196 CHEMICAL DISCOVERY AND INVENTION 



while the whole is kept cool. The hydroxylamine crystallises 

 from the liquid in the form of sulphate and the yield is almost 

 theoretical. 



By the use of a cathode cell and appropriate current density, 

 temperature, and dilution many organic compounds may be 

 similarly produced with results, as to yield, which in many cases 

 are superior to the older methods of reduction by means of 

 sodium, sodium amalgam, or zinc dust and acid. 



CHAPTER XI 



CATALYSIS AND CATALYSTS 



THESE look like very hard words, but as catalyst is derived from 

 the Greek, which merely means an agent which unloosens or sets 

 free something else, they can be regarded as reasonable in their 

 application, and not, as appears in some other cases, a device 

 for concealing ignorance. 



An example will make the matter clear. Oxygen mixed with 

 twice its volume of hydrogen forms a mixture which is well 

 known to explode on approach of a flame or an electric spark, or 

 when heated strongly enough in any other way. This mixture 

 of gases may be kept indefinitely in a closed vessel in the dark 

 or in sunlight without the production of water or any other sign 

 of chemical combination. If, however, a perfectly clean piece 

 of platinum foil is introduced into the mixture combination 

 between the oxygen and hydrogen immediately begins, and often 

 proceeds so rapidly that the metal becomes red hot and ulti- 

 mately the residual gas explodes. But when the action is all 

 over the platinum betrays no sign of having had anything to do 

 with the matter. It is unaltered in weight and appearance and, 

 if unsoiled by handling or otherwise, it retains the peculiar 

 catalytic property which it has just manifested. 



The facts just related were discovered so long ago as 1817 by 

 Sir Humphry Davy, who, with the aid of a spiral of platinum 

 wire suspended in a glass containing a little alcohol or ether, 

 demonstrated the union of the vapours with the oxygen of the 

 air on the surface of the metal, producing what he called his 

 " lamp without flame." Many observations of the same kind 



