128 Dr. Schunck on the Formation of Indigo-hlue. 



lead the composition of Indiglucine is expressed by the formula 

 C'^H^O", and that hence its formula, when in an uncombined 

 state, is probably C'^ H^o O'^. 



An analysis of the lead compound, prepared by adding acetate 

 of lead and ammonia to a watery solution of indiglucine, filtering, 

 washing and drying in vacuo, gave the following results : — 



OoGiO grra., burnt with chromate of lead, gave 0"24^30 grm. 

 carbonic acid and 0'0845 water. 



0-2495 grm. gave 0-2445 grm. sulphate of lead. 



These numbers lead, like those of the former analyses, to the 

 formula C^'^IPO^^ + 4PbO, as \\\\\ be seen by comparing the 

 numbers required by theory with those deduced from the ana- 

 lysis. 



There still remain some products of the action of acids on in- 

 dican to be treated of. These products are volatile. In order 

 to ascertain their nature, I took a solution of indican, mixed it 

 with sulphuric acid and boiled it in a retort, the tube of which 

 passed through a cork into a receiver from which a tube led into 

 a bottle with lime-water, the joinings being all air-tight. After 

 the liquid had entered into a state of ebullition and the air had 

 been expelled from the apparatus, bubbles of gas were seen now 

 and then to pass through the lime-water, which became milky 

 and deposited a quantity of carbonate of lime. After a great 

 part of the solution had been distilled, the receiver was removed, 

 and the liquid contained in it, which was yellowish and had an 

 acid reaction, was mixed with aii excess of carbonate of soda and 

 evaporated to dryness. The saline residue was mixed with an 

 excess of dilute sulphuric acid and the liquid was distilled. The 

 distillate was now colourless. It contained formic acid, for after 

 being neutralized and mixed with nitrate of silver, metallic silver 

 was soon deposited even in the cold. The whole of it was boiled 

 with carbonate of lead, and the filtered liquid was evaporated, 

 when it yielded some shining crystalline needles surrounded by 

 a thick syrup. By means of a little cold water, the sjTup was 

 removed, the needles being left undissolved. The latter had the 

 properties of formiate of lead. 



0-3450 grm. of these needles, dried at 100° C. and heated 

 with sulphuric acid, gave 0*3505 grm. sulphate of lead, equiva- 

 lent to 0-2579 oxide of lead or 74-75 per cent. In 100 parts of 



