ANALYSIS OF THE YELLOW GUM. 2\5 



derable evolution of nitrous gas was produced, and the re- ^'f^^ited -with 

 sin was completely dissolved. The liquor remaining in the "^ "^^" * 

 retort deposited by cooling a crystalline substance; and 

 both the mother-water and the crystals were of a deep yel- 

 low colour, a very bitter taste, and a smell of bitter almonds. 

 A portion of the mother-water being saturated with potash, 

 it did not emit any sensible ammoniacal smell; but being 

 mixed with a solution of sulphate of iron, and supersaturated 

 with concentrated sulphuric acid, it let fall in the course of 

 the night a considerable quantity of Prussian blue. Ano- 

 ther portion of the same mother-water yielded on evapora- 

 tion thin crystals several lines square, which might be known 

 for oxalic acid. Their solution precipitated lime-waler, and 

 the calcareous salts. 



From the experiments I have related it appears, that the Conclusioab, 

 yellow substance, which flows from the xanthorrhoea, is com- 

 posed of a large portion of resin, combined with a few hun- 

 dredths of a kind of spongy gum, insoluble iu water, of ben- 

 zoic acid, and of a very acrid, yellowish volatile oil, very 

 pleasant to the smell. 



The yellowish substance of the xanthorrhcEa then cannot It is properlja 

 be considered as a resin, properly so called ; since it differs ^•'^'^' 

 from resins in containing benzoic acid, to which it is in- 

 debted at least in some measure for its pleasant smell ; and 

 on this account it seems to belong rather to the balsams, 

 than to the resins. 



What struck me most in the examination of this ydlow Resembles 

 substance is its resemblance to that matter, which the bees P''*^P*^''^' 

 employ for stopping cracks in their hives, and to which the 

 name of propolis has been given. 



This resinous, odoriferous matter, when separated from 

 the wax, by which its properties are concealed, exhibits the 

 characters of the yellow substance ; and, if subjected to the 

 same processes, comports itself in the same manner. 



It is considered by naturalists as ascertained almost to a The resin on 

 demonstration, that the resinous matter, which covers the ^"^^Yr. " ^ 

 buds of poplar trees, and preserves them from moisture, is 

 that which the bees so carefully collect, to form tlieir propo- 

 lis. The smell of this matter, which is precisely tlie same 

 with that of the propolis, strongly supports this opinion. 



The 



