— 163 — 



Satie use xylene as a diluent, the same as was done by us in our tests, 

 and add five times the quantity by volume of this hydrocarbon to the oil 

 to be acetylated. In the case of Cayenne linaloe oil, which contains about 

 90% linalool, they determined by this method 70 to 91 °/o, while by acetyl- 

 ation of the undiluted oil only 45 to 52°/o alcohol could be obtained. 



In the experiments made by us at the time with pure linalool we 

 found that the quantitative acetylation of this alcohol leaves much to be 

 desired, even if it has been previously diluted with xylene. With one 

 hour's acetylation the results were quite unsatisfactory; the best values 

 were obtained when the time of acetylation was extended to about 

 7 hours, but even then they were almost always nearly 10°/o too low. 



For the determination of citral in extracts and oils of lemon, R. S. 

 Hiltner 1 ) recommends a colorimetric method which is based upon the fact 

 that a dilute alcoholic solution of m-phenylene-diamine hydrochloride at room- 

 temperature assumes a yellow colour upon the addition of citral, this colour 

 gaining in intensity as the proportion of citral is increased. The test is 

 applied with a l°/o solution of m-phenylene-diamine hydrochloride in 50°/o 

 alcohol. This solution, which preferably should be freshly prepared each 

 time, must be quite clear and colourless, and, if necessary, should be made 

 so by treating it with animal charcoal and filtering. The percentage of 

 citral in the extract or oil under examination is determined by comparative 

 tests with a solution of known citral-content (0,25 g. citral to 250 cc, 

 dissolved in 50°/o alcohol). 



The test is carried out as follows: — 1,5 to 2 g. lemon oil, or 25 g. 

 lemon-extract is diluted to 50 cc. with 90 to 95°/o alcohol; 2 cc. of this 

 solution is poured into the colorimeter-vessel, 10 cc. phenylenediamine 

 solution added, and the whole brought up to a fixed volume. Comparative 

 tests are made simultaneously in quite the same manner with the standard 

 solution referred to above, until the precise shade of colouring of the solution 

 under examination is reached. The citral-content of the oil or extract of 

 lemon can be calculated from the quantity of the standard solution taken 

 up in the test. If the citral-content is less than 0,1 °/o, it will be desirable 

 to use a little more of the solution under examination, in order to obtain 

 the intensity of colouring which is necessary to give exact results. 



It is said that the method answers satisfactorily. If, in accordance 

 with the instructions, the tests are conducted at room-temperature, the 

 reaction is neither affected by acetaldehyde which may be present in the 

 alcohol, nor by the other constituents of the oil of lemon. But where the 

 oil of lemon to be tested has undergone changes through oxidation, the 

 method cannot be used, because in such a case a yellowish-green to 

 greenish-blue colour (according to the degree of oxidation), is produced. 



*) Journ. of Ind. and Engin. Chem. 1 (1909), 798; quoted from Chem. Zentralbl. 1910, I. 1899. 



11* 



