90 Dr. Schunck on the Formation of Indigo-blue. 



0"3790 grm. gave 0'3080 grin, sulphate of lead. 

 These numbers lead to the following composition : — 



Eqs. Calculated. Found. 



1670-3 100-00 100-00 



Notwithstanding the care, however, which I took in the pre- 

 pai-ation of tliis specimen, I found that it did not contain un- 

 changed indican, as a little of it when tested with sulphuric acid 

 gave no indigo-blue. It is, nevertheless, the purest specimen of 

 the lead compound which I have analysed ; that is to say, the 

 substance combined with the oxide of lead contained the least 

 amount of hydrogen and oxygen. 



The next analysis which I shall give, places in a striking light 

 the effect which alkalies exert on indican. I took some of the 

 same solution of indican which I had employed for the preceding 

 analysis, and which I found to give, when a little of it was boiled 

 with acid, very pure indigo-blue ; but. instead of evaporating it, 

 I added a large quantity of alcohol to it, and then precipitated 

 with acetate of lead and ammonia. The precipitate no longer 

 contained unchanged indican, and the substance combined with 

 the oxide of lead differed in composition from that of the pre- 

 ceding analysis by containing the elements of two equivalents 

 more of water. The third analysis was performed with a lead 

 compound made in the same way as that of the first analysis, 

 but from a specimen of indican prepared by the first method. 

 The composition I foimd to be exactly the same as that of the 

 compound of the second analysis. 



II. 1-0960 grm. dried in vacuo and burnt with oxide of copper 

 and chlorate of potash, gave 0-7060 grm. carbonic acid and 

 0-2020 water. 



1-5600 grm. gave 0-1880 grm. chloride of platinum and am- 

 monium. 



0-8930 grm. gave 0-7520 grm. sulphate of lead. 



III. 1-1000 grm. gave 0-7135 grm. carbonic acid and 0-2050 

 water. 



1-8350 grm. gave 0-2260 grm. chloride of platinum and 

 ammonium. 



0-5710 grm. gave 0-4770 grm. sulphate of lead. 



From these numbers I deduced the following composition : — 



