FORMATION OF INDIGO-BLUE. 203 



done, however, it is necessary to know the composition of 

 the sugar which is always formed simultaneously with the 

 indigo-blue. The lead compound of the sugar prepared as 

 above described, and dried in vacuo, was analyzed with the 

 following results : — 



I. 1.0580 grm. burnt with chromate of lead gave 0.4550 

 grm. carbonic acid and 0.1670 water. 



0.7G20 grm. gave 0.7490 grm. sulphate of lead. 



II. 1.0960 grm. after being dried in vacuo for some time 

 longer gave 0.4740 grm. carbonic acid and 0.1640 water. 



0.6420 grm. gave 0.6370 grm. sulphate of lead. 

 These numbers lead to the following composition : — 



Eqs. Calculated. I. II. 



Carbon 12 72 11.69 11.72 11.79 



Hydrogen 9 9 1.46 1.75 1.66 



Oxygen 11 88 14.30 14.21 13.55 



Oxide of Lead... 4 446.8 72.55 72.32 73.00 



615.8 100.00 100.00 100.00 



If the formula of the lead compound is C12 Hg On + 4 PbO, 

 it is probable that the sugar in an uncombined state has 

 the formula C12 Hjo O12. It diflfers, therefore, from other 

 kinds of sugar by containing less hydrogen than is necessary 

 to form water with the oxygen. Its formula is, however, 

 perfectly in accordance with the one which I have adopted 

 for indican, viz., C52 H33 NO^e. If we suppose the latter to 

 take up two equivalents of water, it will then simply split 

 up into I equivalent of indigo-blue and 3 equivalents of 

 sugar, as will be seen by the following equation: — 



1 eq. Indican C52 H33 N Oge) _JC,6 H5 N Oj 1 eq. Indigo-blue 



2 eqs. Water Ha O2 J (C38 Hgo O36 3 eqs. Sugar. 



CMH35NO38 C58H35NO38 



I assume that the composition of the blue colouring matter 

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



