C 68 ] 



to believe that few of them afford accurate results ; and 

 most of them (particularly the metallic salts,) which 

 produce changes in solutions of gum, may be conceiv- 

 ed to act rather upon some saline compounds existing 

 in the gum, than upon the pure vegetable principle. 

 Dr. Thomson has proposed an aqueous solution of 

 silica in potassa as a test of the presence of gum in 

 solutions he states that the gum and silica are pre- 

 cipitated together this test, however, cannot be ap- 

 plied with correct results in cases when acids are 

 present. 



Mucilage must be considered as a variety of gum; 

 it agrees with it in its most important properties, but 

 seems to have less attraction for water. According 

 to Hermbstadt, when gum and mucilage are dissolved 

 together in water, the mucilage may be separated by 

 means of sulphuric acid mucilage may be procured 

 from linseed, from the bulbs of the hyacinth, from 

 the leaves of the marsh-mallows ; from several of the 

 lichens, and from many other vegetable substances. 



From the analysis of M. M. Gay Lussac and 

 Thenard, it appears that gum arabic contains in 100 

 parts : 



of carbon 42,23 



oxygene - 50,84 



hydrogene . . . 6,93 

 with a small quantity of saline and earthy matter. 



or of carbon . - . 42,23 



oxygene and hydrogene in the pro- 1 

 portions necessary to form water J 





