RESINS. 433 



The best labdanum is extremely rare ; this appears 

 under the form of dark-coloured masses, of the con- 

 sistence of soft plaster, becoming still softer on being- 

 handled. ' That which is collected on the leather 

 thongs is made up into long rolls, much harder than 

 the first, and not so dark. It is often greatly adulte- 

 rated by the admixture of black sand ; indeed both 

 kinds have of necessity a portion of fine sand in 

 combination, without which, independent of designed 

 abuses, they cannot be collected ; for the dust is blown 

 on the plant from the loose soil on which it grows, 

 and is unavoidably retained by the tenacious juice. 



Most of the resins above described are classed in 

 commerce among the gums, and have usually this 

 name affixed to them. They are, however, very im- 

 properly so termed, as it will be seen that resins and 

 gums have very distinct and opposite properties. 





