324 PIGMENTS 



In this connection the formula assigned to aetiophylHn 

 (p. 318) should be compared. 



In the course of attempts to synthesize chlorophyll Tronow 

 and Popow * have prepared compounds, having the structures 



R R R R 



and find that where R is either CH3 — or CgHs — the compounds 

 exhibit typical reactions of aetioporphyrin whose constitutional 

 formula is given on page 319. 



EXTRACTION OF CHLOROPHYLL. 



The usual method of extracting chlorophyll from green 

 tissues consists in first steeping the fresh material in hot water 

 to destroy oxidizing enzymes and then extracting the colour- 

 ing matter by means of warm alcohol. Willstatter, however, 

 recommends the use of dried in place of fresh material, and 

 extracting by shaking with organic solvents (ethyl or methyl 

 alcohol, ether or acetone) in the cold. 



The chief advantage in using dried material lies in the 

 fact of its relatively small bulk, 100 grams of stinging nettle 

 leaves, for example, weighing only 25 grams after drying. It 

 has been shown, moreover, that the operation of drying pro- 

 duces no change of any importance in the chlorophyll, since 

 the results obtained from dried material have been repeated 

 and confirmed on fresh material. 



On the other hand, organic solvents containing an appreci- 

 able amount of water are preferable to the dry solvents. This 

 is attributed by Willstatter to the fact that aqueous solvents 

 dissolve out salts, such as potassium nitrate, from the cell sap, 

 and these affect the state f of the colloidal solution of chloro- 

 phyll in the chloroplast, thereby rendering the chlorophyll 

 more easily accessible to the solvent. Moreover, the number 

 of substances going into solution is thereby increased, and the 



* Tronow and Popow : " J. Russian Chem. Soc," 1927, 59, 327. 

 % See section on Colloids. 



