IGS On the Liquid Gum [Marcm^ 



IV. Alkalies, 



The pure alkalies render the liquid very dark coloured and 

 opake, so that it appears black, though in reality it is only of a 

 very deep brown. The compound does not precipitate with 

 glue, at least immediately. 



' The liquid sulphuret of potash occasions a copious yellow 

 coloured precipitate. 



When an acid is added to the alkaline solution^ the original 

 colour is gradually restored, and the liquid becomes again 

 transparent. 



V, Acids, 



The strong acids, namely, the sulphuric, nitric^ and muriaticj 

 Immediately precipitate a yellow or brown powder, and the liquid 

 retains its deep brown colour. 



Oxymuriatic acid immediately destroys the colour, renders the 

 solution transparent^ and throws down yellow flakes. The colour 

 is not again restoicd by adding an alkali. 



The tan was destroyed ; for the solution being evaporated^ 

 yielded only muriate of manganese, sulphate of lime, and a 

 little brown extractive insoluble in water. 



VI . Naiiire of the Solid Matter, 



The properties above detailed are sufficient to show us that the 

 substance which constitutes the essential part of our gum lies 

 intermediate between extractive and taoniu;, as they have been 

 described by chemists. 



it agrees with tao in being thrown down by glue, in convert- 

 ing skin into leather, and in precipitating most of the metallic 

 salts ; hot there are two species of tan, dilfering essentially from 

 each other in many respects. 



The first, for the sake of distinction, may be called the tannin 

 of nutgalls, or of oak bark. It is insoluble in alcohol, forms a 

 brown precipitate with glue, and a black with iron. Water is 

 its best solvent. In all these particulars our tannin differs 

 from it. 



The second species, which has been discovered by Hatchett, 

 STiay be called artificial tannin. It is soluble in alcohol, and 

 throws down iron and glue brown. Its taste is astringent and 

 bitter. Our tannin agrees more nearly with this species than the 

 preceding, though ihe differences are also considerable. Nitric 

 acid does not injure artificial tannin, but it converts the tannia 

 of liquid gjm to the bitter principle of W^elter. 



Extractive is distinguished by being soluble in water, and 

 "becoming insoluble by exposure to the air^ but continuing sqluble 



