308 CHEMICAL DISCOVERY AND INVENTION 



quently with caustic soda which separates any carbolic acid 

 and the residual sulphuric acid. After washing with water the 

 hydrocarbons boiling between 80 and 150 C. are transferred 

 to the naphtha still. The accompanying photograph, Fig. 105, 

 taken in the works of Messrs. Major of Hull, represents one of 

 these stills with its rectifying column. The scaffolding shows that 

 the whole plant is about to be surrounded by a brick building. 



Fig. 106 shows the arrangement of the benzene rectifying 

 plant, of which a view is given in the preceding picture. 



The capacity of the boiler is about 5300 gallons, and it is 

 heated by steam. Its purpose is to separate from impure benzol 

 or naphtha the pure hydrocarbon benzene. In order to do this 

 it is necessary to provide for the condensation, from the vapour 

 which passes up the fractionating column, of those constituents 

 toluene (b.p. 110 C.), the xylenes (b.p. 137 to 142 C.), and 

 other hydrocarbons present in the crude benzol which boil at 

 temperatures above the boiling point of benzene (b.p. 80-5 C.). 

 With this object the column itself is divided by horizontal plates, 

 in each of which are placed a number of valves opening upwards, 

 and a tube open at top and bottom and projecting an inch or so 

 above the plate. The latter is thus kept covered with a layer of 

 liquid through which the vapour bubbles in its passage upward. 

 A further effect is produced by the tubes at the top of the column, 

 and the vapour which leaves it then passes into the cooling 

 arrangement furnished with thermometers by which the tem- 

 perature of the passing vapour is observed. From the cooler 

 any remaining vapour other than that of pure benzene is con- 

 densed and returned to the fractionating column by means of 

 the wr ought-iron pipes shown in the figure. The vapour of the 

 pure benzene then passes into the coil surrounded by cold water 

 and is thus delivered in the form of liquid into the receiver. 

 Benzene of any lower degree of purity can be obtained by simply 

 cutting off the connection between the cooler and the pipes 

 leading back to the column. 



With regard to the remaining fractions of the tar distillates 

 it will be sufficient to follow the course of three of them. 



Naphthalene is a white crystalline solid which melts at 79 C. 

 and boils at 218 C. It is contained in the light oils and in the 

 creosote oils. When the latter are stirred up with caustic soda 

 the carbolic and cresylic acids (phenol and cresol) present are 

 dissolved out and on standing the watery liquid separates from 



