— ii7 — 



We consider the determination of such indices for judging the 

 value of essential oils, as less correct, and unnecessary, as a sufficient 

 number of unobjectionable constants is already taken into consideration 

 in the examination. The physical constants (specific gravity, rotatory 

 power, index of refraction, solubility) which can be easily and rapidly 

 determined, give in most cases sufficient information as to the quality 

 of the oils. If, in addition to this, serviceable methods of examination 

 are carried out for the purpose of quantitatively estimating individual 

 constituents or groups of compounds, such generalised methods as the 

 determination of the bromine number are superfluous, the more so as 

 the compounds which enter into reaction with the bromine are not 

 always known. It is desirable that the chemical methods of tests 

 are adapted to the peculiarity of the individual oil, and that the 

 investigators who occupy themselves with the working out of such 

 methods, concentrate their work upon discovering exact methods for 

 the direct determination of some important constituent of the oil, or 

 of the groups of bodies present in it, such as are, for example, at 

 our disposal in the saponification for the ester-determination, in the 

 acetylation for the estimation of the alcohols, in the bisulphite method 

 for the determination of aldehydes, and the like, some of which are 

 still open to improvement by suitable modifications. 



With regard to our own results with Mossler's method which 

 we have submitted to a test on eucalyptus oil, see under Eucalyptus 

 oil, p. 50. 



Hydroxyl determination. The behaviour of hydroxyl com- 

 pounds towards magnesium organic compounds has induced Tschugaeff x ) 

 to make use of magnesium-methyl iodide as a reagent on the hydroxyl- 

 group. As in this reaction one molecule methane is formed to every 

 hydroxylic hydrogen atom, Hibbert and Sudborough 2 ) endeavoured 

 to work out on this basis a quantitative method for the determination 

 of hydroxyl groups in organic compounds. By using amyl ether as 

 solvent for the magnesium organic compounds, and allowing the 

 reaction to be accomplished in a nitrogen atmosphere, they obtained 

 in a few cases satisfactory results, but in other cases the method 

 failed, probably owing to the insolubility of the substances in question 

 in the amyl ether. 



Th. Zerewitinoff 3 ) has now occupied himself in improving this 

 method, and he obtained good results by it, also when using amyl 

 ether as solvent for the substance to be examined. As a generally 

 appliable solvent he recommends pyridine, from which the water must 



>) Berl. Berichte 35 (1902), 3912; Report April 1903, 88. 



2 ) Proceed, chem. Soc. 19 (1903), 285. Chem. Zentralbl. 1904, I. 402. 



: ) Berl. Berichte 4-0 (1907), 2023. 



