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99 



CATALYSIS IN THE INORGANIC FIELD 



by yeast, the yeast plant produces the catalyst, or enzym, as it is more fre- 

 quently called. The Arabs are said to have known the catalytic action of 

 sulfuric acid in the conversion of alcohol into ether. The alchemists knew that 

 niter hastens the purification of gold by cupellation, and that sulfur will pro- 

 duce sulfuric acid if saltpeter is first mixed with it. Otherwise, sulfur burns 

 mainly to sulfur dioxid. 



In 1836 Berzelius, the famous Swedish chemist, compiled all cases known 

 in which, by the presence of a foreign body, a chemical reaction is hastened 

 without the foreign body itself being changed. These foreign bodies thus 

 acting Berzelius named "catalysts." This classification included all those ac- 

 tions that Mitscherlich had discussed but a short time before. In dealing 

 with the process of making ether from alcohol Mitscherlich named the sulfuric 

 acid a "contact substance," expressing thus the thought that the sulfuric acid 

 was active merely and solely by its presence and its contact. A recent defini- 

 tion of a catalyst or contact substance includes substances that affect the 

 velocity of a chemical reaction without appearing in the final products. 



" In sharp contrast with chemical reactions that, when not catalyzed, 

 proceed at so low a rate as to produce less than noticeable amounts of products, 

 stand the reactions that are so rapid as to be practically instantaneous. Re- 

 actions between ions are, for example, practically instantaneous. Of course, 

 catalysis is not concerned with such reactions. 



It is not strictly true that a catalyst is found to be unchanged at the end of 

 a catalyzed reaction. It is correct to say that the final products are the same 

 as they would have been had the catalyst been absent. The catalyst may be 

 rather unmistakably changed, not in amount but in physical state. Thus the 

 crystalline manganese dioxid used to generate oxygen from potassium chlorate 

 becomes a fine powder, and changes in physical state are known to occur in 

 iron oxid and in platinum used as catalysts in other systems. The amount of 

 the catalyst, no matter how small, seems to remain unchanged. Catalysts 

 themselves may be accelerated or restrained in their rapidity of action. Two 

 catalysts usually have a greater joint effect than either would have singly. 

 "Promoters" that increase the activity of catalysts are also known. Some 

 substances so completely obstruct the action of catalysts that they have been 

 called "poisons." Enzyms and toxins have their poisons and antitoxins, and 

 the analogy to them is quite close, even in the case of metallic catalysts. 



Some catalysts seem specific for a given reaction, but many catalysts are 



