W. G. Mixter — Carbon and its Heat of Combustion. 441 



The graphite is probably free from hydrogen as the amount 

 given above is within the limits of error. Three calorimetric 

 tests, using for each about 1-6 gram, gave 7836, 7848 and 

 7810, mean 7831 calories for the heat of combustion of one 

 gram of graphite. 



Second Series of Experiments. 



The carbon for this series was prepared as follows : Acety- 

 lene gas from carbide was passed through a long tube contain- 

 ing solid potassium hydroxide then pumped into the bomb 

 through another tube two meters in length filled with frag- 

 ments of potassium hydroxide. The one to two per cent 

 impurity in the gas was chiefly nitrogen and oxygen. A little 

 phosphureted hydrogen was also present. The gas at an 

 initial pressure of about 10 atmospheres was fired by an elec- 

 tric spark between the neck of the bomb and the valve. The 

 thermal effects for one gram of acetylene in four tests were 

 2063, 2080, 2075 and 2070, mean 2072 calories. This is 32 

 calories higher than the result obtained in the work* which 

 yielded the carbon used in the first series of experiments. 

 The hydrogen gas remaining after the explosion was free from 

 acetylene but contained a little hydrocyanic acid. 



The carbon was tested for hydrogen as follows : Two blank 

 trials of the combustion apparatus were made using about 4 

 liters of oxygen and air in each. The sulphuric-acid absorp- 

 tion tube before the combustion tube gained 1*2 and 1*3 mlgs., 

 and the one at the other end 2*1 and 0'6 mlgs., respectively, in 

 the two tests. Then 2'11 grams of the carbon which had been 

 heated to redness and cooled in a desiccator were placed in the 

 combustion tube, and heated for a time in a current of dry air 

 to drive off any water present. Next the absorption tubes 

 were connected and the combustion was made in the usual way. 

 The anterior tube gained 1*3 mlg. and the one through which 

 the products passed gained 4*2 mlgs. The cause of the 

 increase of the anterior tube was not evident. The oxygen 

 and air used were dried by caustic potash and calcium chloride 

 and then passed through a long U-tube filled with beads 

 drenched with the same sulphuric used in the weighed tubes. 

 It is evident that the gain of 4*2 mlgs., equivalent to 0*02 per 

 cent of hydrogen, may be due to something other than water 

 formed in the combustion of the substance, and we may assume 

 that the carbon was either free from hydrogen or contained 

 too little to be considered in the calorimetric results. 



The carbon was repeatedly digested with a mixture of nitric 

 acid, density 1*57, and potassium chlorate and was finally com- 

 pletely oxidized, leaving, however, a few minute transparent 

 particles. When it was oxidized in other ways similar particles 

 were found. 



* Loe. cit. 



