I read, as a child, the waft mode of telling what a chemical smells like. The kids laughed at me, in my junior high chemistry days, so I stopped, and just started sniffing. That is a bad idea, in my college basic chemistry days, I was kinda hit or miss -- if I knew a gas was coming, I wafted, but once I was doing some sort of reaction with a nitrogen compound, and I got a brown gas, and I sniffed instead of wafted and ... ow, NO2, smells like ... burning.