HIGH-SPEED CENTRIFUGES 



449 



is essentially as shown in the diagram of Figure 156. Figure 157, 

 taken from a review by Beams (1942), demonstrates the effect of 

 the air pressure on the rotor speed for rotors of various designs. 

 Curves A, B, C and D are for a l^/s in. rotor with superstructures of 

 various sizes. The highest speed that Beams had obtained by 1942 

 was almost 1,500,000 R.P.M. with a centrifuge field of almost 

 8,000,000 times gravity; this was accomplished with a 9 mm. rotor 

 driven by hydrogen. The substitution of hydrogen for air at the same 

 pressure produces higher speeds. The usefulness of the gas-driven 

 centrifuge is greatest when accurate temperature control is not 

 required, and a large centrifugal field is desirable over a small radial 

 distance. It has proved valuable for studies of sedimentation 

 within a cell. 



S 6' 



Fig. 156. Diagram of air- 

 driven, air-supported centrifuge. 

 Left: central section through 

 stator cone. Right: section 

 through complete machine. Sta- 

 tor (S) ; rotor (.R). From Beams 

 (1H2) 



3000 



K 2000 



O 



1000 



10 20 30 40 50 60 

 GAGE PRESSURE, lb /m.' 



Fig. 157. Relation between rotor 

 speed and driving air pressure for 

 rotors shown at right of curves. From 

 Beams (19.i£) 



Plastic-Rotor, Air-Driven Centrifuge. This relatively simple 

 instrument (Fig. 158), developed by Stern (1942), consists of an 

 air driven rotor (A) made of a disc of Lucite 0.5 m. thick and 6 in. 

 diameter that has a center axle (D) made from Vie in. drill rod 

 which is supported by Torrington needle bearings (E). 



A top speed of 17,400 R.P.M., at 48 Ib./in.^ air pressure, giving a 

 force of 20,200 times gravity has been obtained. The transparency of 

 the analytical fluid cell has enabled direct observation during the 

 centrifugation, when a stroboscopic light source and a low-power 



