Pr. Schunek on the Formation of Indigo-blue. 187 



no longer gives any indigo-blue when a portion of it is boiled 

 with sulphuric acid. If it be now evaporated in the same appa- 

 ratus as that used for evaporation of solutions of indican, it 

 leaves a brown syrup, a great part of which dissolves in alcohol. 

 On adding aether to the alcoholic solution, a syrupy deposit of 

 indiglucine is produced, followed by the separation of crystals of 

 leucine. If the liquid be filtered and evaporated, it leaves a 

 brown glutinous residue, having the properties of indicanine. 

 The lead compound, which was obtained in the form of a sulphur- 

 yellow precipitate by adding acetate of lead to the alcoholic solu- 

 tion, was, after being filtered off and washed with alcohol, sub- 

 mitted to analysis, when it gave the following results : — 



1'2580 grm., dried first in vacuo and then in the water-bath, 

 gave 0"8320 grm. carbonic acid and 0"2040 water. 



1*5655 grm. gave 0*2740 grm. chloride of platinum and am- 

 monium. 



0*7620 grm. gave 0*6610 grm. sulphate of lead. 



These numbers correspond in 100 parts to — 



Carbon 18*03 



Hydrogen 1*80 



Nitrogen 1*09 



Oxygen . • 15*26 



Oxide of lead 63*82 



100*00 



The oxide of lead being deducted, the substance combined 

 with it was found to have a composition agreeing with the for- 

 mula C^° H^'* NO^^, as will be seen by a comparison of the cal- 

 culated composition with that found by experiment : — 



Eqs. Calculated. Found. 



Carbon ... 40 240 50*20 49*85 



Hydro-en . . 24 24 5*02 4*98 



Nitrogen . . 1 14 2*92 3*01 



Oxygen ... 25 200 41*86 42*16 



478 100*00 100*00 



When a watery solution of indican or indicanine is evaporated 

 in contact with the air, cither spontaneously or with the assist- 

 ance of heat, a portion of it is always converted into a substance 

 which is insoluble not only in ajther but also in alcohol. That 

 the formation of this substance is due to the action of oxygen 

 on indicanine is proved by analysis. Its formation, moreover, 

 is promoted by heating the solution of indicanine with peroxide 

 of lead, the filtered liquid, after the dissolved lead has been 



