This business is next to nothing (Dec, 1950)
This business is next to nothing
By Louis N. Sarbach
IMAGINE a tunnel with one end beneath New York City’s Times Square. You enter a car at this end, stow your suitcase in the rack overhead and settle down comfortably with a magazine. You have been reading scarcely an hour when the vehicle stops. An escalator carries you back to the street level and you greet the light of day once moreâ€”in San Francisco!
Sounds like something out of pseudo-science fiction, doesn’t it? Yet it’s the idea of one of America’s most practical scientist-executives, General Electric’s noted physicist, Dr. Irving Langmuir.
“There is no fundamental reason,” says Doctor Langmuir, “why we could not travel at a speed of 2000 to 5000 miles an hour in a vacuum tube. Such a tube extending from New York to Chicago, or to San Francisco, could be constructed in which airtight vehicles would be magnetically suspended in space while moving forward at high speed. The Pacific coast might be only an hour away from the Atlantic.”
Doctor Langmuir’s cross-country vacuum tube is very much a project for the future, of course, but enough vacuum magic is going on right now to convince even the most skeptical that there’s more to “nothing” than meets the eye.
High vacuum â€” until recently a tool mostly confined to research laboratoriesâ€” plays a key role in a rapidly expanding list of industrial applications. Under high vacuum, vitamins and hormones are separated from their complex organic parent mixtures. Vital medicaments such as blood fractions and antibiotics, all notoriously unstable in the presence of heat, are safely freeze-dried in evacuated cabinets.
Lithium and magnesium, lively metals which eagerly unite with oxygen, are easily purified in furnaces from which all but a few stray molecules have been swept. Still other metalsâ€”gold, silver, aluminum â€”steam into luminous mists under vacuum, to condense a moment later as bright coatings on glass, paper, plastic and even fabrics.
To the housewife, high vacuum means flash-frozen foods. For the scientist, it plays a fundamental part in many new research tools: electron microscopes, mass spectrometers, synchrotrons, betatrons and cyclotrons.
For aviation people, high vacuum offers radar; for medical men, X-ray tubes; for the military, lenses of superior optical quality, and for all of us, the amazing magic of television.
Behind these developments is an army of new technologists, vacuum engineers, men who humorously call themselves “specialists in nothing.” These scientists spend their lives trying to produce the thing nature is said to abhor: a completely empty space. They haven’t wholly succeeded yet and perhaps they never will. But of the estimated 400 septillion (400 followed by 24 zeros) gas molecules that occupy every cubic inch of air at sea-level pressure, high vacuum experts have managed to pump out all but some 18 billionâ€” a mere trifle in this strange world of low pressure.
Why do we need vacuum in the first place? The most obvious reason is to prevent certain materials from reacting chemically with the gases of the air. In developing the incandescent lamp, Edison failed a thousand times until he realized that he would have to mount his electrical elements in an evacuated bulb to prevent the glowing filament from combining with oxygenâ€”from burning up, in other words. Vacuum’s newest and perhaps most interesting jobs have to do with materials too delicate to handle in certain ways under ordinary atmospheric conditions. At this point, let’s take a brief trip upward, where the air is thin.
Everyone knows that water evaporates. Its molecules are always in motion, always trying to escape from the surface. But air molecules, pushing downward, force most of the water molecules back into the liquid.
To help overcome this air pressure, we energize the water molecules with heat. They then can force their way through the air molecules and into the atmosphere. In plain language, water boils when it has been sufficiently heated.
Now, the fewer air molecules pressing down on a liquid’s surface, the less heat is needed to evaporate the liquid. That’s why water, which requires 212 degrees Fahrenheit to boil at sea level, boils at 187 degrees Fahrenheit on the 14,108-foot summit of Pikes Peak, where the air is a good deal thinner.
Going a step further, we can bring Pikes Peak down to sea level, so to speak, by chasing enough of the air molecules out of a sealed chamber. In such a chamber, water will boil at 187 degrees Fahrenheit at sea level.
What happens if we continue pumping out air molecules? The boiling point drops still lower. It even falls below the freezing point! When this occurs, ice turns directly to vapor, without passing through the water stage.
This “cold boiling” makes possible certain jobs once the despair of scientists. Penicillin, the miracle drug of World War II, quickly deteriorates in solution. For storage, it has to be bone-dry. The usual way to dehydrate anything is simply to build a fire under it and boil off the water. But penicillin breaks down in the presence of heat.
High-vacuum “freeze drying” solved the problem, not only for penicillin but for a host of other heat-sensitive organic substances: hormones, blood fractions (such as plasma), serums, protein solutions and the whole list of new antibiotic medicines.
Practically all foodstuffs contain heat-sensitive materials. That is why heat-dehydrated foods so often look unnatural and taste worse. With the new vacuum freeze-drying, foods not only keep their nutrient values intact but retain their original appearance and flavor.
In a typical process, a thin film of orange juice, running down the inside walls of a partly evacuated chamber, loses about 90percent of its water. The residue is frozen, canned and sold. Or it can be processed still further, sprayed on chilled vertical cylinders under high vacuum. The frozen coating gives up the rest of its liquid content, becoming a powder easily turned back into tasty orange juice simply by dissolving in water.
In the preparation of blood plasma, the liquid straw-colored plasma is separated from the red corpuscles in a centrifuge. It is then bottled, frozen and stacked on the shelves of a vacuum cabinet. As the inside pressure is pulled down, the water evaporates, forming as ice on condensers from which it is scraped by rotary blades. Eventually, shells of ivory-colored powder are all that remain in the bottles, which are then hermetically sealed. Penicillin, streptomycin and other heat-sensitive biologicals are dehydrated by the same process.
The new metal coating involves heat-sensitive substances, too. You can evaporate gold, silver and chromium without a vacuum â€” all you need is plenty of heat. But low temperatures are obviously needed to deposit films of these metals on such a material as paper.
This can be done only under high vacuum.
In the center of a vacuum chamber, a heating element melts and vaporizes the metal to be deposited. The roll of paper (or cloth or cellophane) is rapidly unwound (500 feet per minute) passing over the vapor rising from the molten metal, which condenses as an extremely thin film on the underside of the sheet. The coated paper rivals foil in brilliance.
Or, plastic articles are placed in racks and subjected to the low-temperature vapor cloud, from which they emerge evenly coated and no different, in appearance, from articles made of solid metal.
As vacuum coating becomes popular, you’ll see innumerable applications.
Already there are handsome metallized clock-cases, buttons, costume jewelry, sequins, decorative wrappings and ribbons. Zinc-coated paper is making its way in electronics for use in condensers. And aluminum-coated paper is being used in oil and wax-impregnated capacitors.
Lenses vacuum-coated with magnesium fluoride are rapidly replacing the old uncoated type in periscopes, telescopes, binoculars, cameras and other optical instruments. The microscopically thin film of the transparent salt cuts surface reflection to a remarkable degree.
On the other hand, if bright metals (silver or aluminum), instead of magnesium salt, are condensed on optical flats, the result is a mirror. These vacuum-coated mirrors, superior to those made in the conventional way, are used in precision devices: machine-tool comparators and infrared spectrographs, in television and astronomical instruments and in the latest types of sealed-beam headlights.
Quartz radio crystals are “loaded” with gold film under high vacuum until they vibrate at precisely the desired frequency. Then silver film, also vacuum-deposited, provides bases for soldering electrical leads to the crystals.
A particularly fascinating application of high-vacuum coating is metal shadow-casting, used by scientists in connection with the new electron microscope. The metallic mist is directed against the specimen to be studied, at an oblique angle. Irregularities on the surface of the specimen cause thickness variations in the layer of metal. This produces shadows from which heights and depths of the surface irregularities can be calculated.
Molecular (or “short path”) distillation is still another of high-vacuum’s important new jobs. Vitamin concentrates from fish oils, fine lubricating oils for watches and purification of hormones on a commercial scale are but three from a growing list of applications.
Vacuum engineers have upset the old theory that certain oils are “fixed”â€”undis-tillable. Under high vacuum, their long, delicate chains of molecules are tenderly handled, protected from disastrous bumps by the molecules of the air.
It was Dr. K. C. D. Hickman who first thought of molecular distillation, thereby providing millions of Americans with vitamins in convenient capsule form instead of thick, yellowish, evil-tasting cod-liver oil. Doctor Hickman mounted a heated, whirling disk inside an evacuated glass bell jar.
Fish oil, fed to the center of this “spinning pie plate,” spreads outward in a thin film. Almost instantaneously the lightweight vitamin-bearing esters vaporize and condense on the bell jar’s cool surface, from which they are collected and shipped to food and pharmaceutical concerns.
Three types of pumps are used in high-vacuum work:
Jet pumps trap air or gas molecules and sweep them forward in a high-speed jet of steam or oil vapor. The air goes into the atmosphere; the vapor condenses and returns to the boiler for recirculating.
A single pump of this type can lower pressure to about 50 millimeters (around one fifteenth of atmospheric pressure at sea level). Hooked up in series, five pumps can cut this to as little as .03 millimeter. Such pumps are favored where large volumes of air or gas have to be handled at high speed and where higher vacua are not required.
In the most efficient oil-sealed mechanical type, a rotor revolves eccentrically within a cylindrical chamber so that air (from the container being evacuated) is admitted to the chamber. As the rotor revolves, the container is automatically sealed offâ€”at the same time, the air in the pump chamber is compressed into a small space and driven off through a vent, into the outside atmosphere.
These mechanical pumps work fast, the rotor turning at the rate of 600 revolutions per minute. But the highest vacuum possible with such equipment (about .001 millimeter) is still a far cry from the kind of emptiness needed in many of the new applications.
The real evacuator is the diffusion pump, which uses a curtain of mercury or oil vapor as a jet for dragging out the air or gas molecules. In one form of diffusion pump, mercury or oil of low boiling point is heated in a tank at the bottom of an inverted U-shaped tube. High-pressure vapor soon rises in one arm of the tube and rushes past the opening of the space to be emptied, sweeping off air molecules by the billion.
The process is speeded by stages of ejector orifices along the way, which keep building up the pressure of the vapor. In its passage down the other arm of the tube, the vapor condenses on the cool sides and returns to the tank, to be vaporized once more. The air molecules, meanwhile, are drawn off by a mechanical pump.
Developed by Doctor Langmuir back in 1916, the diffusion pump is capable, in theory at least, of producing a perfect vacuum. The latest types, used in advanced laboratory research, leave such a small amount of gas that it would have to be increased at least ten trillion times to bring it back to normal atmospheric pressure.
That’s about as close to nothing as any human being has come, thus far.
Running an industrial process in such an evacuated space would be like taking a factory off the surface of the earth and moving it up into the ionosphere.
Ten years ago, high vacuum was confined almost entirely to the laboratory. Today, its industrial uses have expanded until it has become one of industry’s most valuable and promising tools.