Ask Denise Kelleher when Thanksgiving Day was in 1914. Tell Jane Larsen you need to know if it's safe to varnish wood salad bowls. Ask Elizabeth Warren how often millipedes lay eggs. Demand to know the spelling of "Merthiolate."

Those are the easy questions.

The queries funnel into the main building of the Arlington County library system, over the phone and across the desk, into the ears of Kelleher and Larsen and Warren and the other reference librarians. Between 300 and 600 questions a day. About 3,500 a week.

Give the librarians a minute, and they'll tell you the divorce rate in D.C. in 1980 (7.3 per 1,000). Give them a little longer, and they'll track down the tale of the Greek god Dionysus, taken prisoner by a pirate band. Give them your phone number, and they'll look up the answer and call you back. No questions asked.

"There is no pleasure greater than tracking down a tedious little fact and getting it," says Larsen.

For the librarians, this is a grand game, an intellectual scavenger hunt played to the tune of "Beat the Clock." No matter how much knowledge they hand over the counter, the inquisition never ends:

What was the number on Joe DiMaggio's jersey? (5). What are the ingredients of lighter fluid? (Deodorized naphtha and oil of citronella.) Was there ever a glacier where Arlington is now? (No.)

At the central library reference desk, lighted telephone buttons wink constantly, unanswered questions humming at the other end. Quizzical looks line up in front of the desk.

The questioners are hurried or apologetic, distracted or earnest. But they all need to know. Preferably now.

A tenth grade term paper may rest on the outcome of the inquiry. A little wager may teeter on a certain historical fact. The librarians know this is no trivial pursuit.

"The fun thing about this job," says librarian Nancy Cooper, "is you never know what's going to be asked next."

Sometimes the answer is close at hand: They want the Northern Virginia Yellow Pages, or a pencil, or page 91 of the federal tax form booklet.

The librarians like the hard questions.

"The ones that excite me are the ones that are hard, or where I find the answer when I didn't think I'd be able to, or that are historically interesting, like, 'What's the origin of chocolate?' " says Kelleher.

One recent afternoon, a middle-aged man approaches the reference desk with a newspaper article containing the word "zaftig" and a puzzled look on his face. Warren points him toward the Yiddish dictionary.

A caller wants to know who said, "A ship can't have two captains." Larsen checks five books of quotations and finds nothing.

"Sometimes people will call and want the source of a quote, and maybe their Uncle Henry said it 30 years ago," she explains. "Or maybe they read it on a greeting card." But she keeps looking: "Five sources is our minimum."

Sometimes the questioners know exactly what they want: "I'm looking for articles on pigs in New Guinea, but not about diseases or animal husbandry."

Other times, the questions are a little vague, and the librarians have to play detective.

"Sometimes they come in and they can't remember the author or the title, but they know they read this book, and maybe they remember what color it is," says Warren.

The questions are wise and whimsical, academic and amusing. Some of the answers stick with the reference crew long after the questioner is satisfied. Eileen McMurrer will always know what a charmed quark is. Kelleher will never forget that a group of frogs can be called a colony, a froggery or an army.

A box on the reference desk, dubbed "Pandora," holds the answers to recurring inquiries, such as the names of Santa's reindeer.

The phone rings again, the folks line up, the questions pour forth.

Gwyn Williams, a tenth grader at Yorktown High School, is writing a paper on racial discrimination. Kelleher shows her the magazine index and the section on black history.

A man with an idea for a novel needs the 1986 Writer's Market. Someone wants population figures for Arlington in the past decade. A caller requests the correct spelling of "baklava." A woman wants pamphlets -- not magazine or newspaper articles, but pamphlets -- on the homeless.

Are the librarians ever stumped? Kelleher hesitates, then explains what might be a reference librarian's maxim: Old questions never die, they just get referred elsewhere.

She recalls sending a caller to Georgetown University to find out the frequency of letters occurring in French words. She can't think of too many others that went unanswered.

Two-and-a-half hours and 10 quotation books later, Larsen still can't find a source for "A ship can't have two captains." She calls back and reads several similar quotations from the Dictionary of Military and Naval Quotations, and identifies their authors.

Ten minutes later, Larsen is searching again -- this time for the size of the Egyptian pyramid Khufu. She is on her knees in front of the Encyclopaedia Britannica. She utters a small confession: "We don't have to be experts in anything. We just have to know where to look."