— 12 1 — 



The standard of the phenyl hydrazin solution is determined as 

 follows: in a flask of one litre capacity are placed about 300 cc. 

 water and exactly 40 cc. decinormal iodine solution. Next, 10 cc. of the 

 phenyl hydrazin solution are allowed to flow from a burette in a small 

 flask containing about 50 cc. water, and the contents are gradually 

 added, while strongly shaken, to the litre flask. After about 1 minute, 

 it is titrated back with decinormal thiosulphate solution; 0,1 g. pure 

 phenyl hydrazin corresponds to 37 cc. decinormal iodine solution. 



Of the substances to be tested, 0,5 to 1,0 g. are weighed off in 

 a weighing glass, and in order to avoid oxidation a few cc. alcohol 

 are added immediately. The content of the weighing glass is then 

 washed with about 30 cc. alcohol in a quarter-litre flask, and so much 

 of the phenyl hydrazin solution is now allowed to flow in, that 1 mol. 

 phenyl hydrazin is present to every mol. of aldehyde (or ketone). The 

 mixture is then repeatedly strongly shaken, and left standing for 

 about 15 hours, protected from light, and with occasional shaking. It 

 is then diluted with water, and filtered through a folded filter (if the 

 liquid is not clear some plaster of Paris is added) into a litre flask 

 containing about 500 cc. water and 10 to 20 cc. decinormal iodine 

 solution, according to the quantity of phenyl hydrazin employed. 

 During the filtration it is necessary to agitate frequently. The filter 

 is well washed with water, and then the liquid, after adding some 

 starch solution, is titrated back with decinormal thiosulphate solution. 



The percentage x of aldehyde or ketone respectively is then 



d-M 



calculated according to the formula: x = , in which d re- 



100 • 4 - s 



presents the difference between the cc. decinormal iodine solution 



corresponding to the phenyl hydrazin used, and those used up during 



the test; M the molecular weight, s the quantity of the substance 



used in grams. 



Of oils with a very low content of aldehydes (lemon oil), about 

 log. are used for the analysis; after the reaction with phenyl hydrazin 

 they are separated in a separating funnel, and the titration only takes 

 place after repeated washing of the non-aldehydic portions. In such 

 case the samples analysed must be thoroughly shaken for a long time, 

 and left standing for about 20 hours. 



We were particularly interested in this Rother's process, as 

 the author also recommends it specially for the determination of 

 citral in lemon oil. For this reason we carried out check -tests, for 

 which we used mixtures of perfectly fresh pure citral with pinene and 

 limonene. It was then found that on the whole this method gives 

 reliable results, but that it has not, in respect of accuracy, any con- 

 siderable advantage over the volumetric bisulphite method and the 

 sulphite method; for practical use in technical work the new method 



