60 The Conditions of Chemical Change in Gates. [M'y 29, 



1,090 for the velocity of explosion of " dry '' carbonic oxide and 

 oxygen. 



A comparison of the results obtained when dry carbonic oxide and 

 electrolytic gas were exploded in a dried eudiometer with those 

 obtained by Horstmann, and with those obtained by Bunsen,* using a 

 chain of sparks to fire the mixture, revealed the fact that both changes 

 in the shape of the vessel and changes in the initial pressure under 

 which the gases are fired, affect the division of the oxygen. By 

 continually increasing the initial pressure, a pressure is reached where 

 no further increase affects the division of the oxygen. At and above 

 this " critical pressure," the division of the oxygen is also independent 

 of the shape of the vessel. The larger the quantity of oxygen used 

 the lower the critical pressure is found to be. 



When dry mixtures of carbonic oxide and hydrogen in varying 

 proportions are exploded above the " critical pressure " with oxygen 

 insufficient for complete combustion, an equilibrium is established 

 between two opposite chemical changes represented by the equa- 

 tions 



(1) CO + H 2 0=C0. 2 



(2) CO 2 + H 2 =CO + H 2 O. 



So that at the end of the reaction the product of the carbonic oxide 

 and steam molecules is equal to the product of the carbonic acid and 

 hydrogen molecules multiplied by a " coefficient of affinity." This 

 result agrees with Horstmann's conclusion. But Horstmann con- 

 siders the coefficient to vary with the relative mass of oxygen 

 taken. 



A small difference in the initial temperature at which the gases are 

 fired makes a considerable difference in the products of the reaction. 

 This difference is due to the condensation of steam on the sides of 

 the vessel during the explosion, and its consequent removal from the 

 sphere of action during the chemical change. When the gases are 

 exploded at a temperature sufficiently high to prevent any conden- 

 sation of steam during the progress of the reaction, the "coefficient 

 of affinity" is found to be constant whatever the quantity of 

 oxygen used, provided that the hydrogen is more than double the 

 oxygen. 



The presence of an inert gas, such as nitrogen, by diminishing the 

 intensity of the reaction, favours the formation of carbonic acid in 

 preference to steam. When the hydrogen is less than double the 

 oxygen the excess of oxygen cannot react with any of the three other 

 gases present carbonic oxide, carbonic acid, and steam but has to 

 wait until an equal volume of steam is reduced to hydrogen by the 



" Gasoin. Meth.," 2te Auflage. 



