584 
Journal o f Agricultural Research 
Vol. XXX, No. a 
xanthophyll bleaches with access of 
air and also very quickly in the dark, 
much more quickly than carotin. It 
is not stated whether the carotin was 
dissolved in ether or alcohol, hence the 
results may not be comparable. 
Observations made have shown that 
the ether solutions have bleached, 
while petroleum ether and especially 
alcohol solutions of pure xanthophyll 
and pure carotin are apparently stable, 
as has been shown in this paper. 
After several weeks the petroleum ether 
solution of xanthophyll is only slightly 
bleached. 
RELATIVE OXIDATION OF PURE CAROTIN 
AND PURE XANTHOPHYLL 
Ewart states that pure samples of 
carotin oxidize more easily than do 
those of pure xanthophyll. Aqueous 
emulsions of carotin oxidize more 
rapidly than do those of xanthophyll. 
Goerrig finds that at high temperature 
xanthophyll in drying leaves is more 
sensitive to oxidation than carotin. 
At room temperature the reverse is true 
in sunlight. The writer has shown 
that an ether solution of carotin is 
more stable at temperatures of from 
about 10 to 20° C. than is a solution 
of xanthophyll. An ether solution of 
carotin is less stable in the sunlight 
than is a solution of xanthophyll. 
Carotin in the dry form at room tem¬ 
perature in the light (not direct sun¬ 
light) and in the dark is less readily 
oxidized than is xanthophyll. 
In general, it is evident that carotin, 
in solution or as the pure substance, is 
more stable than xanthophyll in the 
dark and more unstable in the light. 
Goerrig found that carotin was 
affected more than xanthophyll when 
drying leaves were exposed to sun¬ 
light. This investigation shows that 
similar conditions exist in the case of 
pure carotin and pure xanthophyll 
pigments when they are in ether 
solution and exposed to sunlight. 
Ewart has stated that carotin emulsions 
bleach more readily than those of 
xanthophyll in sunlight. 
Attention should be called to the 
fact that the colorimetric and the 
spectrophotometric readings given 
above for carotin (Table VIII) do not 
confirm the following statement made 
by Palmer and Eckles (6): “ Spectro¬ 
scopic bands apparently disappear 
long before the pigment shows signs 
of bleaching.” In this case the two 
methods of observation in the work 
reported here should give far different 
values (Table VIII) for the amount of 
carotin present, and the spectro¬ 
photometer would give a lower figure. 
The results in this paper check as 
closely as could be expected, and so 
the conclusion is drawn from the work 
presented that both the spectroscopic 
and the colorimetric properties of a 
carotin or a xanthophyll solution vary 
directly with the pigment content of 
that solution, which means that the 
spectroscopic bands disappear only 
as the solutions show colorimetric 
signs of bleaching. 
SUMMARY 
Apparent inconsistencies regarding 
the behavior of xanthophyll are pointed 
out in the literature on the yellow 
pigments. 
The isolation and purification of 
xanthophyll is fully outlined and de¬ 
tails of preparation are given. 
At 25° C. 9.5 mgm. of xanthophyll 
dissolve in 1 liter of petroleum ether 
(B. P. 50 to 55° C.), 201.5 mgm. 
dissolve in 1 liter of absolute ethyl 
alcohol, 134.9 mgm. in 1 liter of abso¬ 
lute methyl alcohol, and 952 mgm., 
in 1 liter of pure anhydrous ether. 
Xanthophyll is unstable in ether 
solutions, is very stable in absolute 
ethyl alcohol, and is slightly unstable 
in petroleum ether when kept in the 
ice box. Carotin is unstable in ether 
solutions but apparently is perfectly 
stable in alcohol and petroleum ether. 
In the dry state xanthophyll oxi¬ 
dizes more readily than carotin. In 
solution xanthophyll oxidizes more 
readily than carotin when kept in the 
ice box, but when the solutions are 
kept in the sunlight at room tempera¬ 
ture carotin oxidizes more rapidly 
than xanthophyll. These results are 
in harmony with those of Goerrig on 
the oxidation of pigments in drying 
leaves. 
LITERATURE CITED 
(1) Clover, A. M. 
1922. THE AUTOXIDATION OF ETHYL ETHER. 
Jour. Amer. Chem. Soc. 44: 1107-1118. 
(2) Ewart, A. J. 
1918. ON CHLOROPHYLL, CAROTIN AND XAN¬ 
THOPHYLL AND THE PRODUCTION OF SUGAR 
FROM FORMALDEHYDE. PrOC. Roy. SOC. 
Victoria 30: 178-2C9. 
(3) Gill, A. II. 
1918. THE OCCURRENCE OF CAROTIN IN OILS 
and vegetables. Jour. Indus, and Engin. 
Chem. 10: 612-614. 
(4) Goerrig, E. 
1918. VERGLEICHENDE UNTERSUCHUNGEN 
Uber den carotin-und XANTHOPHYLL- 
GEHALT GRt)NER UND HERBSTLICH GELBER 
blatter. Bot. Centbl., Beihefte. (I) 
35: 342-394. 
