377 



tapped for the \" pipe (12), through which the gas from the coal could 

 pass out. The other was drilled and tapped for a thermometer well (8) 

 aud i" pipe (11). The body of coal heated each time was therefore 2|" 

 in diameter, aud it was necessary to have all the particles of coal in 

 this mass at the same temperature. As coal is a very poor conductor of 

 heat, it was decided to place iron disks (10) J" apart throughout the entire 

 length of the cartridge. These disks were large enough to touch the iron 

 cartridge all around, thus taking on its temperature, and were drilled 

 full of small holes to allow the gas to pass through them. As they were 

 i" apart, the heat had to be conducted through only I" of coal. This fact, 

 together with the very slow rate of heating employed, led us to expect the 

 temperature throughout to be the same, within very close limits. The 

 temperature was read at the very center of the coal body, by means of a 

 thermo couple, the end of which extended down to and touched the end 

 of the thermometer well (8). 



3. Means of measuring the temperature. The thermo couples used 

 were made of iron and nichrome wires welded together in an electric 

 arc. The couples were used with a Brown millivolt meter, with a resist- 

 ance of 85 ohms. It was carefully calibrated and checked at the time the 

 experiments were completed. The couples were correct to within 10° C. 

 throughout the range of temperatures here reported. The couples were 

 left in place throughout each entire test, and the temperature readings 

 made whenever desired. 



4. To keep the gases sioept out as formed. To sweep the gases out as 

 they were formed gas free from tar was forced into the cartridge under 

 pressure, through the \" pipe (11), and allowed to pass out through (12) 

 in a constant stream. The pressure of this gas inside the cartridge was 

 measured by a mercury manometer, and was kept at about 2¥' of mer- 

 cury. This gas could not be allowed to contain any 2 , as it might then 

 burn the coal or tar vapors at the higher temperatures, so air with the 

 2 burned out was used. The arrangement of the apparatus as used is 

 shown in Fig. 2. The air was burned in a small furnace made of a piece 

 of 6" pipe about 2' 6" long. This pipe had grates at the bottom and 

 a coupling and plug at the top. The coupling was drilled and tapped I" 

 pipe size on one side, and connected to a large coil of \" pipe which rested 

 in a tank of cold water. The small furnace thus constructed was filled 

 with an anthracite fire and the plug at the top put in. The air pump 

 then pumped air through the furnace and cooling coil and compressed 



