384 
Journal of Agricultural Research 
Vol. XXVI, No. 9 
From this review of the literature it is apparent that no accurate 
method for the estimation of carotin is readily available. Consequently, 
a rapid, accurate method for the determination of carotin by means of the 
spectrophotometer has been devised. 3 ' 4 
THE KONIG-MARTENS SPECTROPHOTOMETER 
definition of terms 
The manner of using the instrument (6) in color analysis is not new. 
A more recent discussion of the method and apparatus is to be found in 
a Bureau of Standards Scientific Paper (j), No. 440. In order that this 
paper may be better understood by those who are not yet familiar with 
the Konig-Martens Spectrophotometer, a brief explanation of the spectro- 
photometric terms used here will be given. 
When white light enters a column of colored solution the lights of 
different wave lengths are transmitted in unequal amounts. The blue 
to violet end of the spectrum is absorbed to a very great extent when 
light passes through a solution of carotin. In strong solutions all of the 
light is absorbed in this region (wave lengths of less than 500 millimicrons) 
and consequently none is transmitted. With a spectrophotometer it is 
possible to measure for any wave length the relative amount of light 
transmitted by a cell containing a solution, that is, the ratio 
light passing through last surface of ce ll 
light incident on first surface of cell. 
This ratio is called the transmission (T) for this wave length. 6 The 
Transmittance (T) of the column of colored solution is the ratio of the 
light arriving at the second colored-solution-glass surface to the light 
passing the first colored-solution-glass surface, i. e., this ratio refers to the 
liquid in the cell only. 
Further, the transmission of a given cell containing the solution is 
designated as (Sol T) while the transmission of the same or a duplicate 
cell containing pure solvent is designated as (Sov T ). Then, 
liol J T) = (Sov T^^Transmittancy, 
which is thus defined as the ratio of that fraction of the incident radiant 
energy which is transmitted by a cell containing the solution, to that 
fraction of incident radiant energy which is transmitted by the same or a 
duplicate cell containing the solvent. This transmittancy (T) is the 
quantity which is obtained from the measurements made on the Konig- 
Martens instrument. 
be_ 
The Specific Transmissivity = V T = t, where b = thickness (centi¬ 
meters) of the layer of solution and c= concentration (centigrams per 
liter) of the dissolved substance. 
The Specific Transmissive Index (others designate it as extinction 
coefficient or absorption index) =k=— log 10 2= — 1 log 10 T, i. e., bck= 
-log 10 T. ~l)c 
8 All spectrophotometric data given in this paper were obtained on the Konig-Martens spectrophotometer 
at the Bureau of Standards. 
* It is possible to use this method without making use of a spectrophotometer. A photometer, a mercury 
l am p and a filter to isolate line 435.8 are all that are necessary. See Bureau of Standards Tech, paper 
No. 119 ( 4 )• 
* The following symbols, terms and definitions are in accordance with those defined in the Preliminary 
Report of the Optical Society of America, Committee on Nomenclature and Standards of Colorimetry, 
Irwin G. Priest, Chairman. 1919. (Unpublished. A photostat copy may be consulted in the Bureau of 
Standards Library.) 
