74 E. G. P I C K E L S 



serve as window receptacles also), a threaded Duralumin barrel or casing, and 

 a screw ring of the same material. The centerpiece, which is generally ano- 

 dized for chemical resistance, is provided with a sector-shaped slot, 15 mm. 

 long (in direction of centrifugal force) and a few millimeters wide, that ac- 

 commodates the fluid. Surrounding the central slotted section are concentric 

 grooves to promote a fluid-tight seal against thin washers of plastic placed 

 between the centerpiece and the quartz windows. The assembled cell is filled 

 with the aid of a hypodermic syringe at the narrow end of the slot through 

 a small hole, which is then sealed with a thin rubber gasket and a small screw 

 plug fitting a threaded hole in the barrel. Centerpieces with fluid column 

 thicknesses (axially) up to more than 12 mm. may be used. Light passing 

 through a hole in the counterbalance at a radial distance greater than that 

 corresponding to the bottom of the cell slot furnishes a reference for the light 

 intensity or the distance from the axis of rotation. 



The rotor spins about a vertical axis within an evacuated chamber, seen 

 in the lowered, opened position in Figure 3. The double-walled steel cylinder 

 and thick steel end plates, along with a heavy locking device and the steel 

 walls of a surrounding barricade, furnish protection to the operator and the 

 equipment in the event of rotor failure. A third, inner cylinder, which im- 

 mediately surrounds the rotor, can be refrigerated for work at reduced tem- 

 peratures. Pressures well below 1 ^ of mercury are obtained in the vacuum 

 chamber by means of an oil diffusion pump backed up by a mechanical 

 vacuum pump. The rotor is attached by a coupling device to a spring steel 

 shaft 0.1 in. in diameter, which passes through a vacuum-tight oil gland to the 

 driving mechanism above the vacuum chamber. Suspension of the rotor by 

 means of a flexible shaft makes the rotor self-balancing and permits an off- 

 balance of several grams at the cell without excessive vibration or other ill 

 effects. The arrangement is an advantage in the event of cell leakage and 

 also avoids the necessity of extreme accuracy in balancing the rotor. There 

 is an appropriate damping device to prevent swinging or precession of the 

 rotor and a collecting system for the few milliliters of oil that escape through 

 the sealing gland during a run. The temperature of the rotor can be meas- 

 ured with a thermocouple attached to the rotor before and after a run, and 

 also during a run by a radiation couple located near the coupling device. At 

 a speed of 60,000 r.p.m., the rise in temperature of the rotor is of the order of 

 1°C. per hour if the surroundings are at a temperature near that of the rotor. 

 By lowering the temperature of the refrigerated cylinder about 10 or 15°C. 

 below that of the rotor, one can keep the rotor temperature nearly constant 

 indefinitely. 



The driving mechanism consists of a series-wound, brush type electric 

 motor (115 v.), a high speed gear train, and a system of specially designed 

 mechanical bearings. The motor, cooled by circulation of both air and 

 water, develops 1.5 horsepower and will get the centrifuge to full speed within 

 seven minutes. Deceleration of the rotor to rest is accomplished in a com- 



