54 PHYSICAL CHEMISTRY IN BIOLOGY. 



equilibrium is present or from the velocity coefficient k\ and k% as deter- 

 mined in a manner given below. 



In the above-mentioned transformation of alcohol and acetic acid 

 these two bodies are simultaneously used up. The reaction is therefore 

 called bimolecular, and a reaction is called mono-, bi-, tri-, etc., molecular 

 according to che number of the kinds of molecules which diminish their 

 concentration thereby. 1 



BERZELius 2 found that certain bodies by their mere presence, and 

 not by their affinity, have the power of awakening the dormant" 

 affinity at a certain temperature. These phenomena were called 

 catalytic by BERZELIUS. 



According to OSTWALD 3 catalysis is the acceleration (or retardation) 

 of a slow-proceeding chemical change by the presence of a foreign body. 

 That body which influences a reaction in this manner is called a catalyst. 

 It does not undergo any appreciable change by the reaction. 



Catalytic reactions have been studied, especially by WiLHELMY, 4 

 VAN'T HoFF, 5 OSTWALD, G ARRHENIUS 7 and BREDIG. S Of all other sub- 

 stances the acids and alkalies seem to act most catalytic. A well-known 

 example is the inversion of cane sugar by means of acid. This reac- 

 tion is monomolecular because only the cane sugar is consumed. -If 

 the concentration of the cane-sugar at the beginning is C moles, and if 

 x moles are transformed in t time, then at that time there are (Cx) 

 moles remaining. If dx indicates the quantity which is transformed 



in dt time, then the reaction velocity is -j-. According to the law 



at 



of mass action this is at every moment proportional to the concentration 

 of the decomposing substance, or 



ar*-(c-*> a) 



For practical use this equation is integrated into the following : 



og. (2) 



1 It is assumed here that of every kind of molecule one molecule of each takes 

 part in the reaction. 



2 Berzelius, Arsberattelse om framstegen i Fysik och Kemi., 13, p. 245, 1836. 



3 Lehrb. d. allg. chem. 2. Aufl. II., 1, 515. 



4 Poggendorff's Ann., 81, 413, 1850. 



5 Etudes de dynam. chim., 1884. 



8 Lehrb. d. allg. Chem., 2. Auf. II, 2, 199. 



7 Zeitschr. f. physik. Chem., 4, 228, 1889. 



8 Anorganische Fermente, 1901; Bioch. Zeitschr., 6, 283, 1907. 



