248 
CHAS. E. SANDO 
curve of the pure endothine red is shown in figure 3, and, since the recovered 
pigment gave a similar curve, no doubt remains that the two compounds are 
identical. 1^ 
Practically none of the violet rays are transmitted ; in the blue and green 
SPECTRAL TRANSMISSION 
\US210) |D(5693) 
FBAUNHOFER LINES 
|C(6563) |B(607) la (716.5) 
360 400 420 440 46o 480 56o 520 540 560 SflO 600 620 640 660 660 700 
UiTKA-VioLET Violet Blue Green Yellow Orange Red 
720 740 760 
Wave length (meters k io-») 
Fig. 3. Curve of percentage of spectral transmission of encdothine red in alcoholic solution. 
Concentration, 0.00475 grams in i cc. 
portions of the spectrum there is slightly more transmission, while there 
is a gradually increasing transmission in the yellow, orange, and red portions. 
A combustion of the regenerated pigment furnished additional evidence 
of its identity with endothine red. 
.1662 gm. gave .3340 gm. CO2 and .0547 gm. H2O. 
Found C = 54.80, H = 3.68, O = 41.52. 
Required for C7H5O4 C = 54.88, H = 3.29, O = 40.83. 
Molecular weight determination. Endothine red itself could not be used 
for the determination of its molecular weight on account of its slight solu-' 
bility in solvents used for such determinations. It was found necessary, 
therefore, to use the diacetylendothine red for this purpose. The results 
with benzene as the solvent (K 2700) are reported in table 5. 
The writer is intJebted to Mr. I. C. Priest, of the Colorimeter Laboratory, Bureau 
of Standards, for this work. 
