580 
Journal o f Agricultural Research 
Vol. XXX, No. 6 
the volumes of the absolute ethyl 
alcohol, ether, and U. S. P. ether 
solutions were made up to 250 c. c. 
In the case of the petroleum ether 
solution it was necessary to bring the 
pigment into solution with 20 c. c. of 
absolute alcohol and then the volume 
was made up to 200 c. c. by the addi¬ 
tion of petroleum ether. These solu¬ 
tions of xanthophyll were then stored 
at a temperature of 10° to 20° C. and 
determinations, both colorimetric and 
spectrophotometric, were made on the 
solutions. The data are given in 
Table VI. 
The solutions were made up on 
March 31 and were kept in the ice box, 
except for short periods when the 
no oxidation during the time that they 
were in storage. 
The keeping quality of carotin in the 
various solvents was quite similar to 
that of xanthophyll. In other words, 
carotin and xanthophyll rapidly oxidize 
when kept in ether solutions, while both 
carotinoids are stable when kept in a 
cool, dark place either in petroleum 
ether or in absolute alcohol, absolute 
alcohol apparently being the medium 
in which both pigments are most stable. 
OXIDATION OF XANTHOPHYLL AND 
CAROTIN 
The rate of oxidation of xanthophyll 
has been variously reported in the 
Table VI .—Keeping qualities of xanthophyll in solution 
Solvent 
Date 
Colorimetric data 
Spectrophotometric 
data 
Colorimeter readini 
in mm. using Lovib 
' f " 1,1 j 
5 10 
! 
?s, depth 
ond slides 
20 
Colori¬ 
meter 
determin¬ 
ations, 
solution 
undi¬ 
luted, 
mgm. per 
liter, 
average 
results 
Trans- 
mittancy 
after solu¬ 
tions 
were di¬ 
luted 5 
times 
Spectro¬ 
photom¬ 
eter de¬ 
termina¬ 
tions, 
mgm. per 
liter 
Absolute alcohol_ 
Apr. 
8 
3.4 
5.3 
9.2 
7.53 
0.202 
8.30 
Ether __ ____ 
_ do. 
3.3 
5.6 
9.3 
7.44 
.212 
8.00 
U. S. P. ether ... 
...do_ 
3.0 
5.2 
9.0 
7. 96 
. 190 
8.60 
Petroleum ether _ 
..do.... 
2.6 
4.1 
7.1 
9.66 
.148 
9.90 
Absolute alcohol-:- 
Apr. 
24 
3.2 
5.5 
8.9 
7. 73 
. 198 
8.28 
Ether __ 
...do. 
4.3 
7.1 
12.5 
5.83 
.277 
6.65 
U. S. P. ether _ 
...do. 
3.8 
6.2 
10.7 
6.63 
.222 
7. 75 
Petroleum ether _ 
do_ 
2.7 
4.2 
7.2 
9.40 
.146 
10.00 
Absolute alcohol- 
May 
24 
3.1 
5. 0 
7.7 
8.40 
.210 
8.12 
Ether _ _ 
...do 
7.8 
12.3 
17.1 
3.63 
.457 
4.08 
U. S. P. ether_ 
...do_ 
5. 7 
9.1 
14.5 
4. 53 
.359 
5. 30 
Petroleum ether.. 
...do_ 
3.0 
4.3 
7.6 
8.90 
.148 
9.85 
Absolute alcohol_ 
July 
21 
3.8 
5.4 
8.7 
7. 40 
.207 
8.16 
Ether _ _ _ 
...do. 
( a ) 
. 286 
1. 30 
U. S. P. ether 
__do_ 
(•) 
* .292 
1 . 26 
Petroleum ether _ 
do_ 
3.2 
5.1 
9.6 
7. 86 
. 173 
9.10 
Absolute alcohol- 
Sept. 
11 
3.4 
5.3 
9.2 
7. 53 
.214 
7.96 
Petroleum ether_ 
...do. 
3.5 
5.7 
9.6 
7. 23 
.205 
8.20 
a Too dilute to estimate. 
determinations were being made. 
Table VI and Figure 1 show clearly that 
xanthophyll oxidizes quite rapidly in 
ether solutions, the decomposition being 
about the same whether the ether was 
freshly distilled or not. 
The oxidation of the carotinoids in 
ether agrees well with the develop¬ 
ment of ethyl peroxide (G 2 H 5 ) 2 0 3 in 
ether as described by Clover (I). 
There probably is a correlation between 
the development of peroxide and the 
oxidation of the carotinoids. 
Petroleum ether and absolute alcohol 
solutions kept well, showing practically 
b Undiluted. 
literature. This is also true of carotin. 
The oxidation of the pure pigments will 
be discussed first and then the oxidation 
of the impure pigments, that is, those 
that are still present in the leaf tissue. 
The melting point of the pigments 
is lowered when the carotinoids oxidize. 
On account of this fact it was attempted 
to ascertain the comparative rate of 
oxidation of the two yellow pigments 
by determining their melting points 
at various intervals of time when the 
powders were exposed to the air at 
room temperature. The results were 
entirely unsatisfactory, for pure xan- 
