— 47 — 



carry out the filtration in an absolutely dry atmosphere, there exists 

 here a further source of errors, and consequently neither the hydro- 

 bromic acid method can lay any claim to reliability. For this reason it 

 appears to us to say the least very risky, to make on the strength 

 of these methods definite statements with regard to the cineol- content 

 of eucalyptus oils. 



Cineol-determinations according to the hydrobromic 

 acid method, and the phosphoric acid method. 



Comf 



)Osition of the 

 per cent, by 



mixture 

 vol. 



in 



Results obtained 





Hydrobromic acid method 



Phosph 



oric acid method 



20°/o 



cineol, 



8o°/ 



turpentine oil 



20,1 °/ ; 19,5% 









40°/„ 



,, 



6o"/ 



,, 





39,8%; 32.4%; 23,6% 





— 



50% 



»5 



5o°/ 



,, 





45%; 41%; 28% 





42% 



60 7„ 



M 



40 "/ 



>> 





63°/ ; 54.8%; 45% 





53% 



70% 



5» 



30 °/o 



5» 











70% 



80% 



»5 



20 % 



J> 





77,9%: 73.8% 





— 



i°o°/o 



>» 



— 







93%; 92,7% 





— 



It is clear from the above table, and also from the one further 

 down, that most eucalyptus oils contain more cineol than is determined 

 by the hydrobromic acid or the phosphoric acid methods. 



The absence of a really reliable method of determination of cineol 

 has especially in recent times been felt more keenly, as nowadays in 

 the purchase of oils great value is often attached to certain guarantees 

 concerning their content of valuable constituents. 



We have now found that resorcinol is a suitable substance for the 

 quantitative separation of cineol from the oils. It is well known that 

 cineol also forms an addition-product with resorcinol 1 ). The compound 

 is already formed when cineol is shaken with an aqueous resorcinol 

 solution, and it represents in the crystallised state needle-shaped 

 crystals which melt at about 8o°. They dissolve readily in alcohol, 

 ether, and benzene, but with great difficulty in petroleum ether. 



This compound is distinctly more stable than the two addition- 

 products discussed above, but it also decomposes gradually on exposure 

 to the air — more rapidly in a vacuum — giving off eucalyptol, so 

 that finally only resorcinol is present. The same separation can also 

 be observed when the compound is heated with water or petrol- 

 eum ether. 



Attempts made to carry out the cineol - determination thus, that 

 the oil in question is shaken with resorcinol solution, the solid compound 

 separated off is removed from the oil and then decomposed in a 



a ) Berl. Berichte 35 (1902), 1209. 



