Dec. i, 1923 
Quantitative Determination of Carotin 
395 
THE COLORIMETRIC METHOD OF DETERMINING CAROTIN 
Besides determining the amount of carotin in a solution spectrophoto- 
metrically it has been determined colorimetrically in the present work. 
Considerable work was done on the carotin content of many solutions, 
and it was for this purpose that the method which follows was devised. 
The method is based upon certain standard Lovibond slides, 5, 10, and 20 
yellow, used in connection with known solutions of carotin, which were 
matched in a Duboscq colorimeter. The Lovibond slide was placed 
on the left side on the stand which holds the cell (the cell remaining in 
position) and the solution of known concentration was placed in the 
cell on the right side. Care was taken that the right side gave exactly 
Fig. 5.—Lovibond slide readings plotted to show the results obtained from different concentrations 
of carotin in petroleum ether. 
a zero reading. The right cell was then adjusted so that the column of 
the liquid (carotin in petroleum ether, ether, or alcohol) matched the 
Lovibond slide. Curves were drawn from the readings obtained; the 
concentration in grams per liter is represented on the X-axis, while the 
depth in millimeters is plotted on the Y-axis. Each of the reported 
readings is an average of from 3-10 settings on the colorimeter. The 
results are averaged in the lower part of Tables VII and VIII, and from 
these the curves in Figures 4 and 5 are drawn. 
It was intended at first to use these curves for the accurate determin¬ 
ation of carotin in solutions, but the more accurate method with the 
spectrophotometer was later developed. The results of a reading on a 
solution of carotin in ether of unknown concentration by way of illus¬ 
tration will be cited here as an example. An average of 10 settings for 
each Lovibond slide gave 1.1 mm. for the 5 slide, 1.6 for the 10 slide and 
