CATALYSIS 5 



of the copperas solution quickly changes to yellow, owing to 

 the formation of ferric sulphate, according to the following 

 equation : — 



2FeS04 + HaSO.! + NO^ = Fe2(S04)3 + NO + H^O 



The NO combines with the oxygen in the air present to 

 form NO3 and so continues the reaction. This process has 

 been made the subject of a patent, and is used to prepare ferric 

 salts on the large scale for the purpose of precipitating sewage. 



Another important case of catalytic action is the action 

 of manganese dioxide on the decomposition of potassium 

 chlorate by heat ; the temperature at which oxygen is evolved 

 from potassium chlorate on heating is very much reduced by 

 the addition of a comparatively small amount of manganese 

 dioxide. In this case also it has been shown by McLeod, the 

 present writer and others, that the action of the manganese 

 dioxide is probably due to the formation and decomposition 

 of intermediate substances. 



The reactions which take place in hving matter come, in 

 many cases, under the order of catalytic reactions. The 

 nature of the catalyst is one of the problems for consideration. 

 These catalysts occurring in Hving matter are known as 

 enzymes or ferments, and their varying effects form the chief 

 subject-matter of this book. 



Many of the reactions which take place in nature can be 

 imitated in the laboratory by fairly simple methods ; thus, 

 e.g., cane sugar is easily converted into grape sugar by warming 

 tor some time with dilute acid, according to the following 

 equation : — 



C12H23OU + H2O = 2C„Hi20o 



Ethereal salts or esters of the simpler fatty acids, such as, 

 e.g., ethyl acetate, can be broken up by warming with dilute 

 acid or alkali, yielding alcohol and acetic acid. Such a 

 reaction does not proceed to completeness under ordinary 



