ON VEGEtABtir MUCtLAGES* 3^ 



VAted from each other, yet I am inclined to believe, that this 

 is the case; and we may conjecture, with some degree of 

 plausibility, that thbse species are the most simple, that are 

 acted upon by the fewest reagents. In the first place 1 con- 

 sider gum arable ti:> be ft homogeneous substance ; and we h'^j^cge^ieous 

 may pro[.erly assign to it the specific name of gum, to which • nd gum by 

 it is entitled by long usage and general cons<^nt. Its preci- ^'^^ of emi- 

 pitation by silict»ted potash, and the orange coloured jelly 

 which it forms with the oxysulphate of iron, are sufficient to ^ aracters. 

 constitute its essential characters ; to which may be added 

 the milky precipitate which is formed by the addition of 

 alcohol to it, and the negative circumstance of its not being 

 affected by the nitro-muriate of tin. I am disposed to re- •> > 



erard as pure veffetabie mucus the substance procured from *r .1.1 



'-; "^ . o . ^ ^ V egetable mw 



hnseed. It is sufficiently characterized by the effect of the cus from Un- 

 superacetate of lead and the nitro-muriate of tin, and by ^^^^• 

 the manner in which it is precipitated by alcohol from its 

 aqueous solution ; these circumstances, as well as the nega- 

 tive operation of the oxysidphate of iron and the silicated 

 potash, serve to mark an obvious distinction between this 

 substance and gum. A third vegetable principle, which is 

 possessed of pecular physical properties, is starch. In its starch, 

 relations to the different chemical reagents it strongly re- 

 sembles mucus, although it differs from it in the manner in 

 which it is precipitated by alcohol. Gluten is a fourth sub- Gluten. 

 stance, in every respect essentially different from any which 

 we have hitherto examined. The most remarkable effect 

 produced upon it, by any of the chemical reagents, is the 

 change of colour induced by the nitrate of mercury, and the 

 copious precipitate by the addition of tan. 



In endeavouring to form an arrangement of vegetable 

 mucilages, and to assign definite characters for the primary ^x*^"^ °^ ^"^'' 

 substances, which enter into the composition, we must con- 

 sider to what degree of minuteness our subdivisions ought 

 to be extended. If, for instance, we meet with a body, 

 agreeing in every physical and chemical property witli gum 

 arable, except that it is not precipitated by silicated potash, 

 are we to regard this as a distinct vegetable principle, or sim- 

 ply as a variety of gum ? This latter opinion I should cer- 

 tainly be inclined to adopt ; for by indefinitely multiplyino- 



Qur 



