CHLOROPHYLL AND THE CHLOROPLASTS 357 



pounds ; the magnesium is not electrolytically dissociated in solution and 

 does not give the usual ionic reactions for this metal. The group con- 

 taining the magnesium is very stable toward alkalies, so much so, that 

 the carboxyl groups in the molecule can be split oflf without affecting 

 the magnesium linkages. This property enabled the fact to be established 

 that magnesium was actually present, as well as the nature of the union 

 of this metal with other groups in the molecule. By successive breaking 

 down of the chlorophyllin molecule, finally by heating to 240^ vi^ith alco- 

 holic alkali, a series of beautifully colored and fluorescent crystalline 

 compounds was obtained with, one, two and three carboxyl groups, the 

 phyllins. These compounds, which have been given names descriptive 

 of their color as glaucophyllin and rhodophyllin, and of which at least a 

 dozen have been prepared are carboxylic acids containing magnesium, as 

 e.g. (MgN4C3iH33)COOH, pyrrophyllin and (MgN4C3iH32) (COOH), 

 glaucophyllin. The removal of the last carboxyl group yields aetiophyllin, 

 C3iH34N4Mg, giving an ash containing 8 per cent of magnesium oxide. 



All phyllins contain four nitrogen atoms to one atom of magnesium. 

 The oxygen atoms are not bound to magnesium and are not a part of 

 the metal complex ; only the nitrogen atoms are combined to the metal. 

 Based upon Werner's conceptions of partial valences, of the structure 

 of metal derivatives of acid imides, biuret and dicyandiamidine, Willstat- 

 ter concluded that in aetiophyllin nitrogen is united to magnesium by pri- 

 mary and partial valences. The nitrogen is part of a pyrrol ring, so that 

 the magnesium nucleus would have the following structure : 



When treated with acids, phyllins break down with the loss of mag- 

 nesium, forming mono- and polycarboxylic acids. These acids also have 

 basic properties. The compounds thus formed are called porphorins 

 and take the prefix of the phyllins from which they were obtained, e.g. 



cyanophyllin, C3iH32N4Mg(COOH)2 > cyanoporphyrin, C31H34N4- 



(COOH)o, glaucophyllin > glaucoporphyrin, isomeric with cyanopor- 

 phyrin, and phyllophyllin, CaiHsA^MgfCOOH) > phylloporphyrin 



C3iH35N4(COOH). 



