CATALYSIS AND CATALYSTS 203 



binations of hydrogen effected by the agency of a catalyst date 

 from the extreme end of the last century, and have excited not 

 only great interest among those occupied in scientific chemistry, 

 but have led to unexpected applications to industrial purposes 

 which already have assumed a position of great practical im- 

 portance. 



These researches seem to have originated in attempts, known 

 to have been made by Moissan, to contrive the direct union of 

 acetylene with certain metals such as copper, nickel, and iron. 

 The expected fixation did not take place, but Sabatier found 

 that ethylene, as well as acetylene, when directed on finely 

 divided metals at a temperature of only 300 C. produces in- 

 candescence with a deposit of carbon, the escaping gas consisting 

 of hydrogen mixed with ethane. This seemed to indicate that 

 hydrogen had been added to the elements of the ethylene, and by 

 further experiments it was found that a mixture of ethylene and 

 hydrogen passing through a column of reduced nickel is changed 

 into ethane by combination of the two gases : C 2 H 4 +H 2 = C 2 H 6 . 



In association with M. Senderens further research enabled the 

 enquirers to generalise this result. Even at common tempera- 

 tures acetylene mixed with excess of hydrogen, in contact with 

 the metal, is completely converted into ethane, without destruc- 

 tion of any portion of the hydrocarbon and without formation 

 of secondary products. 



These experiments carried out in 1899 showed that nickel 

 freshly reduced from its oxide possesses this catalytic power in 

 relation to hydrogen in a peculiar degree. Reduced cobalt, iron, 

 and copper, as well as spongy platinum partake of this property 

 more or less. 



Various modifications of the process have since been devised, 

 especially with the object of operating on materials in the state 

 of liquid, without resorting to the process of converting into 

 vapour or gas. At the temperatures necessary for this purpose 

 many carbon compounds are destroyed or seriously altered in 

 composition. These modifications are in many cases successful, 

 but the interaction takes place much more slowly. 



As to the chemical changes which are brought about by the 

 process of hydrogenation they may be ranged into several 

 classes. When oxygen is present water is formed in some cases, 

 while in others hydrogen is simply added on. In other cases the 

 molecule is broken up as when benzene, C 6 H 6 , is converted by 



