SECT. XV. RESINS. 433 



and when excited by friction their electricity is 

 negative. 



They are insoluble in water ; but most of them are 

 soluble in alcohol, and some of them in the fixed oils. 



When exposed to heat they inelt and afterwards 

 take fire, burning with a strong yellow flame, and 

 evolving a great deal of smoke. If subjected to 

 destructive distillation, the products are carburetted 

 hydrogene, and carbonic acid gas, a small portion of 

 acidulous water, and much empyreumatic oil. 



Resins are extremely numerous, like the oils from 

 which they are formed ; but the following are the 

 most distinguished : 



Rosin. From the different species of Pine 01 Species. 

 Fir-tree, there exudes a juice which concretes in 

 the form of tears. Its extrication is generally 

 aided by means of incisions, and it receives dif- 

 ferent appellations according to the species from 

 which it is obtained. If it is obtained from the 

 Pinus syhestriS) it is denominated common Tur- 

 pentine; from Pinus Larix, Venice Turpentine; 

 from Amyris Balsamea, Balsam of Canada. It 

 consists of two ingredients, oil of turpentine and 

 rosin. The oil is extricated by distillation, and the 

 rosin remains behind. If the distillation is con- 

 tinued to dryness, the residuum is common rosin or 

 colophonium ; but if water is mixed with it while yet 

 fluid, and incorporated by violent agitation, the resi- 

 duum is yellow rosin. The yellow rosin is the most 

 ductile, and the most generally used in the arts, 



VOL. j. 2 F 



