtained which contains all the 

 four pigments from the leaf. The acetone extract thus obtained is then poured into 

 double the quantity of petrol ether contained in a separating funnel. An equal 



