20G 



treated of are then described, of which we shall only mention one, 

 made to show the effects of heat upon it. 



Twenty grains of the substance, prepared by means of nitric acid 

 from pure vegetable charcoal, were subjected to a high degree of heat 

 in a glass retort. A small quantity of nitric acid, from which the 

 substance had not been entirely freed, first came over ; after this a 

 considerable quantity of ammonia was suddenly produced, which was 

 succeeded by carbonic acid and a small quantity of nitrogen gas. 

 A bulky coal, weighing 8^ grains, remained, which, by incineration, 

 yielded 1^ grain of brownish white ashes, consisting principally of 

 lime. 



Mr. Hatchett now relates an experiment made with indigo, by 

 which he ascertained, that a variety of the vegetable tanning sub- 

 stance might be formed without previously converting the vegetable 

 body into coal ; and he has, he says, since discovered, that although 

 indigo yields this substance more readily than most other vegetable 

 bodies, yet very few of those bodies are to be considered as excep- 

 tions. He had in his former paper stated, that in his experiments 

 upon common resin it was necessary to develope part of the carbon 

 in the state of coal by sulphuric acid, in order to produce the tanning 

 substance ; but he has since found, that when the abstraction of ni- 

 tric acid was several times repeated, that substance might be ob- 

 tained not only from common resin, but also from several other re- 

 sinous bodies. 



In the course of these experiments Mr. Hatchett found, that by 

 treating dragon's blood with nitric acid, a feather-like sublimate was 

 produced, which had the aspect, odour, and properties of benzoic 

 acid, although no vestige of this acid could be obtained by simply 

 exposing the dragon's blood to heat. Guaiacum, although similar in 

 its general character to resins, when treated as above, yielded only 

 slight vestiges of the tanning product, but, like the gums, afforded a 

 large quantity of oxalic acid. 



In the following section Mr. Hatchett observes, that the decoctions 

 of several roasted vegetable substances did not afford any precipitate 

 with a solution of isinglass ; even a decoction of coffee did not afford 

 a precipitate until several hours had elapsed ; but by adding a small 

 quantity of nitric acid to any of the above decoctions, the tanning 

 substance might be procured from them. 



Lastly, the author describes some experiments made by him in 

 order to procure the tanning substance from camphor. For this pur- 

 pose 100 grains of camphor were dissolved in sulphuric acid, and, 

 after four days, at which time the production of sulphureous acid gas 

 had nearly ceased, cold water was added, and the whole was sub- 

 jected to distillation ; by this, about 3 grains of an essential oil were 

 obtained ; and as by a second distillation with water no more essen- 

 tial oil came over, the residuum was treated with successive portions 

 of alcohol until that solvent ceased to act upon it. The residuum 

 had now the appearance of a compact coal, and after desiccation 

 weighed 53 grains. The solution formed by alcohol, upon being 



