Moisture Content of Some Typical Coals. 179 



some water vapor. In a few minutes, however, the water 

 vapor was liberated more slowly than condensation took 

 place and from this point oh only the gas pressures were 

 observed. This first part of the curve may be obtained 

 by a short extrapolation, but (this first few minutes 

 of the curves) is not important for our purposes. We 

 secured a series of pressure readings at convenient 

 intervals, but the volume of the apparatus and the tem- 

 peratures were still necessary for calculating the volume 

 of gas corresponding to each time interval. This seemed 

 to be a difficult problem in view of the wide difference of 

 temperature in various parts of the apparatus. We 

 were able however to get a most satisfactory "tempera- 

 ture-volume" factor to combine with our pressure read- 

 ings. After the pressure readings had been made, the 

 gas was pumped out of the apparatus and connection 

 was made with the top of the burette of the apparatus 

 represented in fig. 4. Gas was now allowed to fill the 

 apparatus from the burette until the pressure in the 

 apparatus and burette was atmospheric, the various 

 parts of the apparatus were maintained at the same tem- 

 peratures as in the experiment. The burette readings 

 thus gave the volume of gas at atmospheric pressure and 

 room temperature which filled the apparatus at its tem- 

 peratures under the pressure of the atmosphere. Obvi- 

 ously the burette volume and temperature may be used 

 in our calculations with each observed pressure reading 

 and thus we were able to calculate the exact volume of 

 gas present at each of the time intervals. . It was of 

 course necessary to admit only dried gases into the appa- 

 ratus and it was also necessary to use an indifferent gas 

 since dehydrated coals at the temperatures employed 

 absorb oxygen very rapidly. We used methane, hydro- 

 gen or coal gas, which was forced in through the leveling 

 tube and up through the burette and . out through the 

 three-way cock of the apparatus, thus thoroughly drying 

 these tubes. The burette apparatus was designed so 

 that concentrated sulphuric acid might be used in it and 

 thus insured a perfect dryness for the apparatus and 

 gases used. With the aid of the rubber mouthpiece E 

 and the cock F, it was possible to control the acid in the 

 burette apparatus and make all readings with the gas 

 pressure in the burette atmospheric. When the alumin- 

 ium disks, fig. 2, properly stopped convection currents in 



