'This gas, atomic No. 2, is used as a tracer in detecting leaks in gas lines'
helium
IT'S A GAS: This gas, atomic No. 2, is used as a tracer in detecting leaks in gas lines
This gas, atomic No. 2, is used as a tracer in detecting leaks in gas lines
This gas, atomic No. 2, is used as a tracer in detecting leaks in gas lines
IT'S A GAS
helium
IT'S A GAS