4 BULLETIN 1036, U. S. DEPARTMENT OF AGRICULTURE. 
If the meaning of coal-tar creosote is to be imderstood, a definition 
of the mother liquors, or tars, from which the creosote is obtained is 
necessary. . 
Tar is denned as a nonaqueous, viscous liquid of very complex 
composition produced by the destructive distillation or partial com- 
bustion of organic matter or of minerals containing organic matter. 
Coal tar is the tarry liquid obtained by the destructive distillation 
or partial combustion of bituminous or semibituminous coals. 
EigJi-temperature tar is produced from bituminous or semibitumi- 
nous coal at temperatures so high that it contains principally aro- 
matic hydrocarbons, such as benzene, naphthalene, anthracene, and 
similar substances. It also contains well-defined amounts of pheno- 
loids and tar bases. The conditions for the manufacture of this high- 
temperature tar prevail in the usual gas-house retort and by-product 
coke oven. High-temperature tars are divided into two classes — 
retort tar and coke-oven tar. 
(1) Gas-house or retort tar is a high-temperature coal tar produced 
in a gas-house retort. Three types are recognized and derive their 
names from the type of retort in which the coal is coked . (a ) Hor izon tal- 
retort tar is a high-temperature coal tar produced in a horizontal gas- 
house retort; (b) inclined-retort tar is a high-temperature coal tar pro- 
duced in an inclined retort; (c) vertical-retort tar is a high-temperature 
coal tar produced in a vertical retort. 
(2) CoJce-oven or by-product tar is a high- temperature coal tar pro- 
duced in a coke oven from bituminous or semibituminous coal. At 
least three classes are made in this country and derive their names 
from the type of oven in which they are produced, (a) Otto tar is a 
high-temperature coal tar produced in the Otto, the United Otto, or 
the Otto-Hoffman coke oven; (b) Semet-Solvay tar is a high-temper- 
ture coal tar produced in a Semet-Solvay oven: (c) Koppers tar is a 
high-temperature coal tar produced in a Koppers coke oven. 
Low-temperature coal tar is produced from bituminous, semibitumi- 
nous, or cannel coal at such low temperatures that it contains hydro- 
carbons, principally of the paraffin or olefin series. It also usually 
contains large amounts of phenoloids and appreciable amounts of tar 
bases. Two general divisions are made — tars produced by destruc- 
tive distillation and producer gas tars. 
(1) Tars produced by destructive distillation include: (a) Cannel 
coal tars produced from cannel coal at relatively low temperatures. 
Cannel coal is in reality a highly bituminous shale, and if this tar is 
included under coal tars, then tars from other bituminous shales 
should also be included. Shale tar is produced from the bituminous 
shale found in southern Scotland, (b) Lignite tar is the tar produced 
by the distillation of lignite or brown coal. Lunge is the authority 
for the statement that this tar is produced in Europe for the manu- 
