Air Inapparent

A mint-condition Queen Anne highboy or Paul Revere candlesticks may be coveted objects to the average antique hound. But two chemists with the Los Alamos National Laboratory in New Mexico are tracking down a more unusual relic: old air. Allen Ogard and Jane Poths are seeking samples of air that was sealed off decades or even centuries ago. Reason: to determine whether the level of carbon dioxide in the atmosphere has increased in the two centuries since the start of the industrial revolution. By some calculations, the extensive burning of oil and other fossil fuels has added to the shield of carbon dioxide around the earth, resulting in a heightened greenhouse effect that traps heat and changes weather patterns.

During the chemists' eight-month hunt, they scouted 19th century riverboats and pawed through the dusty corners of historical museums. The most promising sources are objects that were originally sealed against moisture, such as navigational compasses, hourglasses, sextants and telescopes. Other possibilities include buried time capsules, hollow building cornerstones, miniature globes and sealed containers salvaged from a ship that sank in the Missouri River in the mid-1800s. Two venerable Connecticut companies, which have manufactured hollow brass military buttons since the War of 1812, have offered to supply buttons spanning two centuries. "This gives us samples from many different periods of time," says Poths, "and all manufactured in one place." Some efforts, however, have been disappointing. The researchers had high hopes for a collection of ancient cremation vessels from a Buddhist mission in Hawaii, only to find that the lids were loose. Sighs Ogard: "Most things that can be opened have been."

To determine if a button or sextant is permeable, the investigators place the object in a container filled with neon, then later examine the item with a mass spectrometer to see if neon has entered it. If the object proves snug, its carbon dioxide is analyzed. Such an operation may require drilling a small hole through the antique object, but surprisingly, museum curators have not protested. Says Ogard: "Most have said it's fine as long as it's not in an obvious place ."