£12 EXPERIMENTS ON INDIGO. 



purple matter crystallized in small silky tufts at the summit 



of the retort : 6, a very bulky nitrogenous coal, yielding a 



prnssiate when calcined with potash: 7, some gasses, which 



I did not examine. 



Best mode of fhe purple matter being the principal object of mv re- 

 abfeihririg the , . ' ? , " , 



puruie E&aUer. search, it was necessary to have recourse to some other mode 



of obtaining it in a state of purity, for that I obtained by 

 distillation was contaminated with the oil, which arose with 

 it. The process that succeeded best with me was heating 

 in a platina or silver crucible, snrrounded by a charcoal fire, 

 5 dec. [7*7 grs] of indigo in fine powder; when the purple 

 matter crystallized in needles in the middle of the crucible. 

 It is necessary that the crucible be kept well closed during 

 the process, and also for some time after it is removed from 

 the furnace, otherwise the indigo would take fire. 



I shall describe below the properties of this sublimed mat- 

 ter, which had not wholly escaped the observation of Berg- 

 man ; merely observing here, that it is the indigo separated 

 from all those matters with which it is combined in what is 

 sold by this name. At present I shall proceed to examine 

 the nature of these substances, and the methods of separat- 

 ing them. 

 Analysis of in- Sect. II. Art. I. Indigo finely powdered was infused for 

 humid wav. twelv e hours in water heated to 90° or 100° F., in a closed 

 Action of wa- glass vessel. The decanted liquor retaining some indigo in 

 suspension, it wa? filtered ; and the indigo was exhausted 

 by repeated infusion and decoction. 

 Disox'genated a- These liquors being united and distilled yielded an 

 iaJigo. odoriferous water, a little ammoniacal ; and I suspect it 



contained also sulphur. Mean time a greenish powder was 

 precipitated from it, which assumed a blue colour from 

 contact with the air. This substance exhibited all the cha- 

 racters of indigo, whence I infer, that part of the indigo in 

 that of the shops is disoxigenated, and dissolves in water by 

 means of the ammonia. 

 Green matter. b. Long after the separation of the disoxigenated indigo, 

 a flocculent precipitate appeared of a peculiar substance, 

 which I shall call green matter ; and which had the follow- 

 ing properties, it is very littlg soluble in water, unless by 

 the intermedium of an alkali. It then assumes a reddish 



colour, 



