38 A. Killen Macbeth on 



filtration of coloured solutions throuf^h layers of charcoal. This 

 is purely a surface effect, and when it is recollected how large a 

 surface is presented by the finely divided or colloidal metals, the 

 probability of adsorption as a factor in catalysis is apparent. It 

 has been calculated that if a sphere of gold with a radius of 

 1 m/m (about the size of a lead shot) were broken down into the 

 colloidal state the particles would present a surface of nearly 

 1,000 sq. feet. On the adsorption view the reacting substances 

 are condensed on the surface of the catalyst, and so are brought 

 more closely together. There is therefore a greater chance of 

 their reacting : and so the velocity of the reaction is increased. 



These are the outstanding views that have been presented 

 to account for the action of catalysts in speeding-up chemical re- 

 actions. Whether they are a correct representation of the state 

 of affairs matters but little, as the application of catalysis to 

 commercial operations is fortunately not dependent on such 

 explanations. So without further enquiry we may proceed to 

 examine some of the outstanding uses of catalysts in industrial 

 processes. 



Part II. 

 The Catalysis of Commercial Chemical Processes. 

 In introducing the second part of the subject, we may first 

 look at a particular case illustrating the effective application of 

 catalysis to a commercial problem. In the manufacture of 

 carbonate of soda (washing soda) from common salt, two great 

 difficulties were encountered in connection with bye-products 

 formed during the process. In the first place large amounts of 

 hydrochloric acid were produced during the course of manufac- 

 ture, and as there was no great demand for this, it was allowed 

 to escape into the air through tall chimneys. The acid which 

 thus escaped was carried down by rains and had a very 

 harmful effect on the vegetation of the surrounding country. 

 This and other public inconveniences gave rise to widespread 

 grievance, and the manufacturers were compelled to dispose of 



