19161 ISOPBENE FROM CoMMEECIAL TURPENTINES 155 



From the direct proof thus obtained it is evident that the 

 yield of isoprene from spirits of turpentine is due to pinene, 

 rather than to dipentene as claimed by Harries and Gottlob. 



THE VOLATILE OIL OF PINUS SEEOTINA 



This substance has been studied by Herty and Dickson ^ and 

 was found to be particularly rich in limonene. Since Harries 

 and Gottlob obtained 30 to 50 per cent of isoprene from com- 

 mercial limonene with the isoprene lamp, it seemed desirable to 

 study this volatile oil and compare its yield with that from 

 ordinary spirits of turpentine. 



In preparing the material from the oleoresin the difficulties 

 formerly met with in distillation by a current of superheated 

 steam were easily overcome by heating the oleoresin at a pressure 

 of one millimeter, the volatile oil readily passing off without any 

 tendency to froth in the flask and with largely decreased op- 

 portunity for polymerization during distillation. Table II 

 gives the results with the isoprene lamp. 



Table II 



ISTo further condensate could be obtained by continued 

 heating of the residue. As was to be expected the yield of 

 isoprene from this volatile oil, rich in limonene, shows a largely 

 increased yield, practically doubled, as compared with ordinary 

 spirits of turpentine. 



* J. Am. Ohem. Soc, 80, 872. 



