VoL XXVI, No. 9 
388 Journal of Agricultural Research 
limits of practicability, will give accurate values of transmittancy, which 
values may be readily used in quantitative work. However, the con¬ 
centration of this solution or thickness of the layer must be such as to 
bring the value of transmittancy within the range of the instrument for 
accurate measurement. 
The bright helium lines 447.2 and 501.6 and the bright mercury lines, 
yellow (576.9 + 579.1), green 546.1 and blue 435.8 were used in the pre¬ 
liminary work on carotin with the Konig-Martens instrument. Trans- 
mittancies were then determined for several dilutions of an ethereal 
carotin solution for each of these wave lengths of light. 9 
A scale of concentrations was chosen such that the values of — log 10 T 
obtained for these concentrations at a given thickness and wave length, 
will fall within the range of accurate measurement. If the concentra¬ 
tions are plotted on the X-axis and — log 10 T on the Y-axis, a line con¬ 
necting the points will extend diagonally across the chart. Then, from 
the measured transmittancy of an unkown solution, the concentration 
may be accurately determined from the graph. If the straight line 
runs almost parallel with the Y-axis then the range of the concentrations 
of the solutions relative to the range of the instrument would be too 
small, while if the line runs parallel with the X-axis then the difference 
in the transmittancy of the solutions would be too small for accurate 
work. The transmittancies of carotin solutions at wave lengths (576.9 + 
579.1), 546.1 and 435.8 for mercury vapor light are recorded in Table I. 
Table I. —Preliminary experiments on the transmittancy of solutions of carotin in 
U. S. P. ether® 
Wave length and light source. 
Transmit¬ 
tancy. 
Carotin per 
liter. 
Hg. ( 576 - 9 + 579 -i). 
O. 929 
% Mgm. 
42. OO 
0. 906 
37.80 
0. 910 
33 -60 
0. 969 
2 5 - 20 
0. 940 
l6. 80 
0. 990 
8. 40 
0. 999 
4. 20 
1. 000 
2. 10 
0. 996 
1.05 
Hg. (546.1). 
0. 801 
42. 00 
37.80 
0.843 
0.805 
33 -60 
0. 892 
25. 20 
0. 892 
l6. 80 
0. 948 
8. 40 
0.958 
4. 20 
1. 000 
2. 10 
0. 989 
1.05 
He:. (435.8). 
0. 032 
0. 172 
4. 20 
2. 10 
0 \ t rOD‘'-'/ . . 1 
0-365 
1.05 
° U. S. P. ether contains not less than 95.5 per cent nor more than 97.5 per cent of (CsKfchO, the remain¬ 
der consisting of alcohol containing a little water. 
& No attempt should be made to correlate data given in this table with data which follow, for they were 
used simply to ascertain which wave length would be most suitable for use. The carotin used here was 
not pure, nor was purity a requisite for the purpose for which the data were used. 
• The writer is greatly indebted to Irwin G. Priest, H. J. McNicholas and Dr. M. Katherine Frehafer 
of the Colorimetry Section of the Bureau of Standards for valuable assistance and many helpful sugges¬ 
tions regarding the work. 
