174 CAROTINOIDS AND RELATED PIGMENTS 



in Chapter III that Kiihne (1878) had previously decided, partly on 

 spectroscopic grounds, that the egg yolk pigment could not be identi- 

 cal with the so-called lutein in the corpus luteum. It remained, 

 however, for Willstattcr and Escher to attempt the isolation of the 

 pigment in sufficient quantity for chemical analysis. This proved to 

 be a rather difficult task and involved working with large quantities 

 of material. Starting with the yolks of 6,000 eggs, which weighed 

 110 kg., only 4 grams of crude crystalline pigment was obtained. 

 The method of isolation will be described in Chapter VIII. 



The crude egg yolk pigment was purified first by repeated crystal- 

 lization from hot methyl alcohol. About 250 cc. of boiling alcohol 

 were required to dissolve 0.25 grams of the crude product, from which 

 approximately 0.16 grams of crystals came down on standing for 

 some hours. It is stated that it was also found possible to obtain 

 crystals showing a constant melting point by dissolving the crude 

 crystals in carbon disulfide and recrystallizing from this solvent. The 

 chemical studies on the purified substance showed the following aver- 

 age results. For comparison similar data are shown for the plant 

 xanthophyll isolated by Willstatter and Mieg (1907). 



Plant Egg yolk 

 xanthophyll xanthophyll 

 CH.OH of crystallization, calculated for 



CJHsnO-, CH,OH = per cent 5.33 5.33 



CH,OH found percent 4.76 4.35 



Molecular weight in CHCU. ebulloscopic 



method, calculated for C,oH M 2 568.4 568.4 



Molecular weight found 512. 640. 



Elementary analysis; percentage composition { C = 84.44 84.44 



required' for formula CH M 2 ? H = 9.93 9.93 



Elementary analysis found $ C = 84.22 83.58 



} H = 9.92 10.13 



Melting-point (corrected) 173.5 174.5 195 196C. 



An examination of these data shows that the plant xanthophyll 

 analyzed by Willstatter and Mieg showed excellent agreement, at 

 least in chemical composition, with the theoretical values. The re- 

 sults of the analyses of the egg yolk pigment, however, can only be 

 regarded as approximations, at best. The molecular weight deter- 

 mination is also very unsatisfactory. Willstatter and Escher explain 

 the low figure for the content of methyl alcohol of crystallization on 

 the grounds of a possible oxidation of the pigment during the process 

 of removal of the alcohol, which required a period of about 10 days 

 over phosphorus pentoxide. The explanation does not seem entirely 

 satisfactory, however, in view of the statement that this process took 



