The gas stored inside the cylinders that you find in your kitchen is LPG. LPG stands for liquefied petroleum gas. It is a naturally occurring by-product of extraction of natural gas and refining process of crude oil. There are lots of applications of LPG. It is used in commercial industries, transportation, agriculture, cooking (as fuel) and many more sectors. It is normally transported in cylinders or big tanks.
LPG is either propane or butane or a mixture of both the gases. The gas is stored in liquid form inside the cylinder. The name ‘liquefied gas’ indicates it is a gas at normal temperature and pressure. When subjected to modest pressure and cooling, it changes to liquid. The gas is liquefied and stored inside the cylinder. The reason for liquefying the cooking gas is that gases occupy more space than liquids or solids and are easy to compress. LPG evaporates at normal temperature and pressure. To allow for thermal expansion of the contained liquid, these bottles are not filled completely but between 80%-85% of their capacity. Inside the cylinder it is under high pressure so it has condensed into a liquid. When it is let it out from the cylinder into the air, it is under much less pressure and changes state into a gas.
LPG is heavier than air and can cause ignition or suffocation hazards when there is a leak. LPG is known to be energy-rich fuel with a high calorific value and one of the cleanest fuels contributing less carbon emissions than petrol or diesel. Adding less particulate matter to the air, it does not deteriorate the quality of air indoors. Basically these natural gases are odorless. Therefore a strong smelling agent like ethyl mercaptan (CH3CH2SH) is added to teh cooking gas so that small leak can be easily detected.