SOME PHYSICAL AND CHEMICAL PROPERTIES OF 
CAROTIN AND THE PREPARATION OF THE PURE 
PIGMENT 1 
By F. M. Schertz 
Associate Biochemist in Soil Fertility Investigations , Bureau of Plant Industry , 
United States Department of Agriculture 
INTRODUCTION 
In a previous paper ( 6 ) 2 certain 
colorimetric and spectrophotometric 
data have been given for carotin. By 
using the graphs from these data the 
quantitative results presented herein 
have been obtained. The method of 
procedure for the preparation of the 
pure carotin used in obtaining the data 
for the graphs and the solubility deter¬ 
minations is given in detail in this 
paper. 
In connection with the solubility and 
with the quantitative determinations, 
it is essential to know what effect the 
solvent has upon the stability of the 
pigment in solution. Consequently, 
the keeping qualities of solutions of 
carotin have been studied. 
Some idea of the practical applica¬ 
tion of the data contained in this paper 
and in the previous one may be ob¬ 
tained by a brief examination of Palm¬ 
er’s book on “Carotinoids and Re¬ 
lated Pigments.” The data presented 
should be of especial value to those 
engaged in the manufacture and purifi¬ 
cation of vegetable oils, for the pig¬ 
ments present in the vegetable oils (§) 
are closely related in spectral transmis¬ 
sive properties to the carotinoids, and 
very likely they consist of carotin and 
xanthophyll. Parsons and Wilson (4) 
have shown in Plate 1, page 270, of 
their paper 3 the absorption curves for 
petroleum oils. These curves show 
very clearly that it is possible to grade 
the oils when the transmissivity of the 
oil in question is known. 
SOLUBILITY OF CAROTIN 
Absolute ether distilled over sodium, 
ethyl alcohol (99.7 to 100 per cent), and 
redistilled petroleum ether (benzin pe¬ 
troleum) which fractionates at 30° to 50° 
C., were the solvents used in the solu¬ 
bility tests. Impurities in the ether 
(1) affected the solubility of carotin so 
that it was necessary to allow the ether 
to stand over sodium for several days 
and then freshly distill just enough for 
use. 4 
All of the solubility tests reported 
were made in a constant-temperature 
water bath which was kept at 25° C. 
The time the solutions remained in the 
bath and the amount of stirring varied 
somewhat, but it is stated for each set 
of determinations. 
Either crystals of carotin freshly pre¬ 
pared, as will be described later in this 
paper, or those which had been kept in 
absolute alcohol in a sealed vial after 
filtering off and washing with low-boiling 
petroleum ether were used. They 
were dissolved in carbon disulphide or 
chloroform, and low-boiling petroleum 
ether was added to this solution. Crys¬ 
tals were obtained from this solution by 
evaporating the solvents under reduced 
pressure. The crystals were collected 
on a hardened filter in a small Buchner 
funnel and quickly washed two or three 
times with small portions of low-boiling 
petroleum ether, after which they were 
dried for 15 to 30 minutes in a well- 
evacuated desiccator. The melting 
point was quickly taken and if found 
satisfactory (174°) a small portion of 
the crystals was placed in each of two 
carefully cleaned bottles, which were 
partially filled with their respective 
solvents—alcohol or petroleum ether— 
and placed in the water bath for three 
hours, during which time the bottles 
were frequently shaken. 
In most cases 10 c. c. of the saturated 
solution were withdrawn from the 
bottle which had been kept in the water 
bath. By carefully tying a filter paper 
on the end of a pipette, 10 c. c. of the 
saturated solution of carotin could be 
1 Received for publication June 6, 1924; issued May, 1925. This paper is a report of an investigation 
on the four chloroplast pigments. 
2 Reference is made by number (italic) to “Literature cited,” p. 474. 
3 Spectrophotometric methods would undoubtedly be far more accurate than the method which they 
describe, and in addition would be simpler. The fact that all of the paraffin base oils (light and dark) have 
essentially the same light absorption curve makes the spectrophotometric methods even more useful in 
determining the grade of the oil. 
4 The impurities probably were peroxides, which may be removed by distilling the ether over sodium. 
Journal of Agricultural Research. 
Washington, D. C. 
( 469 ) 
Vol. XXX, No. 5 
Mar. 1, 1925 
Key No. G. 458 
