202 MR. E. SCHUNCK ON THE 



From these numbers I deduced the following composi- 

 tion : — 



Eqs. Calculated. II. III. 



Carbon 52 312 17.33 17.56 17.69 



Hydrogen 37 37 2.05 2.04 2.07 



Nitrogen 1 14 0.77 0.75 0.77 



Oxygen 40 320 17.80 17.69 18.01 



Oxide of Lead... 10 1117 62.05 61.96 61.46 



1800 100.00 100.00 100.00 



After deducting the oxide of lead, the amount of which is 

 unusually large for a compound of definite constitution, the 

 organic substance combined with it has the following com- 

 position : — 



Eqs. Calculated. II. III. 



Carbon 52 312 45.68 46.16 45.90 



Hydrogen 37 37 5.41 5.36 5.37 



Nitrogen 1 14 2.04 1.97 1.99 



Oxygen 40 320 46.87 46.51 46.74 



683 100.00 100.00 100.00 



An analysis which I made of a lead compound, prepared 

 directly from a watery extract of woad by precipitating with 

 acetate of lead, filtering and then adding ammonia to the 

 filtered liquid, gave a composition agreeing pretty well with 

 the formula C52 H43 NO46 + 13 PbO. 



It appears, therefore, that the organic substances con- 

 tained in these lead compounds differ from one another 

 merely by the elements of water; and it may hence be in- 

 ferred, with a great degree of probability, that indican itself 

 in a state of purity differs in composition from them merely 

 by containing the elements of several equivalents of water 

 less. Assuming its composition to be represented by the 

 formula 052 H33 NOgg, it must be shown how this formula 

 explains the formation of indigo-blue. Before this can be 



