10 



BULLETIN 1036, TJ. S. DEPARTMENT OF AGRICULTURE. 



large number of different groups, of which those shown in the dia- 

 gram may be considered the simplest members of a few typical groups- 

 All of these compounds except naphthanthracene have been posi- 

 tively identified in coal tar, and very probably that one is present 

 also. Many more combinations and structures are, of course, possi- 

 ble, for which the reader is referred to Beilstein's Organische Chemie. 

 The general course of these reactions is probably somewhat as fol- 

 lows: Three acetylenes, CjHj, combine to form benzene, CgHg; 2 ben- 

 zenes unite to form diphenyl with the elimination of hydrogen; 1 

 benzene and 2 acetylenes combine to form naphthalene; 2 benzenes 

 and 1 acetylene combine to form phenanthrene or anthracene ; 1 ben- 

 zene, 1 naphthalene, and 1 acetylene combine to form either chrysene 

 or naphthanthracene. These reactions may take place in this manner 



GunjariQ 



H 

 /\ 



H C CM 



I I 



H C CM 



\/ 



c 



Nophrhotano 



C H 



lo <s 



He 



Anfhrocenv 



C H 



Id n 



/V C C CH 



\/ \/ 



c c 



H H 

 C 



\/ \ 



C CH 



H C C C C// 



c c c 



H H H„ 



H ' 



Diphanyl 



Z // 

 It m 



'f 



f— C CM 



c 



H H 

 C 



/ 



H C 

 Phan onrhrartQ \ 

 - .. .. C 



I* 'O \^ y'H 



>\ 



r. 



HC, C C vCA/ 



H 



HC 

 Chrysena \ 



/ 







\/\/" \/ 



*- ^ c c 



H C C C ^c Cff 



NQorhanrhrocana II 



C H /^ c ,C C C C// 



c c c c 



H ti H t1 



or through various intermediate stages. Part of these reactions, at 

 least, have been carried out on a laboratory scale; others have fol- 

 lowed the same general course, but have taken two or more stages 

 in which to accomplish the final result. 



From the above it is evident that, on the one hand, coal tars may 

 be obtained containing large amounts of paraffins if the secondary 

 and tertiary reactions are kept at a minimum; or, on the other hand, 

 tars containing a predominance of aromatic hydrocarbons if the sec- 

 ondary and tertiary reactions are complete or nearly so. All stages 

 of coal tars are known, from paraffin tars produced at low tempera- 

 tures to aromatic tars produced at high temperatures. The tars 

 generally used for the production of coal-tar creosote are those pro- 

 duced at high temperatures, but they may, under certain conditions, 

 contain low-temperature tars. These reactions are governed by the 



