98 



E. G. PICKELS 



desiccation {29) ; formation of micelles by detergents {30) ; ultracentrifugal 

 homogeneity of carbohydrates {31); ultracentrifugal behavior of cellulose 

 {50). 



F. PREPARATIVE CENTRIFUGATION AND QUANTITA- 

 TIVE METHODS BASED ON SAMPLING 



1. Preparative Centrifugation 



Most high speed (above 10,000 r.p.m.) preparative centrifuges 

 suitable for the concentration and purification of particles in the size 



Fig. 8. Six-inch preparative rotor of Duralumin for routine operation at 

 50,000 r.p.m. in the vacuum ultracentrifuge. (Courtesy Specialized Instruments 

 Corporation.) 



range below 100 m are of either the inclined tube type {62,63,76) or the 

 continuous flow type {91), and are operated in a vacuum or under 

 atmospheric conditions depending on the required speed, capacity, 

 operating temperature, and degree of freedom from convective dis- 

 turbances. One of the interchangeable preparative rotors used with 

 the vacuum ultracentrifuge already described is shown in Figure 8. 

 In such rotors the tube holes are usually arranged at some angle be- 

 tween 10 and 45° to the axis of rotation, and the rotor is machined 



