EMPYREUMATIC OILS, ETC. 393 



are distilled with 1 volume strong sulphuric acid, carefully 

 regulating the heat. Two layers of liquid then collect in the 

 receiver; the upper consists of very impure mesitylene and the 

 lower contains sulpliurous and acetic acids, resulting from a 

 secondary decomposition. The upper layer is drawn oft' and 

 rectified, first over the water-bath to separate undecomposed 

 acetone, and then over the naked fire ; but the product thus 

 obtained does not exhibit a constant boiling point, and requires to 

 be purified by numerous rectifications, and according to Cahours,* 

 final distillation over phosphoric acid. It is a very light, 

 colourless, strongly refractive liquid, having a slight, somewhat 

 alliaceous, but not unpleasant odour. It boils between 155*^ and 

 160° C. according to Hoffmann's observation, but Cahours 

 determined it between 162° and 164° C. 



Mesityhnic acid, CgH-^oO., or as now formulated, Cg Hg 

 (CHy)^ COo H. An acid isomeric with Xylic acid, and related 

 to mesitylene in the same manner as benzoic acid to Toluene. It 

 is prepared by boiling mesitylene for 16 to 20 hours with nitric 

 acid of sp. gr. 1*4, to which two volumes of water have been added. 

 The product is then, after complete oxidation, gently diluted with 

 a large quantity of water and submitted to distillation. 

 Nitromesitylene passes over first and then the acid, the distillation 

 being continued until crystals of this are no longer deposited in 

 the condensing: tube, water beins; added to the residue in the 

 retort as often as necessary. The acid suspended in the distillate 

 is collected on a filter. The portion which still remains dissolved 

 is obtained by neutralising the filtrate with sodium carbonate, 

 evaporating to a small bulk and decomposing with hydrochloric 

 acid. The acid thus obtained is added to that deposited on the 

 sides of the condensing tube and to that remaining on the filter, 

 which forms the larger portion. For complete purification the 

 whole is boiled for some time with a small quantity of tin and 

 concentrated hydrochloric acid, in order to remove any nitro- 

 compounds, and ^the portion which remains undissolved, on cooling, 

 is washed with water, dissolved in sodium carbonate and liberated 

 by the addition of hydrochloric acid to the solution at the boiling 

 point. The pure mesitylenic acid separates out on cooling, in 

 dazzling white crystals. 



* Comptes Rendus, xxiv., p. 255. 



