116 WHAT IS LIFE 



direct sunlight or other radiation, is not a factor at 

 this moment. 



With these ehminations the inquiry is reduced to 

 the utmost possible simplicity. 



IV. WHAT IS MEANT BY "CONDITION OF A 

 CRITICAL CONCENTRATION OF lONS" 



Primarily it is a condition that perhaps is possible 

 only in a liquid solution (liquid: slight compressibil- 

 ity, the molecules presumably in contact), and that 

 probably cannot obtain in a gas or a solid. 



Further, since hydrogen ions are needed, and free 

 hydrogen ions are found only when acids are dis- 

 solved and dissociated in water (Nernst^), water is 

 postulated. 



Hydrogen ion concentration has various (definite) 

 values according to the extent to which dissociation 

 takes place. "Ionic concentration," of course, means 

 the quantity of gram-atoms of an ion per unit volume 

 in a solution. 



A critical condition, the isoelectric point, of the 

 colloidal state is that which results from the intro- 

 duction of a small quantity of an electrolyte into the 

 colloidal solution, when electrolytic movement is 

 suspended and precipitation or coagulation of the 

 particles occurs. This critical condition, needless to 

 say, is entirely unrelated to the critical condition 



1 Theoretische Chemie (edition of 1926), 637. 



