ANALYSIS, KEFINING, AND COMPOSITION. 17 



ferent constituents, and in this paper the three together will be desig- 

 nated as " pinene," unless for a special reason it is necessary to men- 

 tion the other constituents. 



DISTILLATION CURVES OF A WOOD TURPENTINE. 



The curves obtained by the distillation of a wood turpentine (fig. 

 54) show it to be so different in composition from the gum turpen- 

 tine just discussed that new points in the interpretation of the curves 

 are introduced. The first 70 to 75 per cent of the distillate could 

 well be, from the physical properties, a mixture of the same terpenes 

 which are the main constituents of the turpentine shown in figure 2, 

 the slightly lower physical properties being accounted for by smaller 

 proportions of either nopinene or camphene, or both. But between 

 the points where 70 and 95 per cent distill, the specific gravity of the 

 distillate decreases, while the boiling point and index of refraction 

 increase. This indicates the presence of some substance with higher 

 boiling point and higher index of refraction, but with lower gravity 

 than pinene. There is a terpene, dipentene, whose physical proper- 

 ties correspond well with those required by this substance; it has a 

 higher boiling point (175 C.), a lower specific gravity (0.849 at 

 15 C.), and higher index of refraction (1.471 at 15 C.) than 

 pinene ; it is known to be one of the products of the action of high 

 temperatures on pinene; 1 it has been identified as one of the con- 

 stituents of wood turpentines produced in Finland and Russia ; 2 

 and its presence in American " pine tar oil " has been indicated. 3 

 It is quite probable, therefore, that the substance whose presence is 

 indicated by the marked decrease in specific gravity of the frac- 

 tions as the boiling point approaches 175 C. is dipentene and that 

 it is formed from pinene by the high temperature employed in remov- 

 ing the turpentine from the wood. 



CHEMICAL IDENTIFICATION OF DIPENTENE. 



In order to make sure that dipentene was present in this turpen- 

 tine, however, an identification by chemical means was carried out. 

 By repeated fractional distillation and final distillation over sodium 

 a considerable quantity of material was obtained with boiling points 

 172 to 174.1 C., specific gravity 0.8527 at 15 C.,and index of refrac- 

 tion 1.4771 at 15 C. Part of this material was treated with bromine 

 in glacial acetic acid 4 and crystals were obtained which, after six 

 crystallizations from ethyl acetate, melted at 125 to 125.5 C. (di- 

 pentene tetrabromide 125 to 126 C.), thus substantiating the con- 



iWallach, Ann. Chem. 227, 282. 



2Aschan and Hjelt. Chem. Ztg. 18, 1566. 



3 Kremers, Pharm. Rev. 22, 150. 



4 Heusler-Pond, " Chemistry of the Terpenes," pp. 73 and 95. 



58637 Bull. 10513 3 



