26 
BULLETIN" 1036, U. S. DEPARTMENT OF AGRICULTURE. 
Table 10. — Water-gas tars used in experimental work. 
Tar 
num- 
ber. 
Kind of oil 
used. 
Temperature regulation. 
Plant man- 
ufactures 
coal gas 
also. 
37 
38 
39 
40 
41 
42 
43 
44 
45 
46 
47 
48 
49 
50 
51 
52 
53 
54 
Gas 
do 
do 
do 
do 
do 
do 
do 
do 
do 
do 
do 
do 
do 
do 
do 
do 
do 
None 
No. 
No. 
Yes. 
Yes. 
Yes. 
Yes. 
Yes. 
Yes. 
Yes. 
Yes. 
No. 
No. 
No. 
No. 
Yes. 
No. 
Yes. 
Yes. 
do 
do 
do 
do 
do 
do 
Yes (1,360° to 1,400° F.)... 
No 
Yes (1,350° to 1,400° F.)-.. 
No 
do 
Yes (1,300° to 1,400° F.)... 
do 
do 
No 
Yes (1,300° to 1,400° F.) . . . 
No 
The apparatus used for distilling the tars is shown in figure 11. 
The still proper, A, consists of an ordinary 2-gallon cast-iron pot 
still with a wide top clamped gas-tight. This still was mounted in 
an iron framework and suitably shielded with asbestos boards. It 
was tapped at the bottom, and a connection made with J-inch gas 
pipes, B, to permit the entrance of more tar and to serve as an inlet 
for air. This pipe was also provided with a union, so that after 
distillation the upright part could be turned down and serve as an 
exit for the molten pitch. The gooseneck on the still was changed 
somewhat, in order to admit of the use of a thermometer T, and also 
to provide for a peep sight P, at the top of the still. In making the 
peep sight, two pieces of brass tubing were threaded to fit a f-inch 
cross. In the threaded ends of these tubes were cemented two pieces 
of glass tubing containing a flattened bulb at the end. When the 
brass tubes were inserted in their proper places, the two glass surfaces 
were from one-fourth to one-half inch apart. This peep sight pro- 
vided an indication as to the working of the still. One of the greatest 
difficulties encountered in the distillation of the tar was the frothing 
over of the still caused by the presence of moisture. When this 
occurred, the peep sight was blackened, and the operator had a 
fraction of a second in which to turn off the gas and air and adjust 
the three-way cock E, to catch the undistilled tar in a separate 
container, so that it could be returned to the still by means of a 
separatory funnel F, at the top of the inlet tube. It was found by 
experiment that the easiest way to distil coal tar was to use at the 
start only one-half of the amount of material for a full charge, and 
by careful heating and by stirring with air to raise the temperature, 
as recorded by the thermometer at T, to about 110° C, and not 
above 120° C. When this point was reached, the rest of the tar for a 
