CHLOROPHYLL AND THE CHLOROPLASTS 355 



stances. There was, first of all, the problem of obtaining pure prepara- 

 tions of chlorophyll. For a long time investigators could not even come 

 to an agreement as to what elements are contained in the chlorophyll 

 molecule ; thus it was held by some that besides carbon, hydrogen, oxygen, 

 nitrogen and magnesium, chlorophyll also contained iron and phosphorus. 

 It has, however now been quite definitely established that the last two ele- 

 ments are not components of the chlorophyll molecule. The methods 

 •for extracting chlorophyll, freeing it from other substances and making 

 pure chlorophyll preparations have been carefully worked out, largely 

 through the efforts of Willstatter and his collaborators. Besides the 

 difficulties associated with freeing the pigments from other substances in 

 the process of extraction and purification, the property characteristic of 

 most leaf pigments, namely, that of great instability, must be dealt with. 

 It must be realized that the oxygen of the air, certain enzymes and Hght, 

 all cause decomposition to take place and that the substances thus formed 

 interfere with procuring pure preparations. 



The method of determining the constitution, which has been followed 

 with considerable success in the investigation of highly complex sub- 

 stances, is that of breaking up the large molecule into a number of 

 smaller ones. These splitting products are often crystalline substances 

 of known composition and structure, which can be purified and identified 

 by means of well established methods. This general method of analysis 

 has been followed with many fatty substances, carbohydrates and proteins 

 of plant and animal origin. A study of the chemical nature of the 

 simpler splitting products and the establishing of their constitution are 

 of much help in determining the constitution of the original complex 

 substance and, in some cases, have made possible the synthesis of the 

 latter from the simpler compounds. The general method of breaking 

 up a complex molecule into simpler ones has also been utilized in the 

 study of the leaf pigments. Many extensive investigations have been 

 carried out by this method, notably by Hoppe-Seyler,^^ Fremy,^« Gau- 

 tier,^^ Tschirch,*° Marchlewski ^^ and Hartley.*' At the present time most 

 of these investigations have little more than an historical interest. In 

 the hands of Willstatter and his collaborators the results of previous 

 investigators were greatly extended, many of the contradictory results 

 were clarified, errors were discovered and their cause determined; in 

 brief, out of a generally chaotic condition, order was established. The 

 complex molecular structure of many of the splitting products of chloro- 

 phyll was determined as well as the manner in which the different groups 

 are bound together. This has constituted a great advance toward the final 



'^ Hoppe-Seyler, Zeit. physioI. Chcm., 3, 339 (1879) ; 4. 193 (1880) ; 5, 75 (1881). 

 ^Fremy, Compt. rend., 50, 405 (1860); 61, 188 (1865); 84, 983 (1877); Ann. 

 chim. phys. (4), 7, 78 (1866). 



^"Gautier, Compt. rend., 89, 861 (1879). 

 'Tschirch, Ber. bot. Gcs., 5, 128 (1887). 



Marchlewski, "Die Chemie des Chlorophylls," Braunschweig, 1909. 

 'Hartley, Jour. Chem. Soc. 59, 106 (1891); 85, 1607 (1904). 



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