BENZENE SERIES. AROMATIC COMPOUNDS. 367 



instance, not the tetra-methyl-benzene, but the para-methyl-propyl- 

 benzene, C 6 H 4 CH 3 .C 3 H 7 . This compound is of interest on account 

 of its close relation to the terpenes and camphors, which will be 

 spoken of later. 



Benzene, C 6 H 6 (Benzol). When coal-tar is distilled, products are 

 obtained which are either lighter or heavier than water, and by col- 

 lecting the distillate in water a separation into so called light oil 

 (floating on the water) and heavy oil (sinking beneath the water) is 

 accomplished. Benzene is found in the light oil and obtained from 

 it by distillation after phenol has been removed by treatment with 

 caustic soda and some basic substances by means of sulphuric acid. 

 Pure benzene may be obtained by heating benzoic acid with calcium 

 hydroxide : 



C 6 H 5 .CO 2 H + Ca(OH) 2 = = CaCO 3 + H 2 O + C 6 H 8 . 



Experiment 56. Mix 25 grammes of benzoic acid with 40 grammes of slaked 

 lime and distil from a dry flask, connected with a condenser. Add to the dis- 

 tilled fluid a little calcium chloride and redistil from a small flask. The 

 product obtained is pure benzene. Notice that it solidifies when placed in a 

 freezing mixture of ice and common salt. Observe the analogy between Ex- 

 periments 56 and 40. In one case a fatty acid is decomposed by an alkali with 

 liberation of methane, in the other an aromatic acid with liberation of benzene, 

 the carbonate of the decomposing hydroxide being formed in both cases. 



Pure benzene is a colorless, highly volatile liquid, having a peculiar, 

 aromatic odor and a specific gravity of 0.884; it boils at 80.5 C. 

 (177 F.) and solidifies at C. (32 F.) ; it is an excellent solvent 

 for fats, oils, resins, and many other organic substances. 



Nitro-benzene, C 6 H 5 .NO 2 . When benzene is treated with concen- 

 trated nitric acid, or with a mixture of nitric and sulphuric acids, 

 nitro-benzene is formed : 



C 6 H 6 + HN0 3 : : C 6 H 5 NO 2 + H 2 O. 



Experiment 57. Mix 50 c.c. of sulphuric acid with 25 c.c. nitric acid ; allow 

 to cool, place the vessel containing the mixture in water, and add gradually 5 

 c.c. of benzene, waiting after the addition of a few drops each time until the 

 reaction is over. Shake well until all benzene is dissolved and pour the liquid 

 into 300 c.c. of water. The yellow oil which sinks to the bottom is nitro- 

 benzene. It may be purified by washing with water and redistilling, after 

 removal of water and shaking with calcium chloride. 



Nitro-benzene is an almost colorless or yellowish oily liquid, which 

 is insoluble in water, has a specific gravity of 1.2, a boiling-point of 

 205 C. (401 F.), a sweetish taste, highly poisonous properties, even 



