Dec. 1,1923 Quantitative Determination of Carotin 397 
It was of great interest to know just what might be expected of such 
colorimeter readings, so checks on the method were attempted. In one 
case an unknown solution of carotin in ether was taken and readings 
made on the solution; this solution was then diluted to 50 per cent of its 
original strength, and again to 25 per cent; readings were then made on 
the three different concentrations of the carotin solutions. 
Table IX. —Lovibond slide readings obtained to determine the amount of carotin in 
the solution 
Concentration 
Lovibond slide reading. 
Respective carotin content as 
determined by each Lovi¬ 
bond slide. 
. 
Carotin content 
1 
per liter average. 
5 
10 
20 
s 
10 
20 
100. 
1.1 
1.6 
2.7 
i 
23-4 1 
24.8 
22 . O 
23.4x1 23.4 
50 . 
2.2 
3-5 
5.2 
IO.0 
10.4 
II .6 
IO. 7 X 2 21.4 
2 5 . 
3-8 
6.9 
”•5 
5-4 | 
I 
5 - 2 
5 *° 
5.5X4 22.0 
Perhaps a better way of securing the accuracy of the colorimeter 
readings would be to make direct comparisons with the spectrophotom¬ 
eter. In this way both of the methods could be checked. 
THE SPECTROPHOTOMETER AND THE COLORIMETER COMPARED AS 
TO ACCURACY IN DETERMINING THE CAROTIN CONTENT OF SOLU¬ 
TIONS 
In each of three flasks there was placed a small quantity of pure 
carotin; absolute alcohol was added to one flask, to another Squibb’s 
absolute ether (taken directly from the container) and to a third re¬ 
distilled petroleum ether (B. P. 30-50°). These flasks were stored in 
the ice box for 143 days, and from time to time their carotin content was 
determined both colorimetrically and spectrophotornetrically. 
Colorimetrically the carotin content was determined without dilution; 
but for the spectrophometer dilution was often found necessary because, 
in the case of carotin, the instrument is best adapted for use with solutions 
of low concentration. 
The results given in Table X show the variations in the readings 
obtained with the colorimeter and the spectrophotometer. 
Table X. —A comparison of results obtained on the same solution of carotin by means 
of the colorimeter and the spectrophotometer 
Age of solution in days. 
Absolute alcohol. 
S.o 
C. b 
O. 
Mgm 
3-6 4 
3-58 
3.68 
Mgm. 
24. 
3 ■ 9 
38. 
3.8 
50. 
0 * 1 
3-63 j 
7.60 1 
3 • 2 
71. 
3 • 3 
Ill. 
3-55 
3-54 | 
14 .-2. 
Absolute ether. 
Petroleum ether. 
S. 
C. 
s. C. 
Mgm. 
43 - 60 | 
10.12. 
6.32 ! 
3-24 I 
2.05 
1.16 
0.83 
Mgm. 
Mgm. Mgm. 
co.8o . 
s.? 
3-8 
. 45-0 
49.00 47.0 
49.00 41.0 
50.40 43.7 
CO.OO .. 
52.4O . 
° S=Sp ectrophotometric results. 
6 C*“ Colorimetric results. 
