This is Calgaz aluminium cylinder, filled with CH4 & N2. This brand of calibration gas is well known for its reputation, recommended by those instrument company such as Honeywell. We could supply these in any mixture as per requested by customer.  

Calibration gas, also known as specialty gas or calibration gas mixture, is a precisely mixed and certified blend of gases used as a reference standard to ensure the accurate functioning of analytical instruments, particularly gas detectors and analyzers.

Calibration gases can be single-component (e.g., pure carbon monoxide) or multi-component mixtures (e.g., a mix of methane, carbon monoxide, and hydrogen sulfide). Common gases used in calibration mixtures include:

Carbon Monoxide (CO)
Carbon Dioxide (CO2)
Hydrogen Sulfide (H2S)
Methane (CH4)
Oxygen (O2)
Nitrogen Dioxide (NO2)
Sulfur Dioxide (SO2)
Ammonia (NH3)
Hydrogen (H2)
Various hydrocarbons (e.g., propane, butane, pentane)
The specific mixture depends on the type of instrument being calibrated and the gases it's designed to detect.