ENDOTHIA PIGMENTS 249 
Table 5. Molecular Weight Determination of Diacetylendothine Red in Benzene 
hample 
Weight of 
Sample 
Weight of 
Solvent 
Elevation of the 
Boiling Point 
Molec. Wt, 
A 
.0741 
.0848 
.0881 
.2470 
15-0351 
.055° 
.085 
.065 
.205 
241.9 
1 79. 1 
2434 
216.3 
220.1 
237.07 
B 
C 
D 
Arithmetic mean of four determina- 
Required for 
C7H304(C2H30)2 
Disodium endothine red is formed on adding alcoholic sodium acetate to a 
boiling alcoholic solution of the coloring matter. It forms a "brownish 
olive" powder which is insoluble in alcohol, but readily soluble in water in 
which it gives a violet red solution. Apparently it undergoes no decom- 
position on boiling with water. The compound was dried at ioo° and 
analyzed by heating in a muffle furnace for 6 hours. 
.1600 gm. gave .0720 gm. Na2C03. Found Na = 19-55. 
.2106 gm. gave .0949 gm. Na2C03. Found Na = 19.57. 
C7H304Na2.2H20 requires Na = 19.77. 
The water of crystallization was not determined. At the time of deter- 
mination the possibility that the compound contained water of crystalliza- 
tion had not presented itself, and lack of material prevented further work 
on this point later. 
Monoharium endothine red, C7H304Ba.2H20, forms an olive-green felt- 
like mass when alcoholic barium acetate is added to a boiling alcoholic 
pigment solution. It is insoluble in cold water and in alcohol. 
.2714 gm. gave ,1638 gm. BaC03. Found Ba = 42.06. 
.2823 gm. gave .2011 gm. BaSOd. Found Ba = 4i.g2. 
C7H304Ba.2H20 requires Ba = 42.35. 
Theoretical Considerations 
In calculating the empirical formula for endothine red from the elemen- 
tary analysis, three formulas seemed to give figures which are in fairly close 
agreement with the experimental values. There seems to be no doubt that 
C^H^O^ represents the true formula of this 7tew coloring matter. Table 6 gives 
the data from which the selection of the assigned formula was made. 
The results of this investigation indicate that endothine red contains 
two hydroxyl groups and has acid properties which enable it to decompose 
alkali salts. Efforts to prepare an ester by prolonged digestion with alcohol 
and sulphuric acid in the usual manner failed. The acid properties can 
not, therefore, be ascribed to the presence of a carboxyl group. In this 
connection it is interesting to refer to the work of Perkin^^ which deals with 
^•^ Perkin, Arthur George. A reaction of some phenolic coloring matters. Journ. 
Chem. Soc. (London) Trans. 75: 433-454, 1899. 
