212 



Oxidation with Nitric Acid. — Several ccs. of the same 

 fraction were oxidised with dilute nitric acid (10 per cent.). 

 From the oxidised product two acids were separated ; 

 terephthalic acid, which was identified by its insolubility in 

 water, alcohol, ether, benzene, etc., and by its subliming on 

 heating ; and p-toluic acid, which was soluble in alcohol 

 and melted constantly at 179° C. The formation of these 

 acids indicated the probable presence of cymene. The middle 

 fraction of steam distillation A 5 was treated repeatedly with 

 a solution of resorcinol (50 per cent.). The oil unabsorbed 

 by resorcinol solution had a rotation of — 11*2, and was 

 shaken with a solution of sodium bisulphite (35 per cent.) to 

 remove any aldehydes which had not been polymerised by 

 the alkali treatment. The oil was separated and steam dis- 

 tilled. The specific gravity was 0"861 and the rotation 

 — 10*4°, showing that the bisulphite treatment had removed 

 some laevo-rotatory aldehyde. 



Schiff's reagent gave no immediate coloration, but a faint 

 violet developed on standing. 



The sample was distilled and collected in the following 

 fractions : — 



Temperature. 



Amount. 



Rota^ 

 tion. 



Specific 

 Gravity. 



Refract 

 Index. 



(a) 175°-178°C. 



(b) 178°-181°C. 



(c) 181°-186°C. 

 (d) Residue 



21 ccs. 

 16 ccs. 

 L3 ccs. 



- 9-38° 

 -10-14° 



- 9-2° 



- 1-7° 



0-8605 

 0-8619 



1-4820 

 1-4827 



On shaking the fraction marked (b) with a mixture of 

 four volumes of concentrated sulphuric acid and one volume 

 of water, allowing to stand for 24 hours separating, and 

 steam distilling, and repeating the whole process until no 

 further charring occurred, the residue so obtained had the 

 following constants: — Rotation, +0'16°; refractive index at 

 20° C, 1-4936; ' dispersion, 0-01374. These figures closely 

 approximate to those ascribed to cymene. 



Separation of Pure Cymene. — In order to separate pure 

 cymene, the oil unabsorbed by resorcinol solution from the 

 middle fraction of steam distillation A 5 was treated as 

 follows : — 



It was shaken with a solution of sodium hydroxide (15 

 per cent.), the oil separated and steam distilled in the presence 

 of caustic soda (digested with solid caustic soda) for several 

 hours, then heated for half a day with sodium metal and 

 again digested with solid caustic soda for one day. After 

 again steam distilling in the presence of caustic soda and 

 digesting with sodium metal and solid caustic soda several 

 times it was again distilled. The oil distilled between the 



