i66 



PHYSIOLOGY OF MICROORGANISMS 



distributed over the top of the table. These supported a thick glass 

 plate on which several blocks of paraffine for each piece of apparatus 

 were placed. Thus it was possible to obtain a perfect insulation. 



In preparing the different parts of the apparatus extreme care should 

 be exercised to obtain an accurate result. The method for the prepara- 

 tion of the normal element, calomel electrode, gas cell, and also calibra- 

 tion of the bridge wire, etc., is described in detail in Findlay's " Practical 



FIG. 102. Apparatus employed in determination of H-ion concentration. 



DESCRIPTION OF DIAGRAM 



LI Lippmann's capillarimeter. 83 Two-way switch. 



L 2 Tungsten lamp. C Calomel electrode. 



A Accumulator. K Concentrated KC1 cup. 



N Western normal element. G Gas cell. 



Si Switch with quick short circuiting key. B Bridge. 



82 Three-way switch. P Thick glass plate. 



Physical Chemistry." Every contact should be carefully made, so that 

 accurate readings can be obtained. It is worthy of mention that the 

 diffusion potential between n/io KC1 calomel electrode and the solution 

 to be tested is reduced by interposing the saturated solution of KC1 as it 

 is indicated by K on the diagram. For the standardization of the elec- 

 trode it was first platinized with general precaution; then the hydrogen 

 ion concentration of the mixed solution (7 c.c. of m/i5 KH 2 PO 4 , 3 c.c. of 



