— 118 — 



solutions up to a content of 5 mg. citral still showed distinct differences 

 in colour from milligram to milligram, whilst with a content of more 

 than 5 mg. citral the coloration became so intense that differences 

 could no longer be observed. Smaller differences than 1 mg. in the 

 content of the solutions could only be detected by us (by simple 

 comparison and without colorimeter), in the case of very weak solutions — 

 up to about 2 mg. citral- content. 



This, however, only applies to alcoholic solutions of citral, and 

 also to mixtures of citral and limonene, in which the citral-content 

 could be correctly determined by comparison with correspondingly 

 strong normal solutions, although it follows from what we have just 

 said, that we did not in every case arrive at such exact results as Chace. 



But with lemon oils, as Chace has already observed, the citral- 

 content cannot be determined with the same certainty; this is due 

 to the fact that, owing to the wax-like constituents contained in lemon 

 oil, the solution is here slightly turbid, which renders it impossible to 

 determine the tint of the red coloration with absolute precision. This, 

 however, may lead to considerable errors. If namely the proportionate 

 quantities indicated by Chace are taken as basis, the citral- quantity 

 found by the colour test must be multiplied with 1250 in order to 

 express the percentage of citral in the oil. Now, if there is any doubt 

 as to whether the tint indicates a citral-content of 3 mg. or one of 

 4 mg. (more exact distinctions it is, as a matter of fact, impossible to 

 make with lemon oil), it follows that the percentage of citral in the oil is 

 calculated either as 0,003 ' I2 5° = 3>75> or as o?oc>4 • 1250 = 5,0, 

 i. e., results which differ by 1,25 °/ . In view of the slight content 

 of citral in lemon oils, this margin is too large to recommend the 

 method (which is undoubtedly very useful for the citral-determination 

 in lemon extracts) also for lemon oils, — an opinion to which, for the 

 rest, Chace himself has given expression in his work. We have made 

 no tests to ascertain whether more exact results are obtained in lemon 

 oil by means of a colorimeter, but in view of the observations already 

 made, we must doubt this. 



Determination of phenols. Of the methods proposed for the 

 determination of phenols, the extraction with 5 per cent, soda liquor 

 indicated by Gildemeister 1 ) for thyme oil, has given the best results 

 in practice, as it is a method readily carried out and sufficiently exact 

 for practical purposes. Umney 2 ) subsequently extended the process 

 to clove oil, with the application of a 10 per cent, potash liquor. 

 But the results then obtained were too high by 10 to i2°/ , because 



*) Hager-Fischer-Hartwich, Kommentar zum Arzneibuch fur das Deutsche 

 Reich, 3rd Ed. 1892, Vol. II. p. 377. 



2 ) Pharmaceutical Journal 55 (1895), 951. 



