BACKYARD INVENTORS; Following in Edison's footsteps

Despite the problems - discouragement, a dozen near-bankruptcies, the explosion that blew off his roof - Jacob Greenberg says he still treats salt shakers with respect.

Dr. Greenberg is an inventor. He works in a small cinder-block building near the edge of the pine barrens, in an area of south New Jersey William Penn once declined as uninhabitable. The lab may have been yellow when new; age and auto emissions have faded it to a slightly belligerent shade of beige. Inside, in various states of assembly, are large machines that look like a cross between steam boilers and a mutant Hoover upright. They are hazardous waste incinerators , able to eat many of the deadly chemicals now leaching into the south Jersey soil from dumpsites like the infamous Price's Pit, just a few miles away.

Their secret ingredient is, well, salt. Not quite Morton's, but a close relative.

''People say 'salt? Is that guy crazy? Look what it did to the rocker panels on my car,''' sighs Greenberg. Thirteen years of frustration have at least provided him with some good lines.

Independent inventors are not extinct. Endangered, perhaps; angry and bewildered, certainly.

They are butchers and scientists, retirees and engineers. Their ideas can be sophisticated, like Greenberg's. They can be frivolous (''My cologne was always wearing off,'' says one inventor. ''So I thought, why not a ring that dispenses perfume?'') A few are downright unworkable. (An engineer leans across the drill press in his workshop. ''Confidentially,'' he whispers, ''I'm working on an electric motor that produces 27 times the power it consumes.'')

But the tinkering goes on, in backyards and basements, in drab buildings out by the highway, where rent is cheap. And all the tinkerers would probably echo Greenberg's words:

''You know,'' he says, ''either I'm a first-class lunatic, or I have a lot to contribute to society.''

All inventors do not have tousled hair, a German accent, and assistants named Igor. Most of them work during broad daylight, and none, apparently, live in a castle. Granted, their workshops are messy and many are demonstrably poor drivers, but the traditional images of modern inventors - mad scientists and cranks - are nowhere close to the truth.

Inventors come from ''a complete cross section of the population,'' says George Lewett, head of the Office of Energy-Related Inventions at the National Bureau of Standards.

''The only generalization you can make is they're all different,'' says a government engineer. (One exception: few women invent. Historically, they have been issued only about 2 percent of US patents.)

The independents have produced much more than self-tipping hats and furnaces that burn Alaska crab shells. One well-known inventor, Jacob Rabinow, says most of this century's major inventions, except color TV and the transistor, came from individuals. Studies done for the Department of Commerce put the figure closer to 50 percent.

Independent inventing formed the basis of computers, lasers, and photocopying. Light polarization, used in many sunglasses, was discovered in a rented room by young Edwin Land. According to a National Science Foundation report, many aluminum fabrication techniques were first developed by independents, as were seven of thirteen major advances in steel production during the decade following World War II. Eugene Houdry, inventor of a practical way to catalytically ''crack'' crude petroleum in the refining process, was unemployed (though the son of a wealthy family).

But if you go by the numbers, these are tough times for today's Edisons. In 1954, 44 percent of patents issued went to individuals. In 1974, it was 25 percent. By last year, the figure had dropped to around 23 percent.

And experts say only one percent of those patents ever earn money for the inventor.

''Things are increasingly difficult for independent inventors,'' says Richard Stockel, director of the New Jersey office for Promotion of Technological Innovations. ''They're definitely struggling.''

Inventing is expensive. Ideas are free, but prototypes can cost upwards of $ 10,000, even for a consumer product. And it's almost impossible to sell something that exists only on paper.

Technology is getting more complicated all the time. Deprived of the technical libraries and scientific camraderie of corporate labs, it can be hard for the independent to keep up.

''In some areas, the technology is so advanced that if you don't keep up you can't contribute,'' says George Lewett.

And after an inventor has struggled and sweated to bring an idea to market, often mortgaging everything he owns on the promise of the future, he sometimes finds his patent has the protective qualities of Kleenex tissues in the rain. For example, the Eighth and Ninth Circuit Courts of Appeals have struck down 83 percent of the litigated patents brought before them in the past two decades.

Why invent anything, with such difficulties poised to swoop at a moment's notice?

''I think it will be very successful, make me millions of dollars, and make me very happy,'' says Eric Howlett, a Boston inventor perfecting a 3-D camera.

Perhaps inventing is a natural, irresistable process, like breathing or eating glazed doughnuts.

''It's always bothered me that there are so many problems, and the solutions are right there among us,'' says Martin Noone, another Boston-area tinkerer. ''I've never met a person in my life who isn't an inventor.''

Americans have always considered themselves an inventive country. ''Yankee ingenuity'' may be one of our most fundamental myths, part truth, part nostalgia , part Madison Avenue. In the picture of our past, how important were backyard inventors?

Consider the lightbulb. ''In fact, Edison was a slob,'' says Peter Cousins, a curator at the Henry Ford Museum.

Cousins peers down the bottle-lined walls of Edison's Menlo Park laboratory, now at Greenfield Village, an outdoor museum founded on Henry Ford's vision of the hero-inventor. ''When Edison saw this after it was rebuilt, he said 'our floor was never this clean.'''

Along with Whitney, Watt, and Ford himself, Edison has long symbolized the golden age of hero-inventors. But instead of the lightbulb, his most brilliant invention may have been the modern research and development lab, which he pioneered at his Menlo Park complex.

Edison's assistants were specialists, such as glassblowers and mathematicians , whose skills fitted together into a unit able to design the many products needed for a complete lighting system - switches, meters, fuses; a plethora of gadgetry. With their help, Edison produced 421 inventions at Menlo Park. Costs reflected the size of the operation: Edison estimated that he spent $40,000 on light bulb experiments before the famous bamboo filament stayed lit.

''He had that spark of genius,'' says Edward Pershey, curator at the Edison National Historic Site. ''But part of that spark was to see he needed trained people working around him.''

Historians say the spark of invention often does come from a single person, but that the process of innovation - developing the invention into a final product - is just as important, and involves many people.

''We cling to John Wayne and the idea of the individual inventor,'' says Dr. John Lankford, history professor at the University of Missouri. ''You know, you go out to the barn with a battery and some wire and heaven knows what you'll have by sundown.''

The heart of American technological growth may, instead, be the rise of systems - mass marketing and mass production, or, as one historian puts it, ''realizing how crummy you can make something and still have it work.''

But, relative importance aside, the spark is still invention. Innovation experts claim America is a uniquely creative country, where many people refuse to know their place and keep tinkering, against all odds, sometimes wondering themselves, while waiting for the glue to dry, why on earth they go on.

Back in New Jersey, Jacob Greenberg is making salt sound like the greatest thing since hand-held calculators. By putting pipes through a block of salt, he claims, you can apply a direct flame - and construct a furnace four times more efficient than a traditional design. In one conversation he can quote Gore Vidal , Thomas Carlyle, the newest Solzhenitsyn, and explain why some shampoo contains arsenic (''it's an anti-fungicide.'')

Fifteen years ago, Greenberg was a top NASA scientist in Ohio, specializing in fuel cells. Disturbed by the dirty palm-print of industrial pollution, angry that after a dip in Lake Erie he had to ''shower for three days,'' he quit to work full-time on building new machines for scrubbing the environment.

''My peers said, 'Are you stupid enough to think a major technology can come out of a backyard in today's society?''' he says.

Through his work at NASA, Greenberg had become convinced that a bed of molten salt would swallow many pollutants more efficiently than existing hazardous waste incinerators, which tended to be gangly machines with more after-burners than a moon rocket.

From this idea, he developed the machines that now stand silent in his damp lab. They work when waste is fed into a pan floating on molten salt. The waste burns, forming gases, while unburned, leftover particles are periodically removed from the pan. The gases then meander into a second chamber, where they are sucked down into the hot liquid. Then, in Greenberg's words, the molten salt ''does chemistry.'' It acts as a catalyst, speeding up chemical reactions that would otherwise require enormous temperatures and pressures. In this way the remaining pollutants are burned, or coaxed to rearrange themselves into harmless compounds by a chemical ''getter'' dissolved in the salt. When the process is over, all that remains is a little ash, carbon dioxide, and steam.

By mixing different types of salts, from table salt to more exotic varieties, with different ''getters'' (lime, for instance, ''gets'' sulfur dioxide) Greenberg can adjust his salt bath to cleanse a whole gamut of wastes - from sewage to tanning effluents to left-over chemicals.

Today Greenberg seems closer than ever to financial success. A New York firm, Questex, Inc., has brought in fresh capital and management skills to help him gear up for another marketing push. But, for his business, the road to this point was full of potholes.

For years, says Greenberg, he never had enough cash, and bounced from investor to investor. He went on the market before his machines were ready. He found that chemical companies, rather than buy his machines, preferred to wash their hands and pay someone else to dispose of waste.

One day, the senior management of a company interested in licensing came to Pleasantville for a demonstration. Greenberg blew off his roof. (Under certain conditions, salt can be explosive.)

''The idea alone is not all that counts. As creative as you are on the technical side, you need to be that creative on the business side,'' he says.

Greenberg lingers by his machines, waving his arm inside to show where the salt is, patting their metal skin and outlining ducts, baffles, and flames: the salt goes here, the gas goes there, the flame goes on and whoosh! harmless exhaust floats toward the high-rise casinos of Atlantic City.

''Will you ever pick up a salt shaker again in quite the same way?'' he says, laughing. ''Every innovator is like every other human being. A builder.''

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