Dr. Schunck on the Formation of Indiffo-blue. 91 



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 compo- 

 sition : — 



683 100-00 10000 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 



C52H43NO'^6+13PbO. 



It appears, therefore, that the organic substances contained in 

 these lead compounds difi'er from one another merely by the ele- 

 ments of water ; and it may hence be inferred, with a great degree 

 of probability, that indican itself in a state of purity differs in com- 

 position from them merely by containing the elements of several 

 equivalents of water less. Assuming its composition to be repre- 

 sented by the formula C^^ H^ NO^^', it must be shown how this 

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

 be 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 de- 

 scribed, and dried in vacuo, was analysed with the following- 

 results : — 



I. 1-0580 grm., burnt with chromate of lead, gave 0-4550 

 grm. carbonic acid and 0-1670 water. 



0-7620 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 : — 

 H2 



