Monday, September 28, 2015
“Why do I have a garbage can full of liquid nitrogen? Because I’m a chemist,” Doug Mulford, director of undergraduate education for Emory’s Department of Chemistry, told a crowd of enthralled children and adults.
Decked out in safety glasses and a red lab coat printed with flames, Mulford conducted a ribbon immolation ceremony on Saturday, to officially open Emory’s Sanford S. Atwood Chemistry Center addition. The crowd gasped and cheered in the courtyard as Mulford ignited a thermite reaction, a pyrotechnic mixture of aluminum and iron oxide. The reaction shot off sparks and smoking-hot globules of molten iron to sever the ceremonial ribbon.
Rain did not dampen anyone’s enthusiasm for the grand opening, which included fun science demonstrations by students from chemistry, biology and physics.
In fact, chemists love water droplets and clouds. Graduate students from Emory’s Pi Alpha Chemical Society showed how to make both, using liquid nitrogen.
“We’re pouring really hot water into really cold liquid nitrogen, causing it to expand into a plume of air that comes up as a cloud,” explained Daniel Collins-Wildman, who braved nature’s drizzle in the courtyard along with fellow graduate student Amanda Dermer.
In fact, Collins-Wildman said, the liquid nitrogen is so cold (77 Kelvin) that ice particles form in the cloud, creating what is known as a nucleation site where water drops can form.
“I conducted an experiment with this by accident once, when I was making macaroni and cheese,” he said. He brought the water to a roiling boil. As usual, bubbles formed along the sides of the pot, where the temperature is higher and the pot’s irregular surface creates the potential for nucleation. Then the power went out. The bubbles on the sides of the pot disappeared. The water was still hot when he turned the heat back on. Without the small bubbles acting as nucleation sites the water boiled violently, a phenomenon known in chemistry as "bumping."
"I heard this weird sound," Collins-Wildman said. "All those little bubbles that had formed slowly before, this time formed immediately as one huge bubble that came to the surface with a BLURP!”
Chemistry Center turns up the heat for grand opening