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 



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 



do 



....do 



do .. 



.do 



do 



do 



do 



do 



do 



Yes (1,360° to 1,400° F.).-. 

 No 



Yes (1,350° to 1,400° F.)... 

 No 



. .do 



do 



do 



do 



Yes (1,300° to 1,400° F.)... 

 do 



...do 



do 



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 |-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 tliis 

 occurred, the peep sight was blackened, and the operator had a 

 fraction of a second in which to turn ofi^ 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 



