M. du Bois-Reymond on the Eledricat Silure. 45 



These reactions seem to mc to prove the identity of this body 

 with the indirubine from indican, which, if it could be entirely 

 freed from all impurities, would no doubt exhibit the same pro- 

 perty of crystallizing and of volatilizing without residue*. 



The behaviour of indirubine towards concentrated sulphuric 

 acid and towards alkaline solutions of deoxidizing substances so 

 much resembles that of indigo-blue towards the same reagents, 

 as to lead one to expect a great similarity in the composition of 

 the two bodies, even if the" fact of their being formed fi'om the 

 same parent substance by the same process of decomposition were 

 unknown. The quantity of pure indirubine which I obtained 

 from the leaves of the ladigofera was only suflBcient for a general 

 examination of its properties, and for one analysis ; which showed, 

 however, if it be ])ermitted to draw a positive conclusion from 

 one determination, that it has exactly the same elementary com- 

 position as indigo-blue,— that the two substances are isomeric. 

 The following are the numbers yielded by the analysis : — 



0-3185 grm., dried at 100° C. and burnt with oxide of copper 

 and chlorate of potash, gave 0-8500 grm. carbonic acid and 

 0-1195 water. 



0-2021 grm. gave 49-3 cubic centims. of nitrogen at a tempe- 

 rature of 10°-5 C. and a pressure of 269-5 mdlims., equivalent 

 to 16-81 cubic, centims. at 0° C. and a pressure of 760 millims. 

 or 0-2122 grmt. 



In 100 parts it contained, therefore, — 



Carbon 72-78 



Hydrogen 4-16 



Nitrogen 10-50 



Oxygen 13-.56 



100-00 

 [To be continued.] 



VI. On the Electrical Silure. By M. du Bois-ReymondJ. 



AS long ago as the year 1855, spirit-specimens of the elec- 

 trical Silure were sent to Edinburgh amongst other remark- 

 able natural objects, by the Scotch missionaries from Creek Town 



* When dry woad-leaves are extracted with cold alcohol, the sides of 

 the L'liis^ vessel containing the extract generally become covered with 

 patches of suiull red crystals, which seem to consist of pure indnubiiie. 

 They arc insoluble in caustic alkalies, but soluble ni bodnig alcohol, tlie 

 solution depositing, on cooling, crystals exactly like those above described. 



t I owe this determination to Professor Fraiikland, who had the kind- 

 ness to perfonu it according to his own method of analysis. 



+ I'rom the BcTickt der Akad. du l\'isseiiscliaftai zu Berlin, August U, 

 1857, p. 424. 



