586 PROCEEDINGS OF THE AMERICAN ACADEMY. 



(Nos. 19, 20, and 21) were made in the usual way with the bomb origi- 

 nally filled with air, and the average value for the heat of combustion 

 of benzol in this series was the same as that obtained in the first series. 

 Again three combustions (Nos. 22, 23, and 28) were made with the air 

 removed from the bomb before the oxygen was run in, and again results 

 were obtained more than 0.3 per cent greater than the results of the 

 combustions in which the bomb was filled with air at the beginning. 

 At the same time, in those cases in which the bomb was exhausted 

 the amount of nitric acid formed during a combustion did not appreci- 

 ably diminish, hence it was evident that the oxygen in use must 

 contain nitrogen. 



After due consideration of these results the logical conclusion seemed 

 to be that the presence of an inert gas such as nitrogen in some way 

 or other interfered with the complete burning of the benzol, and there- 

 fore lowered the heat of combustion. In order to test this hypothesis 

 further, more combustions were made in the presence of still greater 

 concentrations of nitrogen, under which conditions the heat of com- 

 bustion should be still more diminished. To accomplish this, air was 

 forced into the bomb by means of an ordinary bicycle-pump, and the 

 pressure of the air forced in was measured on the pressure-gauge. 

 Oxygen was then run in until the pressure inside the bomb was 35 

 atmospheres. Since the amount of nitrogen in the oxygen had been 

 determined, it was a simple matter to calculate the approximate 

 amount of nitrogen in the bomb. The results of the combustions 

 made under these conditions agreed with the hypothesis, and while 

 the relation was not a simple ratio, yet the results showed clearly 

 beyond a doubt that the greater the concentration of nitrogen the 

 lower the heat of combustion. This effect of nitrogen in combustion 

 suggests the retarding influence of oxygen on the rate of formation 

 of hydrochloric acid when hydrogen and chlorine are exposed to the 

 light,^ and numerous similar phenomena, sometimes classified under 

 the general head of negative catalysis. 



In presenting these results, a typical determination is given in detail, 

 in order to illustrate further the method of calorimetry ; afterwards a 

 table giving all the later results with benzol is recorded. 



Determination No. 23, 



Weight of benzol (A), 0.5840 gram. 



Weight of sugar (B), 0.2073 gram. 



Air was exhausted from the bomb before admitting oxygen. 



The bomb was immersed in the calorimeter at 11.25 o'clock, and 

 the temperature of jacket and cover were adjusted at 11.30 o'clock. 



8 Bunsen and Roscoe, Pogg. Ann., 96 (1855) ; Phil. Trans., 147, 389 (1857) 



