476 



Dr. A. W, Hofmann [April 11, 



ANALYSIS OF DIFFERENT COALS. 



:OAL 



A glance at this diagram shows you that the carbon in the several 

 specimens varies by more than 30 per cent., being 91*4 in Welsh anthra- 

 cite and 55*5 in Bohemian brown coal. Similar, though less marked, 

 discrepancies are perceptible in the other constituents. If you recollect, 

 in addition, that the nature of the compound atoms generated in the 

 distillation of coal must be influenced, moreover, by the temperature, 

 which again oscillates between limits widely apart, you cannot fail to 

 perceive that the destructive distillation of coal must be an almost 

 inexhaustible source of new compounds. 



The separation of the individual substances from the complex mix- 

 ture called coal-tar-oil appears, at the first glance, to present almost 

 insurmountable obstacles. But the principles made use of for this pur- 

 pose are very simple. The individual compounds contained in coal-tar- 

 oil may be separated in a great measure by distillation, their boiling 

 points varying, as may be seen by a glance at the diagram, to a con- 

 siderable extent. But additional means of purification offer themselves 

 in the different deportment which these substances exhibit under the 

 influence of chemical agents. I could not perhaps, in this respect, 

 bring under your notice a more instructive illustration than the 

 behaviour with acids and bases of the three coal-tar-oil-constituents, 

 repeatedly quoted. Benzol, phenol, and aniline may thus easily be 

 separated. To demonstrate this point experimentally, two glass 

 cylinders have been half-filled with benzol, two others with phenol, 

 and two further ones with aniline ; a solution of litmus having, 

 moreover, been added, each of the three substances is treated in one 

 cylinder with acid, in the other with alkali. In the case of benzol, 

 you observe, the indifferent hydrocarbon, insoluble both in acid and 

 alkali, floating colourless upon the coloured liquid ; phenol, being an 

 acid water-derivative, is not acted upon by the acid, but readily dis- 

 solves in the alkali ; aniline, lastly, being a well-defined ammonia- 



