— 153 — 



Methods for the determination of citral in lemon oil are described 

 on p. 75. 



On the determination of the number of ethylene linkings in hydro- 

 aromatic bodies, see Chemical Notes, p. 165. 



Physical Notes. 



We have before us for comment several interesting papers by 

 A. Golodetz. 



1. "On new methods for the separation of mixtures with closely- 

 approximating boiling-points, and of mixtures which boil without decom- 

 position'' 1 ). For the purpose of separating mixtures of liquids the author 

 availed himself of the property of many mixtures of distilling at a tem- 

 perature, lower than the boiling-temperature of the pure components of 

 the mixture. To a binary solution distilled at minimum boiling-point, 

 which therefore cannot be completely separated by fractional distillation, 

 Golodetz adds a third body which also boils at minimum boiling-point 

 with one of the components of the mixture, and at a temperature which 

 must be lower than that of the binary mixture. 



Toluene, for example, boils at 110,4°, acetic acid at 118°. Now, if 

 a mixture in any proportion of these two liquids is distilled, there passes 

 over at 104° a distillate which is always composed of 31,9% by weight 

 of acetic acid and 68,1 % toluene, and upon increasing the distilling-tem- 

 perature there distils over the liquid which was present in excess of the 

 mixture-proportion mentioned above. Separation by fractional distillation 

 is therefore impossible by this method. It can be accomplished, never- 

 theless, when to the mixture a third body is added which distils over at 

 minimum boiling point with one of the two other components of the mix- 

 ture; that is to say, with the acetic acid if it is desired to keep back the 

 pure toluene in the evaporation, or with the toluene if it is desired to 

 keep back and gain the pure acetic acid. Such bodies are, in the first 

 place benzene, in the second, water. 



The author now made the following experiment: he mixed 68,1 g. 

 toluene with 31,9 g. acetic acid and, in order to be able to distil off the 

 acetic acid in the receiver, and to obtain the toluene in the pure form, 

 added a quantity of benzene corresponding to the composition of the 

 steam when benzene and acetic acid distil over together at minimum 

 foiling-point. In the present case this quantity was rather large (1800 g.), 

 for at minimum boiling point the mixture only contains 2% acetic acid 

 to 98% benzene. Golodetz distilled the entire mixture in a still with a 

 fractionating-head and obtained in the last fraction 46,1 g. pure toluene, 

 = 67,5% of the total quantity employed. 



2 ) Journ. russ. phys. chem. Ges. 43 (1911), 1041. Quoted from Chem. Zentralbl. 1912, I, 68. 



