314 PLANTS PRODUCING GUMS AND RESINS 



This is the broad classification, but there may be inter- 

 mediate stages in which the characters are not fixed. 



In contrast to gums, resins are substances partially or 

 totally soluble in alcohol, ether, chloroform, oil of turpentine, 

 petroleum, ether, &c. 



De Cordemoy gives the following definitions of various 

 resins : pure resins are solid bodies, most usually coloured, 

 amorphous or crystalline, which melt at a (usually) low 

 temperature. 



Natural resins are often mixtures of several resins, vary- 

 ing as regards their composition and properties, but which 

 may be isolated by the use of suitable solvents. 



Pure resins are less soluble than the above in a given 

 solvent. Natural resins are usually neutral, but some may 

 combine with alkalis to form resin soaps. 



The composition of resins is modified by heat. The 

 oxygen of the air has far-reaching effects on some, but on 

 others it has no action at all. 



The method of extracting resins varies according to the 

 plant, but the details are usually the same as for gums. 

 Resins exude naturally from trees, the flow being also 

 facilitated by incisions, or they are extracted from stems, &c., 

 by means of special solvents. 



GUM RESINS. 



Gum resins are substances with a density greater than 

 that of water and may be regarded as emulsions in water 

 of gums, resins, essential oils, tannin, and salts. 



Gum resins exude from plants in the liquid state, either 

 spontaneously or after incisions, and solidify after an ex- 

 posure to air of greater or less duration. 



We will retain our classification of Papilionace^, Cesal- 

 pine^e, and Mimose^e, and will give a list of the various 

 sorts of gums. 



