FOKMATION OF INDIGO-BLUE. 189 



After (leduci >xide of lead the relative proportions of 



the other constituents are expressed by the following numbers: 



t. ii. m. iv. 



Carbon 50.15 48.36 47.80 



5.05 5.31 5.26 



Nitrogen 1 2.27 2.06 1.89 



Oxygen 12.87 05 



100 100.00 



These numbers conduct, as will be seen, to two different 

 formulae. The numbers of the first two determinations lead 

 to the formula C 52 H 31 N0 34 , those of the last two to the 

 formula C^ H33 N O x as a comparison of the numbers found 

 by experiment with those required by the respective formulae 

 will show : 



Eqs. Calculated. Eqs. Calculated. 



... 52 312 49.60 52 312 48.22 



Hydrogen. . 31 31 4.92 33 33 5.10 



Nitrogen . . 1 14 2.22 1 14 2.16 



Oxygen ... 34 272 43.26 36 288 44.52 



629 100.00 647 100.00 



The first analyses which I made of the lead compounds of 

 indican, and the results of which are recorded in the first part of 

 ; >aper, led to the formula? Cag H^ N O^ and C M H^ N O40, 

 but I stated at the same time that neither of these could be 

 considered as the true formula, since the compounds then 

 analysed seemed no longer to contain unchanged indican. 

 However the compounds, the analyses of which have just been 

 given, even after having. been completely dried, and decom- 

 posed with cold dilute sulphuric acid yielded solutions 

 which, after having been filtered from the sulphate of lead 

 and boiled, deposited flocks consisting almost entirely of 

 indigo-blue and indirubine, products indicating with cer- 

 ty the presence of unchanged indican. Since indican 

 exhibits a tendency, as I have before observed, to take up suc- 

 cessively a number of equivalents of water, it is probable that 



