Related Clues:

• Scientific discovery of 1894
• Element 54
• Vacuum tube filler
• It's a gas
• Number 18
• It doesn't react well
• About 1% of the atmosphere
• Light bulb gas
• Hard-to-combine gas
• Element in arc lamps
• Odorless gas
• One of the noble gases
• Arc lamp gas
• Noble gas
• Incandescent lamp gas