24 
BULLETIX 1036, U. S. DEPARTMENT OE AGRICULTURE. 
tar from Youghiogheny and five from Westmoreland. In addition, 
three samples were taken from plants using Alabama coal and three 
from plants using mixed coal in the horizontal retorts. Certain 
earlier investigations at the Forest Products Laboratory had shown 
that the tar produced from at least one inclined-retort plant had 
certain peculiarities which at the time put it under the suspicion of 
having been contaminated with other tars. For this reason it 
seemed desirable to visit as many of these plants as could be con- 
veniently reached and determine whether these differences in proper- 
ties were peculiar to the one plant or whether they were character- 
istic of inclined-retort tar. Six samples of this tar were collected. 
At the time of the collection only two plants were using the vertical 
retort, and one of these was not in active operation. Therefore, only 
one sample of vertical-retort tar was taken. Approximately one- 
half of the by-product coke-oven plants then existing were visited. 
They included six Semet-Solvay, five Otto or Otto-Hoffman, and one 
Koppers oven plant. 
Table 8 shows the maximum temperature at which the coal was 
coked, and the specific gravity and free-carbon content of the tar 
produced by the different types of oven, as determined by the Office 
of Public Roads in 1912. 
Table 8. — Specific gravity and free-carbon content of various coJ:e-oven tars. 
Type of oven. 
Maximum. 
temperature 
of coal 
(°C). 
Specific 
gravity 
of tar at 
25° C 
Free- 
carbon 
con- 
tent. 
Type of oven. 
Maximum 
temperature 
of coal 
(°C). 
Specific 
gravity 
of tar at 
25° C. 
Free- 
carbon 
con- 
tent. 
1,388 
S>0 to 950 
950 to 1,150 
950 to 1. 150 
950 to 1, 150 
950 to 1, 150 
950 to 1.150 
950 to 1, 150 
950 to 1, 150 
950 to 1, 150 
950 to 1, 150 
950 to 1. 150 
950 to 1.150 
950 to 1,150 
1.171 
1.169 
1.195 
1.206 
1.176 
1.16S 
1.173 
1.191 
1.169 
1. 159 
1.181 
1.159 
1.141 
1.175 
3.>9 
2.73 
7.76 
8.77 
7.14 
6.10 
4.71 
7.49 
6.56 
6.07 
8.85 
5.05 
3.96 
6.90 
Otto-Hoffmann 
Do 
1,200 
1,000 
1.160 
1.214 
1.143 
1.160 
1.191 
1.179 
1.133 
1.176 
1.195 
1.182 
1.211 
1.210 
13.94 
Do 
14.05 
Do 
10.81 
Do 
Do 
1,111 
1,444 
1,222 
1.222 
1,222 
8.37 
Do 
Do 
United Otto 
Do 
7.89 
8.49 
Do 
Do 
5.21 
Do 
Do 
10.53 
Do. . 
Do 
12.18 
Do 
Do 
Do 
Do 
Do 
United Otto and 
Otto-Hoffmann. . 
Do 
United Otto and 
Rothberg 
833 to 1,055 
1,111 
1,000 
11.30 
12.40 
16. SO 
Attention is particularly directed to the low carbon content 
these tars. Of the 26 listed, only 8 have more than 10 per cent. 
A total of 36 specimens of coal tar reached the Forest Produ 
Laboratory in good condition. Three specimens were lost tlirou 
leakage in transit. Table 9 gives the type of retort or oven frc 
which the specimen tars were obtained, the kind of coal used, and « 
rough measure of the temperature used in coking. The tempera- 
tures shown for by-product tar were those given in Circular 97 of 
the Office of Public Roads for the same plants. For the most part 
