possessing the Properties of Tannin. 59 



nitric acid, which readily formed it when applied to any sort 

 of coal • 



But I nevertheless suspected, ihatpossihly this substance, 

 or something similar to it, might be produced without abso- 

 lutely converting vegetable bodies into coal; for it seemed, as 

 I have observed in my former paper, that this only served 

 to separate the carbon in a great measure from the other 

 elementary principles (excepting oxygen) which v/ere com- 

 bined with it in the original substance, and thus to expose it 

 more completely to the effects of the nitric acid, as well as 

 to prevent the formation of the various acid products, which 

 are so constantly afforded by the organized substances when 

 thus treated. At first I had some thoughts of employing", 

 touchwood in this experiment : but not being able immedi- 

 ately to procure any, it occurred to me that indigo might 

 probably answer the purpose; for from some experiments 

 made by myself, as well as from those described by Berg- 

 man*, I well knew that the proportion of carbon in this 

 substance is very considerable. The following experiment 

 was therefore made : 



1 . On one hundred grains of fine indigo which had been 

 put into a long matrass, one ounce of nitric acid diluted with 

 iin equal quantity of water was poured ; and as the action of 

 the acid was almost immediate and extremely violent, an- 

 other ounce of water was added. When the effervescence 

 had nearly subsided, the vessel was placed in a sand-bath 

 during several days, until the whole of the liquid was 

 evaporated. 



On the residuum, which was of a deep orange colour, 

 three ounces of boiling distilled water were poured, by which 

 a considerable part was dissolved. 



The colour of the solution was a most beautiful deep yel- 

 low, and the bitter flavour of it surpassed in intensity that 

 of anv substance m my recollection ; it was examined by 

 the followmg reagents: 



Sulphate of iron produced a slight pale yellow precipitate. 



Mitrate of lime only rendered it a little turbid ; after which 



• Anahjtis Cfiermca Pigmcnti Indict. Opuscula Berg. torn. v. p. ZC. 



a small 



