SECTION IX. 



ENZYMES. 



It has long been known to chemists that the velocity of chemi- 

 cal reactions could, in many cases, be increased by the presence 

 of relatively small quantities of certain substances which do not 

 appear to take any immediate part in the reaction. 



This is well illustrated by the familiar example of the effect 

 of a small quantity of manganese dioxide in bringing about the 

 liberation of oxygen from potassium chlorate at a temperature 

 much lower than would be possible by heating this substance 

 alone. 



Other examples of the accelerating influence of foreign 

 substances on the velocity of reactions are to be found in the 

 use of cuprous chloride in Deacon's chlorine process, and of 

 spongy platinum, either in the manufacture of sulphuric acid by 

 the contact process, or for effecting the explosive combination 

 of hydrogen and oxygen. 



Similarly, the hydrolysis of cane sugar according to the 

 equation — 



Ci^H^Ai + HP = aC.Hi^Os 



takes place very slowly in neutral aqueous solutions, but 

 may be greatly accelerated by warming the solution with a little 

 mineral acid. 



A feature common to all the above reactions is the fact that 

 the substance which produces the accelerating influence is un- 

 altered by the reaction, and can usually be recovered from the 

 reaction-product unchanged in quality and quantity. 



Substances which have this remarkable property of being 

 able in some way to influence the velocity of a reaction, 

 without apparently undergoing any change themselves, and 

 which act in quantities which bear no particular relation to the 

 weights of the reacting substances, are called catalytic agents. 



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