456 



RESINS 



So enormous is this industry in the United States that it is com- 

 puted that at least 800,000 acres of virgin forest are newly invaded 

 annually to supply the turpentine stills in operation. 



Description. The resin thus obtained should form pale amber- 

 coloured, transparent, glassy masses, very brittle and easily powdered. 

 It is rather heavier than water, the specific gravity varying from 1 -070 

 to 1-085 (Dieterich). It has a faint terebinthinate odour and taste. 

 At about 80 it softens, but it does not completely melt until the 

 temperature exceeds 100. It is soluble in alcohol, ether, and 

 chloroform, and leaves when incinerated but little ash. Freshly 



FIG. 240. Transverse section through the wood of Pinus maritima, 

 showing an oleo-resin duct, c. Magnified. (Tschirch.) 



powdered colophony is almost entirely soluble in petroleum spirit, 

 but becomes much less soluble by long keeping. A thin film of the resin 

 increases in weight by exposure to the air, a change probably due to 

 oxidation. 



Constituents. According to Tschirch and Studer (1903) American 

 colophony has the following approximate composition : 



a-Abietic acid . . . 30 per cent. 



/?-Abietic acid 22 



y-Abietie acid . . . 32 

 Resene ...... 5 



Volatile oil 0'5 



Bitter principle ..... trace 



The abietic acids are unstable crystalline isomeric acids to which 

 the formula C 20 H 28 O 2 is assigned. 



