What is its composition?
Other compositions include "town gas" or "coal gas", a mixture of H_2 and CO which used to be used to fire gas cookers. So-called "beer gas", a mixture of food-grade carbon-dioxide, and dinitrogen, is used in the hotel industry to dispense drinks.
There is also "heliox", a dioxygen/helium gas mix that is used for deep-sea diving. I read here that this mix is currently being used (with some success!) for chronic asthma attack. Anaesthetists also probably have access to a range of specialty gas mixtures for their patients.
