Dec i, 1923 Quantitative Determination of Carotin 387 
It is readily observable that no interpolations are necessary other than 
a direct reading from the chart. 
Now, if we have transmittancy data for any given wave length and 
known concentration of a pure dye, to plot accurately a line, such as 
those above, then, by finding the transmittancy of any unknown concen¬ 
tration of the same dye, the amount of pigment present in the unknown 
concentration may be readily obtained from the graph. Hence, a rapid 
spectrophotometric method is obtained for the accurate determination 
of the concentration of any dye in solution which obeys Beer's law; the 
manner of using this method for the accurate determination of the amount 
of carotin in solution will be given in this paper. 
THE SPECTRAL TRANSMITTANCY OF CAROTIN, USING HELIUM AND 
MERCURY LIGHT; THE QUANTITATIVE DETERMINATION OF CAROTIN 
COMPARISON OF VALUES FOR THE DIFFERENT WAVE LENGTHS; SELECTION 
OF MOST SUITABLE WAVE LENGTH; SELECTION OF THE MOST SUITABLE 
CONCENTRATION OF CAROTIN 
Both white light and monochromatic light were available for use with 
the spectrophotometer. White light was obtained by reflecting the 
light of ten 600-watt gas-filled tungsten lamps from surfaces composed 
of magnesium oxide or carbonate (3). Helium or mercury lamps were 
the sources of the monochromatic light used. 
The strongest absorption of carotin is in the blue region of the spec¬ 
trum where the brightness of the white light is too low for accurate pho¬ 
tometric measurements. If the slit were widened to obtain sufficient 
field brightness, errors due to the wide slit and the continuous spectrum 
of the source of light would be introduced. 
In usin^the mercury and the helium lamps the scale of the instrument 
could be set on any one of the lines in their spectra, and the slit widened 
to increase the quantity of light admitted to the instrument, without 
introducing any error due to finite slit width. The brightness thus 
obtained was ample for precise photometric work at the following wave 
lengths: Hg*435.8: He447.2, He 501.6, Hg 546.1, Hg (576.9 + 579-0 and 
He 587.6. 
Transmittancy curves (3) obtained by the use of white light show the 
amount of transmittancy in the different regions of the spectrum and, 
consequently, by making a continuous curve of the absorption of any 
given solution, its concentration can be ascertained from curves drawn 
for known concentrations. This method for the determination of the 
carotin content is accurate but, as explained above, is quite tedious, for 
a great number of determinations would need to be made at different 
wave lengths. Now, in seeking a means by which only one determination 
on the spectrophotometer need be made so that the pigment content of 
any solution of carotin could be quickly and accurately determined, the 
complete transmittancy curve for one definite concentration must be 
known with a fair degree of accuracy. 8 
From wave length 500-720 the transmittancy of carotin is very high 
for all concentrations; the transmittancy curve for carotin shows bands 
below 500, that is, it is a region where the value of the transmittancy of 
carotin in solution changes rapidly, hence any line below 500, within the 
* The spectral transmission properties of carotin have been worked out by the Colorimetry Section of 
the Bureau of Standards and are to to be published soon. 
