the Halogens, Nitrogen, Sulphur and Oxygen. 377 



the temperature of the room, which was constant, was 1*8 0C 

 greater than before the combustion. 



Experiment %. — 0-0337 gram of same charcoal as used in 1, 

 gave the same results, except that the volume of gas increased 

 2-4 cc . 



Experiment 3. — Another lot of hard burned charcoal was 

 tried in gas dried for a day. Three times the coal failed to 

 burn after it had been heated at one point to incandescence, 

 burning, however, brilliantly when ignited by prolonged 

 heating. 



Experiment J^. — The charcoal from the same piece as used 

 in 3, did not burn when first heated to redness at one point 

 but when heated a second time it burned well. 



Experiment 5. — Dense sugar charcoal containing 0126 per 

 cent of hydrogen ignited promptly when the wire cone hold- 

 ing it was heated, and burned brilliantly and completely in 

 oxygen which had been in contact with phosphorus pentoxide 

 thirteen days. 



For the remaining experiments with the Hoffmann appara- 

 tus the sugar charcoal described on page 366 was used. It 

 contained - 07 per cent of hydrogen and 0*17 per cent of ash. 

 The amount weighed off for each trial was - 04 gram, which 

 was somewhat reduced by heating as already described. The 

 gas was allowed to dry for two days in each case. 



Experiment 6. — The charcoal did not burn after it was 

 heated to faint redness, but when heated hotter it continued 

 to burn after the current from the battery was broken. The 

 volume of the gas increased 15 c0 . 



Experiment 7.— The charcoal after it was first ignited burned 

 a few seconds. Ignited a second time it partly burned, and .it 

 did not burn completely until it was heated intensely. The 

 volume of the gas was 2 CC greater than before the combustion. 



Experiment 8. — The charcoal burned completely after the 

 battery current was broken. In this and the following tests 

 the apparatus stood in a cylinder of water having the tempera- 

 ture of the room. The pressure of the gas when it had at- 

 tained the temperature of the water was 2 - 4 mm of mercury 

 greater than before the combustion. 



Experiment 9. — The result was the same as in 8, except that 

 the pressure increased 2 ram . 



Experiment 10. — The charcoal was heated gradually until it 

 was ignited. . The pressure increased 3 mm . 



Experiment 11 — The charcoal ceased to burn after the first 

 heating by the hot wire and when ignited again it burned com- 

 pletely. The pressure increased 2 mm . 



The increased volume of gas after a combustion can only be 

 explained on the assumption that some carbonic oxide was 



