578 
Journal of Agricultural Research 
Vol. XXX, No. 6 
precipitate (the depth of color depends 
upon several factors) forms almost 
immediately and can be collected on a 
hardened filter. The precipitate is 
washed quickly with pure low-boiling 
petroleum ether and dried in a vacuum 
desiccator at once. The drying is 
only for the purpose of removing the 
petroleum ether. The melting point 
should now be 173 to 174° C. 
Drying is accomplished in 15 to 20 
minutes, and weighings of xanthophyll 
are made at once for all of the solu¬ 
tions needed. Any xanthophyll re¬ 
maining may be stored in the ice box 
in a flask containing petroleum ether, 
methyl or ethyl alcohol. If more xan¬ 
thophyll is required later for any pur¬ 
pose the xanthophyll is recrystallized 
from methyl alcohol and is reprecipi¬ 
tated from chloroform and petroleum 
ether. In this way a pure product is 
assured each time. Pure anhydrous 
ether is the best solvent for xantho¬ 
phyll, but as deterioration is greatest 
in this solvent readings must be made 
at once. If xanthophyll is dissolved 
in absolute alcohol, difficulty is often 
experienced in getting the last traces 
of the pigment into solution. It 
would seem that pure xanthophyll 
might be obtained by precipitating 
several times from chloroform with 
petroleum ether, as is the case when 
carotin is purified by dissolving in 
carbon disulphide and then recrys¬ 
tallizing from petroleum ether. Ob¬ 
servations have shown, however, that 
xanthophyll can not be purified in 
this manner. To get the purest xan¬ 
thophyll preparations, spectrophotom¬ 
eter readings show that crystalliza¬ 
tions must first be made from methyl 
alcohol and that the xanthophyll must 
then be precipitated from chloroform 
by the addition of petroleum ether. 
Melting-point determinations are not 
as good a criterion of purity as are 
spectrophotometric observations, as 
data given in a former paper ( 8 ) show. 
CHEMICAL AND PHYSICAL PROP¬ 
ERTIES OF XANTHOPHYLL 
SOLUBILITY 
Solubility determinations were made, 
using petroleum ether which fraction¬ 
ates at 50 to 55° C., absolute ethyl 
alcohol (99.7 to 100 per cent), absolute 
methyl alcohol, and anhydrous ether 
which had been specially prepared by 
washing U. S. P. ether with water four 
times, distilling over calcium chloride 
and then allowing to stand over sodium 
for a week, finally distilling immedi¬ 
ately before use. 
The xanthophyll used here was pre¬ 
pared fresh in every case as described 
in the preceding section. Solubility 
tests were made in a water bath kept 
at 25° C. and the pigment content 
was determined by means of the spec¬ 
trophotometer and the mercury line 
435.8 mu. The stability of xantho¬ 
phyll in absolute ethyl alcohol, in ab¬ 
solute ether, in U. S. P. ether, and in 
petroleum ether was also tested in this 
manner, since the results obtained in 
quantitative work depend upon the 
stability of xanthophyll in solution. 
The solubility of xanthophyll differs 
considerably from that of carotin, and 
this property is utilized in the separa¬ 
tion of the two pigments. The solu¬ 
bilities were determined in practically 
the same manner as were the solubili¬ 
ties of carotin ( 9 ). 
Table I shows the solubility of xan¬ 
thophyll in petroleum ether. The 
transmittancies given for all of the 
solvents are evaluated from graph 11, 
Figure 2 of a previous paper ( 8 ), for 
the quantitative determination of xan¬ 
thophyll in solution. The determi¬ 
nations when averaged show the solu¬ 
bility to be 9.51 mgm. per liter. 
Table I .—Solubility of xanthophyll in 
petroleum ether (B. P. 50 to 55° C .) 
at 25° C. 
Experi¬ 
ment 
No. 
Dilution 
Time in 
water 
bath 
Trans¬ 
mit- 
tancy 
XaE&o- 
phylrper 
liter 
Times 
Hours 
Mgm. 
1 
5 
22 
0.174 
9.10 
5 
70 
.140 
10.15 
2 
5 
42 
.174 
9.10 
5 
56 
.184 
8.80 
3 
5 
60 
.133 
10.40 
The results for absolute alcohol do 
not check as well as do those for the 
other solvents. It would seem that the 
later experiments reported in Table II 
were the best, for impurities in xantho¬ 
phyll tend to increase the amount of 
material held in solution. The average 
of the last two experiments has been 
taken as the solubility (201.5 mgm. per 
liter) of xanthophyll in absolute ethyl 
alcohol. 
The solubility determinations in ab¬ 
solute methyl alcohol are given in 
Table III. Only the data for experi¬ 
ments Nos. 2, 3, and 4 have been 
averaged for ascertaining the solubility 
in methyl alcohol, as there is some indi¬ 
cation that the first experiment gave 
too high a result. This average shows 
the solubility of xanthophyll in abso¬ 
lute methyl alcohol to be 134.9 mgm. 
per liter. 
