W. G. Mixter — ffeat of Combustion of Hydrogen. 219 



The bomb was then filled with hydrogen and exhausted to 

 a pressure of 15 to 20™"^ and the process was repeated a num- 

 ber of times. This method of filling the bomb was adopted 

 with the idea that there was less danger of air leaking into the 

 bomb than if the exhaustion was made more nearly complete 

 by long pumping with a mercury pump. The close agreement 

 between the calculated and observed weight of the hydrogen 

 shows that the errors from impurity of the gas were negligible 

 except in four experiments of the first series. The apparatus 

 used in filling the bomb in this series was similar to the one 

 described with the exception that some rubber tubing was used 

 in the connections. After the final filling of the bomb with 

 hydrogen the mercury was removed from S so that the gas in 

 the bomb which was under more than atmospheric pressure 

 might escape through the long small tubing until it attained 

 the pressure of the atmosphere and without danger of air dif- 

 fusing into the bomb. The temperature, pressure and weight 

 of the gas were noted. The hydrogen was weighed in order 

 to have evidence of its purity but the mass calculated from the 

 volume was used in the calculation of a calorimetric result. 

 The oxygen required was made from potassium chlorate, and 

 was passed through a cylinder filled with sticks of potassium 

 hydroxide and condensed in an iron flask containing solid 

 potassium hydroxide. It was free from compounds of carbon 

 and contained 2*7 per cent of nitrogen. With this amount of 

 nitrogen present the quantity of nitric acid which was formed 

 by an explosion was too small to be taken into account. The 

 bomb was rinsed after an explosion with about 100"^° of water. 

 The wash water was neutral to ordinary litmus paper, gave a 

 slight turbidity on addition of hydrochloric acid, and contained 

 only a milligram of silver. The oxygen was passed by means 

 of a tube 2""°^ in diameter into the bomb and the valve of the 

 latter was closed when the gauge indicated rather more than 

 half an atmosphere. There was, therefore, no danger of loss 

 of hydrogen by diffusion. The quantity of oxygen in the 

 bomb was also found by weighing. 



To Dr. H. A. Bumstead of the Physical Laboratory the 

 writer is indebted for the following method of reducing the 

 results. 



The general formula for reducing the heat of combination, 

 found under the condition of constant volume, and between 

 the temperatures t^ and t^ to that found at 0° and under con- 

 stant pressure, is easily obtained by imagining the mixed gases 

 to be carried through two different processes from the same 

 initial state to the same final state, and equating the losses of 

 energy in the two processes. 



Am. Jour. Sci.— Fourth Series, Vol. XYI. No. 9.^. — September. 1903. 

 15 



