How It’s Used Hydrogen (aka “waterstuff,” dihydrogen) is a colorless, odorless, flammable gas. Once ignited, it burns with a pale blue, almost invisible flame. Although hydrogen is the most abundant element in the Galaxy (ten times as abundant as helium, the next most widely occurring element), it makes up only about 0.14 percent of the … Continue reading Hydrogen—and Hydrogen Monitoring Instrumentation