3 6o 



HYDROBROMIC ACID METHOD. 



This method for the quantitative determination of cineol is a complicated 

 process, and not likely to become of general application ; besides it has no 

 advantage over more simple methods. Although the compound is formed in oils 

 somewhat poor in cineol, and is thus sometimes useful for qualitative work, 

 yet the process does not give a very stable product, and results are low. 



DISTILLATION METHOD. 



This method, which depends on the comparative ease with which cineol 

 crystallises at a low temperature, has also been suggested for the quantitative 

 determination of cineol (Helbing's Pharmacological Record, VIII, 1892.) It is 

 not possible, however, to remove all the cineol in this way, so that the process is 

 defective, and of little use for oils poor in cineol ; thus it is not of general 

 application. 



POTASSIUM PERMANGANATE METHOD. 



This method, proposed by F. D. Dodge (Journ. Industrial and Engineering 

 Chemistry, Vol. IV, August, 1912), is based on the fact that, in the cold, cineol is 

 practically .unacted upon by a dilute solution of potassium permanganate, while 

 many other constituents are oxidised into soluble compounds. The process has 

 not come into general use and the results are not always reliable. (See also 

 " Perfumery and Essential Oil Record," Nov., 1912, and Oct., 1913.) 



THE ARSENIC ACID METHOD. 



This method was proposed by J. L. Turner and R. C. Holmes in America 

 in 1914. It depends on the fact that arsenic acid of about 85 per cent, strength 

 combines with cineol to form a solid compound in the same way as does 

 phosphoric acid. The method is now official in the United States Pharmacopoeia, 

 where the process is fully described and directions given for carrying it out. 



It has been known for some time that cineol combines with arsenic acid 

 in this way, and a patent was taken out in Germany in 1901, Ger. Pat. No. 

 132,606 (1901), and also in the United States of America, U.S. Patent No. 705,545 

 (1902), covering the production of cineol from this compound. The method was 

 probably first applied for investigation purposes by Thorns and Molle for the 

 separation of cineol from the oil of Bay Laurel. (Arch, der Pharm. 242, 1904, 

 p. 172.) 



We do not think that arsenic acid can claim superiority over phosphoric 

 acid for the quantitative determination of cineol in Eucalyptus oils. We have 

 not been successful in obtaining concordant results with the same oil when using 

 the arsenic acid method quantitatively, and for that reason have ceased to use 

 the process. 



THE RESORCINOL METHOD. 



This method for the quantitative estimation of cineol in Eucalyptus oils 

 was first introduced by Schimmel and Co. in 1907 (semi-annual report for 

 October). The principle is based on the fact that cineol forms an addition 

 product with resorcinol, the compound being soluble in a 50 per cent, aqueous 

 solution of that substance. 



As first proposed the process, was faulty, as several other substances 

 which occur in the various Eucalyptus oils are absorbed at the same time as the 

 cineol. 



Later, Wiegand and Lehmann brought forward a modified process 

 (Chemiker Zeitung 32, 1908, 109), in which the oil was first fractionated, the 



