Mar. 15, 1925 
Physical and Chemical Properties of Xanthophyll 
581 
thophyll is obtained in a very finely 
precipitated form, whereas carotin is 
in the form of crystals. To begin with, 
then, the substances are not in the 
same state of subdivision. Further¬ 
more, when carotin crystals are allowed 
to oxidize the outer portion of the crys¬ 
tal oxidizes first and, consequently, 
melts first in a melting point tube. 
There is a melting point (which appar¬ 
ently varies with the degree of oxida¬ 
tion) for the oxidized portion of the 
crystal, and there is also a melting 
point for the unoxidized portion. This 
was ascertained by viewing the melting 
point tubes, after heating so as to melt 
the outer surface of the crystals, under 
Of a solution (0.210 gm. per liter) 
of xanthophyll in pure redistilled ether, 
5 c. c. portions (each representing 1.05 
mgm. of xanthophyll) were placed in 
small crystallizing dishes. Half of 
these were kept in a dark box and the 
other half were placed upon the same 
box, where they were exposed only to 
subdued light. All were kept at room 
temperature and protected from dust. 
Each workday morning as long as the 
experiment was run 2 c. c. of ether for 
each sample was used to dissolve the 
pigments so as to reduce the effect of 
the protective action of the oxidized 
portion and also to dissolve the crys¬ 
tals which might form. The experi- 
Fig. 1 .—Spectrophotometric comparison of the rate of oxidation of xanthophyll in petroleum ether, 
alcohol, and ether when stored in the ice box at 10° to 20° C. 
the microscope. It is obvious that, 
such determinations made on the two 
pure pigments would be valueless in 
regard to comparative rates of oxida¬ 
tion. Pure xanthophyll is apparently 
more readily oxidizable than pure caro¬ 
tin, for all color disappears in the xan¬ 
thophyll sample before it does in the 
carotin sample, although this may per¬ 
haps be due to the fact that the sub¬ 
stances are in different states of sub¬ 
division. 
Two possible means of determining 
the relative rates of oxidation of the 
two pigments will now be considered. 
The first deals with the pigments in a 
dry state and the second with the pig¬ 
ments in solution. 
ment was begun on March 31, but no 
quantitative readings were made until 
April 8. The results of these tests on 
the rate of oxidation of the pigments 
are given in Table VII. Samples ex¬ 
posed to light showed a much greater 
rate of oxidation than those kept in 
the box at room temperature, pro¬ 
tected from light. After 36 days about 
25 per cent of the original amount of 
xanthophyll still remained in the sam¬ 
ple in the dark box, while only about 
1 per cent remained in the sample 
exposed to the light, as indicated by 
the spectrophotometric estimations. 
Experiments were conducted with 
carotin similar to those with xantho¬ 
phyll. The results are reported in 
