PHYSICAL PROPERTIES OF NUCLEIC ACIDS 



471 



0-4 



06 



O O-l 0-2 0-3 



Concentration per cent 



Fig. 12. The variation of sedimentation constant with concentration of sodium 

 deoxypentose nucleate. 



3 data of Cecil and Ogston^" 

 O data of Atlas and Stern" 

 O data of Tennent and Vilbrandt*' 

 • data of Kahler.6? 



The diffusion coefficient also varies with the concentration and although 

 the values obtained by extrapolation to infinite dilution by Kahler^- and 

 Cecil and Ogston^"-^^ are in fairly close agreement, the diffusion coefficient 

 was found to vary with concentration in opposite senses by these two 

 groups of observers. Kahler's results show a marked increase of the diffusion 

 coefficient with concentration, while those of Cecil and Ogston show an 

 equally marked decrease. Although the experimental technique was differ- 

 ent in the two cases — ^Cecil and Ogston used the Gouy method and Kahler 

 the more common Neurath cell with the Lamm scale or Longsw orth scan- 

 ning optical methods — it is clearly evide;it that further experimental work 

 is desirable to determine the true concentration dependence. The determi- 

 nation of the diffusion coefficient is, furthermore, made more difficult, 

 since owing to the concentration dependence of the diffusion coefficient, a 

 skewed boundary is obtained (Fig. 14) and there may also be an apparent 

 movement of the boundary.^* The value of the diffusion coefficient ob- 



" J. A. V. Butler and D. W. F. James, Nature 167, 844 (1951). 



