22 THE MECHANISM OF LIFE 



the two freezing points is the required "lowering of the 

 freezing point." 



Cryoscopy is the method most used in biological research 

 to determine molecular concentration. It has, however, some 

 grave defects. It necessitates several cubic centimetres of the 

 liquid under examination. It gives us the constants of the 

 solution at the temperature of freezing, which is far below 

 that of life. Organic liquids are easily altered and are 

 extremelv sensible to minute differences of temperature, 

 cryoscopy therefore gives us no information as to the con- 

 stitution of solutions under normal conditions. It is desirable 

 to have some other method of determining molecular con- 

 centration and the other interdependent constants at the 

 normal temperature of life. A much better method, were it 

 possible, would be the direct determination of the vapour 

 tension of the solutions under normal conditions of temperature 

 and pressure. 



Molecular Lowering of the Freezing Point. — For every 

 substance whose solution is not ionized and therefore does 

 not conduct electricity, the lowering of the freezing point is 

 the same, viz. 1'85° C. for each gramme-molecule of the solute 

 per litre of the solution. 



Determination of the Molecular Concentration. — In order 

 to obtain the molecular concentration of a non-ionizable 

 substance, we have only to determine the lowering of the 

 freezing point. Let A be the lowering of the freezing point 

 of any solution. On dividing it by 1"85 (the lowering of the 

 freezing point for a normal solution), we obtain the number of 

 gramme-molecules in a litre of the solution. It n he the 



number of gramme-molecules per litre, then " = i-rrs- 



1 'tS-> 



Determination of the Osmotic Pressure. — The osmotic 

 pressure P of a solution may be obtained by multiply- 

 ing its molecular concentration n by 22"35 atmospheres. 



P = n x 22-35 = -A. x !>!>!3.5. 

 VS.) 



Determination of Molecular Weight. — The lowering of the 



freezing point also enables us to calculate the molecular 



