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Science: Centrifuge

3 minute read

Cream separators are centrifuges. To bacteriologists who use more delicate centrifuges to whirl germs out of solutions, the name Svedberg is as familiar as the name De Laval is to dairymen. Lately at Sweden’s University of Upsala, shy, black-eyed, Nobel Prizewinner Dr. Theodor Svedberg, 50, perfected two new rotors in which at normal operating speed a dime would press against the wall with a force of half a ton. One rotor he kept. The other he sent to the du Pont research laboratories at Wilmington, Del. There last week Dr. Elmer Otto Kraemer put the machine through its paces for a group of scientists and newshawks.

Festooned with a maze of cables, wires, tanks, cylinders, hand-wheels, steel support frames bolted to the ceiling, a control board studded with dials, the underground laboratory looked something like the inside of a submarine. The Svedberg centrifuge’s 7-in. disk rotates at 60,000 r.p.m., has a peripheral speed of about 24 miles a minute, one-third greater than that of Earth at the Equator. Particles whirled at that rate are subjected to a force 250,000 times that of gravity. In short spurts the centrifuge can rotate up to 160,000 r.p.m., exaggerating gravity 1,100,000 times. If this speed were maintained more than a few seconds the rotor would fly into smithereens. To prevent injury or death in case of such a mishap the 20-lb. rotor is girt by an 800-lb. steel shell, 5 in. thick.

To join these terrific speeds and pressures, Scientist Svedberg enclosed his rotor so that it spins in hydrogen reduced to 1/30atmospheric pressure. Driving mechanism consists essentially of two turbines, the size of thread spools, against which oil is pumped at 800 lb. per sq. in. pressure. To prevent overheating of bearings, 45 minutes are required to work the rotor up to operating speed, 45 minutes more to slow it down. The rotor is oval in shape because an oval is less likely to fly apart than a circle.

The material to be centrifuged is placed in a tiny windowed cell in the rim of the disk. What goes on in the cell while the machine is spinning can be seen by stroboscopic light—extremely rapid, brief flashes from a mercury vapor arc. The flashes are timed to illuminate the cell at precisely the same point of every revolution and thus the cell appears motionless. A Zeiss camera nine feet long is trained on it to take pictures.

Last week’s visitors saw a few drops of hemoglobin, blood’s red coloring matter, being separated from the blood serum. In the Svedberg centrifuge this takes about six hours. By gravity sedimentation alone it would require 180 years. Du Pont expects the apparatus to shed light on the sizes and weights of the “giant” protein molecules in rubber, wool, silk, cellulose, hundreds of plastics.

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