379 



W 2 to cause both to turn, unless held back in some way. The key of an 

 alarm clock (21) was fastened to a train of gears (20), and these in 

 turn to the stem of roller (IS), so that the rate of motion was held back 

 to a speed governed by the running of the clock, in this case the speed 

 was 30" an hour. The rollers were set in such a way as to cause the 

 paper to pass about |" under the end of the orifice (16) in pipe (15). 

 The strip of paper was marked at the beginning and end of the test, so 

 tbat the exact time when any point on the paper was under the orifice 

 could be determined. Thus a continuous record was kept of the amount 

 of tar in the gas. 



It might be well to state here that all of the tar is not taken out of 

 the gas by this means. The tar particles in the cooled gas are very fine 

 and light, and many of them are cushioned off from the paper, and never 

 touch it to stick. Consequently the tar deposited on the paper does not 

 represent all of the tar content of the coal. On the other hand, the slightest 

 trace of tar in the gas will quickly black the paper, and the deposit is 

 probably very nearly proportional to the entire tar content of the gas. 



6. To prevent re-distillation of tar once deposited, in exit pipe. The 

 remaining problem was that of making sure that no tar could be deposited 

 in pipe (15) at a low temperature and be later re-distilled, to show up 

 on the paper at too high a temperature. To accomplish this a large 

 number of duplicate pipes were made and carefully fitted into the threaded 

 bushing (14). By changing these pipes (15) every five or ten minutes, 

 the effect of such a tendency was quite completely eliminated. 



The coals tested were chosen to represent the different American 

 grades. They were first ground and screened over a mesh of 20 wires 

 per inch and through one of 10 wires per inch. About 315 grams of coal 

 will fill the cartridge, and it was put in in layers J" thick between iron 

 disks. The cartridge was then placed in the middle of the furnace, the 

 thermo couple put in place, and the asbestos packed in against both ends, 

 cutting off the radiation here, and causing the ends and middle, all to 

 keep at the same temperature. A current of 6 amperes was then passed 

 through the resistance wire of the furnace. While the latter was coming 

 up to the temperature where the light oils start to come off, the thermo 

 couples were connected up, the flame placed under the gas pre-heating 

 coil, the gas from the storage tank turned on, the paper rolls connected 

 up to the clock and the clock started. The pipes (15) were cleaned 

 and prepared for immediate use, and the data sheet prepared. As soon as 



