OXIDATION-REDUCTION POTENTIALS 1 !) 



The phosphate buffers make use of the second and 

 third hydrogen atoms as the acids with the corresponding 

 salts so that phosphate buffer solutions can be made 

 covering a wide range of pK values. 



So called " Universal buffer mixtures " consist of a 

 mixture of acids, with pK values covering a wide range, 

 to which the calculated amounts of alkali are added to 

 give solutions buffered at the required pK. Such a mixture 

 covering the range pH 2 to pK 12 comprises phosphoric 

 acid, citric acid, boric acid and hydrochloric acid. The 

 same range is also covered by the mixture boric acid, 

 citric acid, jDotassium di hydrogen phos2)hate and veronal. 



Proteins and amino -acids have a considerable buffering 

 effect since they may function as weak acids or weak 

 bases in virtue of their carboxyl and amino groups, 

 according to the conditions. 



Oxidation-Reduction Potentials 



It will be seen later that oxidation and reduction play an 

 extremely important part in the respiratory and metabolic 

 processes of micro-organisms. In fact it is not too much 

 to say that their whole existence depends on such reactions, 

 which not only supply the energy for their gro\\i:h and 

 reproduction but are also involved in the production of 

 the intermediate compounds or "building stones " out of 

 which are synthesised all the complex proteins, fats, 

 carboh3^drates, pigments, and so on, making up the body 

 of the organism. As a result of the introduction of means 

 of measuring the intensity of the oxidising or reducing 

 power of substances in recent years the study of oxidation- 

 reduction systems in connection with bacterial metabolism, 

 gro\^i;h and development has increased rapidly and 

 afforded considerable knowledge of previously obscure 

 processes . 



Our first ideas of oxidation naturally involve the 

 addition of oxygen to an atom or a compound, a t}^:)ical 



