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The compound substances found in vegetables 

 are, 1 gum, or mucilage, and its different modifica- 

 tions ; 2, starch ; 3, sugar ; 4, albumen ; 5, gluten ; 

 6, gum elastic ; 7, extract ; 8, tannin ; 9, indigo ; 

 10, narcotic principle ; 1 1, bitter principle ; 12, wax ; 

 13, resins ; 14, camphor ; 15, fixed oils ; 16, vola- 

 tile oils ; 17, woody fibre ; 18, acids ; 19, alkalies ; 

 earths, metallic oxides, and saline compounds. 



I shall describe generally the properties and 

 composition of these bodies, and the manner in which 

 they are procured. 



1. Gum is a substance which exudes from certain 

 trees ; it appears in the form of a thick fluid, but soon 

 hardens in the air, and becomes solid : when it is 

 white, or yellowish white, more or less transparent, 

 and somewhat brittle ; its specific gravity varies from 

 130O to 1490. 



There is a great variety of gums, but the best 

 know are gum arabic, gum Senegal, gum tragacanth, 

 and the gum of the plum or cherry tree. Gum is 

 soluble in v/ater, but not soluble in spirits of wine. If 

 a solution of gum be made in water, and spirits of 

 wine or alcohol be added to it, the gum separates in 

 the form of white flakes. Gum can be made to in- 

 flame only with difficulty ; much moisture is given off 

 in the process, which takes place with a dark smoke 

 and feeble blue flame, and a coal remains. 



The characteristic properties of gum are its easy 

 solubility in water, and its insolubility in alcohol. Dif- 

 ferent chemical substances have been proposed for 

 ascertaining the presence of gum, but there is reason 



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