— 59 - 



The last-named test is a much more sensitive one than the calcium 

 test. With a little practice it is even possible to estimate the quantity 

 of citric acid ester in the oil under examination by check-tests with oils 

 of known citric acid ester content. In the case of the two oils referred 

 to in this paragraph we thus ascertained the presence of about 2°/o tri- 

 ethyl citrate. The greatest care must however be taken when adding the 

 solution of permanganate of potassium, as otherwise peroxide of manganese 

 may easily be separated, which may lead to confusion with the precipitate 

 referred to above (mercury double-compound of the acetone dicarboxylic 

 acid). 



In the course of an examination of 6 guaranteed pure bergamot oils 

 by Deniges' method we were also able to detect traces of citric acid in 

 two of the samples. Here it is possible that the citric acid had been 

 carried into the oil from the pulp, which is rich in citric acid, during 

 pressing; in any case the proportions were too small to be of any prac- 

 tical importance. But if only l°/o triethyl citrate is added to such oils, 

 Deniges' test gives about ten times as heavy a precipitate. The residues 

 of evaporation of these authentic oils also gave lower saponifaction num- 

 bers; where this number exceeds 200 the oil is certainly suspect. 



The observations published above have appeared in similar form in 

 the Zeitschrift fur . angewandte Chemie of June last; vol. 23 (1910), p. 1018. 



Further attempts to apply! the method of examination described above 

 to the detection of other adulterations of bergamot oil and other essential 

 oils have remained without result. The reason is that, although all 

 the esters which have so far been observed as adulterants, viz. diethyl 

 succinate 1 ), glyceryl ester 2 ), diethyl oxalate 3 ), terpinyl acetate 4 ), and 

 tartaric acid esters 5 ), can partly only be evaporated with much difficulty 

 when heated on the water bath, they nevertheless volatilise entirely with 

 the oil-vapour when the evaporation-residue of bergamot oil is determined, 

 their behaviour in this respect being different from that of triethyl citrate. 

 Other experiments, however, led to the discovery of comparatively easy 

 and rapid tests by which adulteration with the above-mentioned esters could 

 be detected, and which might be sufficiently accurate for practical purposes. 

 We kept in mind as a necessary condition for the test, that often only 

 a small quantity of oil is available for examination, and that the method 

 of detecting any adulteration should, therefore, be one which can be carried 

 out with a minimum of material. 



The esters which come under consideration as adulterants may be 

 divided into two groups, viz.: 



x ) Report April 1897, 25; April 1905, 51. 

 2 ) Report April 1908, 64. 

 a ) Report April 1897, 25. 

 ') Report April 1910, 59. 

 5 ) Ibidem 90. 



