(FORTUNE Magazine) – BEVERAGES HAVE COME in cans for more than 50 years, but in all that time the only major improvement in consumer convenience has been the pop-top, introduced in 1962. If the industry can digest a big change in the containers every 25 years or so, the time may be right for a second innovation: the self- chilling can. Two companies say they have developed beverage cans that refrigerate their contents quickly after opening, and both are talking about test-marketing their products this year. Eventually they hope to persuade beverage companies to replace conventional cans with the new ones, making the beer cooler obsolete and clearing acres of shelf space in the nation's refrigerators. By providing added convenience at nominal cost, the cans could become the latest marketing weapon for soda and beer companies. ''It's the next logical step in the soft-drink wars,'' says Jesse Meyers, publisher of Beverage Digest, a leading industry newsletter. The companies involved are Superior Marketing Research, a three-year-old concern based in Salt Lake City, and a New York City outfit called Laser Arms. Both are traded over the counter. Executives of Superior say their company recently acquired the rights to the technology from two inventors in Little Rock, Arkansas, and Hamilton, Alabama. Laser Arms claims it has rights to a process that another inventor has been working on since 1983. Douglas Brown, the 29-year-old president of Superior, says he doubts that Laser Arms has a workable can. Superior has demonstrated its product in public. Laser Arms has shown a version to would-be distributors but provided FORTUNE with only a diagram of it. The can works on the principle that when a compressed gas expands, its temperature falls. Inside each can is a metal capsule filled with carbon dioxide under high pressure. A valve releases the gas, cooling the outside of the capsule and thus the beverage. In volume production the process could add 2 to 5 cents to the 8-cent cost of making a conventional can. The carbon dioxide chills a beverage by about 30 degrees F. within a minute and a half. Both companies say they will market the process in standard 12-ounce cans. Because the capsule takes up two to 2.5 fluid ounces of space, consumers will pay more for less beverage. ALCOA TINKERED with a self-chilling beer can in the mid-1960s, but abandoned the project partly because it could not get the cost low enough to make the ! process economical. The principal technical obstacles that Laser Arms and Superior say they have overcome are in perfecting ways to inject the gas quickly and to vent it slowly so the gas does not simply chill the air outside the can. Brown says Superior is negotiating test-marketing agreements with PepsiCo and a Coca-Cola bottler as well as two of the top five U.S. brewing companies. He hopes that within two years the self-chilling can will be a fixture on store shelves. Making the cans may be easier than selling the idea to soda and beer companies, however. ''The beverage companies don't necessarily like us, because we represent change,'' says Brown. Some bottlers think the idea could fizzle. ''The concept might be worth something, but making it practical is another thing,'' says Jimmy Lee III, president of Buffalo Rock Co. of Birmingham, Alabama, the Pepsi bottling company that invented the three-liter plastic bottle. ''I'd say they've got their work cut out for them. It's not just like moving a product in a bigger package.''