92 Dr^ Schunck on the Formation of Indigo-blue. 



615-8 10000 10000 100-00 

 If the formula of the lead compound is C'^ H^ O'^ + 4PbO, it 

 is probable that the sugar in an uncombined state has the for- 

 mula C^^H^^O'^ It differs, therefore, from other kinds of 

 sugar by containing less hydrogen than is necessary to form 

 water with the oxygen. Its formula is, however, perfectly iu 

 accordance with the one which I have adopted for indican, viz. 

 Q52 JJ83 ]\TQ36_ jf ^g supposc the latter to take up two equiva- 

 lents of water, it will then simply split up into 1 equivalent of 

 indigo-blue and 3 equivalents of sugar, as will be seen by the 

 following equation : — 



1 eq. indican C^* U^ NO^^ _ fCi^ IP NO^ 1 eq. indigo-blue. 



2 eqs. water H^ 0^ / " XC^eH^o 0^^' 3 eqs. sugar. 



C52H35 N038 0^2^35^038 



I assume that the composition of the blue colouring matter 

 derived from indican is the same as that of indigo-blue, since an 

 examination of the properties of the former leaves little doubt 

 concerning their identity. I regret not having as yet been able 

 to ascertain by analysis whethei- this is the case or not, as I have 

 devoted the whole of the material at my disposal to an investi- 

 gation of the properties and composition of indican itself. 



I also assume that indican, in undergoing decomposition with 

 acids, splits up immediately into 1 equivalent of indigo-blue and 



3 equivalents of sugar. It is, however, possible that these three 

 equivalents of sugar may not be eliminated all at once ; and 

 from one analysis which I made, I should conclude that they 

 separated successively. Having extracted some dried woad leaves 

 with cold fether, I poured the setherial extract into a large bottle 

 and agitated it with about half its volume of cold water. The 

 tether was poured off, and the watery liquid was employed again 

 for agitation with several successive portions of a;therial extract 

 of woad. It acquired at last a dark yellow colour. The aether 

 contained in it was removed by spontaneous evaporation, and it 

 was then evaporated under a bell over sulphuric acid. At first 

 it yielded indigo-blue when boiled with sulphuric acid ; but the 

 evaporation having been conducted in too warm a place, the in- 

 dican contained in it became changed, and it ceased to give blue 

 flocks with acids. After the evaporation was completed there 

 was left a brown syrupy residue, which was redissolved in alcohol. 



