60 Experimenis and Remarks on a Substance 



a sm.-ill portion of n-hiie powder subsided, which had the 

 characters o):' oxalate oF linic. 



Muriate ot" tin produced a copious white prccipitalCj which 

 afterwards chanocd to a yellowish-brown. 



Acetite of lead formed a very beautiful deep iomon-co- 

 loured precipitate^ which poiiibly niay prove useful as a 

 pigment. 



Ammonia rendered tlie colour much deeper; after which 

 the liquor became turbid, and a large quantity of fine yellow 

 spiculated crystals was deposited, which being dissolved m 

 water did not precipitate lime from its solutions. 



The flavour of these crystals was very bitter, and I suspect 

 them to be composed of ammonia combined with the bitter 

 principle first noticed by AVclther*. 



Lastly, when dissolved isinglass was added to the yellow 

 solution of indiifo, it inunediately became very turbid, and 

 a bright yellow substance was gradually deposited, and coated 

 the sides of the glass jar with a tough elastic film, which 

 was insoluble in boiling water, and possessed the characters 

 of gelatine combined with tanning matter. 



By this experiment I therefore ascertained, that a variety 

 of the artificial tanning substance could be formed without 

 previously converting the vegetable body into coal ; and I 

 have since discovered, that although indigo more readily 

 yields this substance than most of the other vegetable bodies, 

 vet in fact, verv few of these can be regarded as exceptions, 

 when subjected to repeated digestion and distillation with 

 nitric acid. 



2. — A. In my former paper I hzve stated, that commoa 

 resin, when treated with nitric acid, yielded a pale yellow 

 solution with water, which did not precipitate gelatine, and 

 that it was requisite to develop part of the carbon in the 

 state of coal by sulphuric acid, before any of the tanning 

 substance could be produced ; but having again made some 

 of these experiments, I repeated the abstraction of nitric acid 

 several times, and then observed, that the solution of rcsii^ 

 liti water acted upon gelatine similar to the solution of indigo 



• Thotr.^cii's Sy^ten! of Chemistry, 2tl edit. vc!. iv. p. £16'. 



which 



