FORMATION OF INDIGO-BLUE. 217 



quite lost the yellowish tinge which it showed at first and 

 until a portion of it on being mixed with acetate of lead and 

 ammonia gave a perfectly white precipitate. It was then 

 filtered again and evaporated either in the apparatus above 

 described by means of a current of air or over sulphuric acid. 

 The syrup left after evaporation was dissolved in alcohol and 

 the solution was mixed with twice its volume of ether, when 

 the indiglucine was precipitated as a pale yellow syrup, having 

 a sweetish taste. 



To the description formerly given of this substance I have 

 only a few particulars to add. Baryta water gives no pre- 

 cipitate in the watery solution, but on adding alcohol a slight 

 flocculent yellow precipitate is produced. The watery solu- 

 tion after being mixed with milk of lime and filtered is found 

 to have become strongly alkaline and on being boiled becomes 

 quite thick in consequence of the separation of a bulky yellow 

 mass of flocks, which on the liquid cooling is completely re- 

 dissolved forming a clear yellow solution as before, an experi- 

 ment which may be repeated any number of times. The 

 solution of the lime compound when mixed with an excess 

 of alcohol gives a bulky yellowish precipitate, after which the 

 liquid appears almost colourless. When treated with boiling 

 nitric acid indiglucine is decomposed and yields oxalic acid. 

 When a watery solution of indiglucine is mixed with yeast 

 and left to stand in a warm place no disengagement of gas 

 is observed nor is any sign of fermentation taking place 

 manifested. After some days however the solution begins 

 to acquire a strongly acid taste and reaction, showing that 

 it has entered into a state of acetous fermentation without 

 having passed through the intermediate stage of the alco- 

 holic fermentation. 



The new analyses which I have made of the lead compound 

 confirm the conclusion at which I arrived at an early period 

 of the investigation, viz. that when in combination with oxide 

 2 F 



