GASCO Precision Calibration Gas 34es-455X Mixture 25 PPM Hydrogen Sulfide, 0.35% Pentane (25% LEL), 19% Oxygen, Balance Nitrogen Contained in a 34 Liter Factory Refillable ecosmart Disposable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA