using an ultra sonic sensor for gas detection:
Sound velocities
gasses (0C), m/s,ft/s
dry-air,331,1066
ammonia,415,1362
argon,308,1010
CO2,259,850
CO,338,1109
Chlorine,206,676
deuterium,890,2920
ethane (10 C),308,1010
ethylene,317,1040
helium,965,3166
hydrogen,1284,4213
hydrogen bromide,200,656
hydrogen chloride,206,676
hydrogen iodide,157,515
hydrogen sulfide,289,948
illuminating coal gas,453,1486
methane,430,1411
neon,435,1427
nitric oxide (10 C),324,1063
nitrogen,334,1096
nitric oxide,263,863
Oxygen,316,1037
Sulfur dioxide,213,699

Vapors (97 C)
acetone,230,755
benzene,202,663
carbon tetra-chloride,145,476
chloroform,171,561
ethanol,269,883
ethyl ether,206,676
methanol,335,1099
water vapor (134 C),494,1621