Baking soda and Hydrocloric acid?

My professor use filter flask with rubber hose attached. He mixed baking soda and hydrocloric acid together. Then he put the end of the hose to cylinder. When the reaction ends, he put a light candle into the cylinder, and the lighted candle went off. When he puts water and swirl it into the cylinder, he put another lighted candle into the cylinder. The light became brighter and didn't went out. I'm so confused why the candle didn't went out. Someone helps?