1813.] from Botany Bay, 167 



or nutgalls, by glue. Its colour is lighter, but it possesses all 

 the chemical characters of that precipitate. 



If a bit of fresh skin be steeped for some weeks in our aqueous 

 solution, it is converted into leather^ precisely as when steeped 

 in the infusion of oak bark. 



Hence it follows that the solid matter of our gum possesses 

 the essential character of tannin, 



II. Action of the Metalline Salts, 



All the metallic solutions which I tried occasioned precipitates 

 when dropped into the aqueous solution of the gum ; but none 

 of them rendered the solution colourless, except nitrate of 

 mercury. The following table exhibits the colour of the preci- 

 pitate, and of the supernatant liquid : — ^ 



Precipitate. Liquid. 



Nitrate of mercury Reddish brown . . . .Colourless. 



Corrosive sublimate O Muddy, and 



light coloured. 



Sulphate of copper Ochre yellow Brown. 



Sulphate of zinc Light brown ..... .Brown. 



Sulphate of iron ....... .Brown black Dark green. 



Nitrate of silver Dark grey Grey brown. 



Muriate of nickel Light yellow Light yellow. 



Muriate of arsenic Ditto Ditto. 



Muriate of manganese , » . .Grey brown Grey brown. 



Cuprate of ammonia Dark brown Dark brown. 



These precipitates, v/hen dried, assumed all of them a colour 

 more or less brown, none of which answered well as paints, at 

 least when used with water. The whole of the colouring matter 

 could not be thrown down by these salts. Hence it follows that 

 they form with it compounds to a certain degree soluble in water. 



III. Action of the Earths, 



The three soluble alkaline earths, barytes, strontian, and lime, 

 when dropped into the solution, throw down a beautiful dark 

 brown precipitate in flocks ; but the solution still continues 

 coloured, though an excess of the earthy waters be added. When 

 the precipitate is dried it retains its colour, is tasteless, but gives 

 a brown colour to water. 



Muriate of alumina likewise renders the solution brown and 

 opake, and a precipitate, falls after some hours, which does not 

 appear to be soluble in water. Neither muriate of magnesia, 

 nor muriate^ of barytes, occasions any change 5 neither is any 

 precipitate thrown down by silicated potash. 



