derived from Indigo-blue. 309 



indican by acids, and from which no indigo -blue can be ob- 

 tained, though they must be supposed to contain the elements 

 of that body and of various organic acids, such as formic, acetic 

 and propionic acids. Indeed the resemblance between the 

 two series of compounds extends also to their physical pro- 

 perties. For instance, the body A resembles indifulvine, 

 one of the products derived from indican, both being brownish - 

 yellow resins insoluble in alkalies. B is very similar to in- 

 diretine ; and D is so like indifuscine, that the two can hardly 

 be distinguished from one another. There may, in fact, be 

 some analogy in the composition of the two last-named 

 bodies. Indifuscine may, as I have shown on a former occa- 

 sion, be considered as a compound of indigo-blue and pro- 

 pionic acid minus water, as may be seen by the following 

 equation :- — 



Indifuscine. Indigo-blue. Propionic acid. 



C 4i H 20 N 2 O 10 + 2 HO=2(C 16 H 5 NO 2 ) + 2 (C 6 H 6 O 4 ). 

 In like manner D may be supposed to contain the same ele- 

 ments combined in a different proportion, since 



D. Indigo-blue. Propionic acid. 



C 56 H 24 N 2 O 10 +ioHO = 2 (C 16 H 5 NO 2 )+4(C 6 H 6 O 4 ). 



Analogies such as these, unsupported by experimental 

 proof, may be only fanciful. Nevertheless they may prove 

 of some use in facilitating the classification of facts. At all 

 events, the circumstance of indigo-blue yielding, by the com- 

 bined action of alcohol, acetic acid, and alkalies, bodies so 

 closely resembling the products obtained along with indigo- 

 blue in the decomposition of indican seems to afford a striking 

 confirmation of the view which I have taken regarding the 

 composition of these products. 



There is another point of view from which these bodies 

 may be considered. They may be represented as substitution 

 products of indigo-blue, one or more of the atoms of hydro- 

 gen in the latter being replaced by one or more organic radi- 

 cals. For instance, the body C may be looked upon as the 

 hydrate of a compound in which one atom of the hydrogen 

 of indigo-blue is replaced by phenyle (C 12 H 5 ), since 

 (^ 8 fl[ u ]SO 4 =,0 16 H 4 (C 12 H g )TO 2 +zHO. 



In order to obtain some confirmation for this hypothesis I 

 took some of the body D, of which 1 had a considerable quan- 

 tity, and which only differs from C by containing more water, 

 and subjected it to the action of hydriodic acid and phos- 

 phorus in a sealed tube. By the action of the nascent hydro- 

 gen I expected that indigo-blue might possibly be regene- 

 rated, but the experiment led only to a negative result ; for 

 though the tube was heated in the water-bath for several 



