12 1 



no crystalline precipitates are hereby formed, whilst this is often the 

 case with the bisulphite method, when it is impossible to read the 

 meniscus accurately. 



Burgess has made experiments with a whole series of aldehydes 

 and ketones, and has thereby found that the following compounds 

 give useful results: benzaldehyde, anisic aldehyde, cinnamic aldehyde, 

 citral, citronellal, cuminic aldehyde, nonylic aldehyde, decylic aldehyde, 

 carvone, and pulegone. In the case of citronellal, nonylic, decylic 

 and cuminic aldehydes, prolonged heating is necessary for a complete 

 conversion; with cuminic aldehyde and pulegone, it is convenient to 

 substitute litmus for phenol phthalein. 



With the help of the method under discussion, Burgess has also 

 ascertained the aldehyde- or ketone-content of various oils. We give 

 here the results: 



Cassia oil: 80 and 85°/ cinnamic aldehyde, 



Ceylon cinnamon oil: 68, 7 2 and 74°/ cinnamic aldehyde, 



Cumin oil: 2/\.°/ cuminic aldehyde, 



Dill oil: 5O°/ carvone, 



Spearmint oil: 62 °/ carvone, 



Caraway oil: 55 and 57% carvone, 



Oil of European pennyroyal: i6°/ pulegone. 



Whereas in most oils the determination of aldehyde or ketone 

 can be accomplished direct, Burgess recommends previous concen- 

 tration in the case of citron oil, lemon oil, limette oil, and oil of 

 sweet orange, owing to their low aldehyde-content. For this purpose 

 he takes 1 00 cc. oil, and at a pressure of at most 1 5 mm. distils off 

 90 cc. 1 ), when the residue is driven over with water vapour at ordinary 

 pressure. The quantity of the steam-distillate is accurately determined, 

 and from this in the above manner the aldehyde-content estimated. 

 By these means the citral - content ascertained was : in lemon oil 

 about 3°/o> in pressed limette oil about 8°/ , in citron oil about 4°/ , 

 in oil of sweet orange about 0,75 to i°/ . 



We have up to the present not yet made a sufficient number of 

 determinations by Burgess' method to form a conclusive opinion on 

 the process, but according to our present experience it appears to be 

 useful. Its principal value, as compared with the bisulphite method, 

 is in our opinion, that it is capable of more general application. But 

 we very much question the reliability of the method of citral- 

 determination (the " indirect " determination) recommended for lemon 

 oil etc., as the manner of concentration undoubtedly causes greater 



- 1 ) In order to test the oil at the same time for adulteration with turpentine 

 oil, the first I o cc. of the destillate are collected separately, and examined for their 

 optical behaviour. 



