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RESEARCH
Carbon Black Controls Clouds Carbon black cloud seeding makes weather to order A NAVY chemist has proved that carbon black can make or break a cloud. She is Florence \V. van Straten, now working with the Navy W e a t h e r Serv ice. W h a t van Straten's discovery means in terms of scientific w e a t h e r control is now being measured by Naval Re search Laboratory. But she has al ready demonstrated that carbon black, absorbing heat from the sun, can change atmospheric conditions enough to create clouds or to break them up quickly. F o r some time, van Straten believed she could modify clouds by influencing temperatures in parts of the atmos p h e r e . I n this manner, she says, cloud masses t h a t exist could b e dissipated, a n d , u n d e r sonie conditions, cloud masses could be created. She reasoned further t h a t carbon black would be the ideal material to induce the tempera t u r e variations because of its ability to absorb h e a t . • Testing Among t h e Clouds. In tests conducted from a Navy Constella tion over the Georgia coast, a pound a n d a half of carbon black sprinkled on top of a cloud dispelled the formation in 2 0 minutes. This w a s a large cloud. F r o m its base, hovering around 5000 feet, it extended into t h e air as high as 11,000 feet. Smaller clouds disap p e a r e d in three to four minutes after finely divided carbon was dropped, she asserts. Van Straten's theory on the cloud b r e a k u p amounts to stabilizing unstable air. Introducing the carbon black into t h e top of the cloud reduces its cooling rate. This tends to stabilize the atmos phere, a n d the cloud shrinks to a wisp in minutes. Creating clouds with carbon black seeding hinges on t h e amount of mois ture in the air, van Straten says. It would hardly work in the air over the
Chasing Clouds. In a n experiment done by a Naval Research Laboratory-Navy l e a t h e r Station team, clouds (above) get seeded with particles of carbon "black. Below, cloud is shrunk to a small size I S minutes after seeding*. Carbon black absorbs heat from the sun. This changes atmospheric conditions enough to create clouds or to break them u p in a matter of minutes
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RESEARCH j Sahara, she adds. But in the Georgia the w a n n e r ones in a distillation procj tests, carbon black strewn through a ess, would grow heavy and fall a s rain. | la\ e r of moist atmosphere did produce N R L is now conducting tests on cloud I clouds. The black was seeded on a modifications with carbon black t o ! mile run at about 4000 feet. By the measure distribution of t h e carbon o n ! time the plane turned a n d started back, release, rate of growth of w a t e r d r o p clouds had started to form between lets, and temperature effects before 3000 a n d 60ÛO feet. Here, van Straten and after seeding. sa\-s, as t h e carbon black absorbed heat, With these data, van Straten says it produced temperature differences be- tests on fog and thunderstorms will b e tween tlie seeded atmosphere and the carried out with much more knowunseeded. T h u s , instability grew how than that existing when the cloud rapidly, and t h e clouds formed. tests were made. If these are successW h a t was not recorded in the Geor- ful, equipment and techniques will b e gia tests was whether any rain fell as a worked out for using die method t o result of the seeding. However, if van control weather from aircraft, bases, Straten's hypothesis holds, a cloud and ships. She says it is too soon t o created by carbon seeding could be- speculate on t h e value of her carbuu come a thunderhead. Rain would be black technique to the military or t o produced when wanner droplets—those industry. Presumably, though, it could heated b y the carbon black—moved up- be used to start and stop rainfall, break ward into the neighborhood of cooler u p fog and thunderstorms, and to condroplets. The cooler drops, picking u p trol hurricanes and tornadoes.
Europe Looks at U - 2 3 5 new uses for \JVJ
U LI U
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At the Geneva Conference, European countries talk about their studies of isotope separation
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Ο XLY the United States, Great Bri tain, a n d the Soviet Union have uranium-235 processing plants. Now France is thinking of building one, and other continental countries are investi gating processes, too. Gaseous diffusion is the method of isotope separation used in all large U-**'*"· plants. Uranium, as gaseous uranium hexafluoride. is allowed to diffuse through a barrier having very fine pores. Since the U 2 3 î i atoms are slightly lighter than the U j : t e they diffuse through the barrier pores faster. So material passing through the barrier is slightly enriched. Repeating this operation many times in a cascade system gives t h e desired degree of enrichment in U 2 3 S . • French W o r k . T h e big problems in a uranium-235 plant are developing and fabricating satisfactory porous barriers, preparing and purifying uranium hexafluoride, corrosion from UF t î . measuring isotope concentrations, and solving various chemical engineering problems o n relationships between the stages, C . FreJacques and Olegh Bilous told the Second United Nations International Conference on the Peaceful
Uses of Atomic Energy in GenevaBarrier material!» have- tt> l)c uioSt carefully chosen. The separating units containing them constitute almost a quarter of the cost of a plant. An effective porous barrier should have pores with radii between 100 and 3 0 0 A. For good permeability it should b e as thin as mechanical strength allows.
These porous barrier tubes a r e m o u n t e d in the French gaseous diffusion plants to separate the uranium isotopes
