Dear Matt: Does an empty tank of helium weigh more than a full one? Tanks. — Vik, La Mesa
Now that you’ve gotten that weighty question off your mind, is your head a little lighter? I’ll admit I’m kinda woozy after reading it. If I get your updraft, you’re guessing that one of those helium-balloon-fill-’em-up tanks weighs more once all the helium is used up than it did when it was full — that a certain volume of helium (light stuff) has been replaced by our grubby atmosphere (heavier stuff). Seductive logic, Vik.
To solve this one, the entire M.A. staff packed lunch boxes, stuck on those gummy name tags, got on a big yellow bus, and took a field trip. We’d barely had time to get to “85 bottles of beer on the wall” before we pulled into the lot at San Diego Welders Supply, 25th and Market, where, if you don’t already have gas, they’ll give it to you. Or sell it to you, anyway.
Once we’d piled out and lined up according to height, Bob, our tour guide, obligingly hauled out a petite-size helium tank and put it on the scale. The cast-iron cylinder was about 15 inches high, maybe 5 or 6 inches in diameter, and contained 22 cubic feet of helium under pressure of about 2000 psi. Full weight: 9.61 pounds. For the next three minutes or so, we talked in goofy cartoon-character voices as Bob drained the tank. Empty weight: 9.46 pounds. Bob took a bow, we all clapped. Then the whole SDWS staff lined up on the loading dock to wave goodbye as we linked hands and crossed the street to Golden Hill Liquor to buy a case of beer and some chips for the ride home.