Easterfield and Bagley. — Chemistry of Colophony. 479 



(a.) Four hundred grams of colophony was distilled with a 

 rod and disc fractionation column at a pressure of 31 mm. 

 The portion distilling between 270-290 weighed 222 grms. 

 This was redistilled five times, at pressures varying from 

 27-35 mm. The second, fourth, fifth, and sixth distillates 

 were analysed, but the results only confirm the conclusion 

 arrived at in the preliminary experiment. The numbers ob- 

 tained were as follows : — 



Calcu- Calcu- Found 



lated for lated for 2nd 4th 



Isosylvic Anhyd. Abietic Acid. Distillate. Distillate. 



C = 81-9 C = 79-16 78-8 78-7 



H= 9-9 H= 9-72 9-6 9-5 



As the composition of the distillate had not changed during 

 six distillations, it was evidently useless to continue the 

 fractionation further. 



According to Bischoff and Nastvogel, the " anhydride " 

 dissolves in alkali, and when reprecipitated by dilute acetic 

 acid yields isosylvic acid melting at 61-63° C, and isomeric 

 with sylvic or abietic acid. The sixth distillate was accord- 

 ingly dissolved in potash, shaken out with ether to remove 

 any oily impurities, and reprecipitated according to Bischoff 's 

 and Nastvogel's directions. Two preparations melted respec- 

 tively at 65-73 and 67-80. The latter was recrystallized 

 from 80 per cent, alcohol, from which it separated in crystals, 

 having the characteristic crystalline form and melting-point 

 (160-165) of abietic acid. The evidence is thus complete for 

 the non-existence of isosylvic acid and its anhydride. 



The low melting-point of the precipitated acid as com- 

 pared with the crystalline acid is easily understood. The 

 precipitated acid is amorphous, and has no definite melting- 

 point. When once melted and kept a few degrees above its 

 melting-point it crystallizes. The crystals must then be 

 raised to a higher temperature before they melt. A number 

 of analogous cases might be quoted. 



Abietene. 



In the series of fractionations above described a small 

 quantity of low boiling-point material was invariably observed, 

 even in the last distillation. This indicated that even under 

 the most favourable circumstances a slow decomposition was 

 taking place, a conclusion that was supported by the fact that 

 even when the pressure was reduced to 11 mm. the liquid in 

 the distilling-flask did not bump. The most evident reaction 

 which might explain this phenomenon is that abietic acid is 

 losing carbon-dioxide and yielding the corresponding hydro- 

 carbon, the name of which should be "abietene," from 

 analogy in the case of benzoic acid and benzene. 



