This is all about "Not So Standard Temperature and Pressure". The other day I learned that in USA, for most gases in refillable cylinders, "cubic feet" are at 70 °F and 1 atm. Am still seeking a proper reference giving the (different) STP values that apply when industrial and specialty gases are sold by the liter or cubic meter.
In high school I was taught that "STP" = 0 °C and 1 atmosphere. But back in 1982, IUPAC redefined the P in their STP http://goldbook.iupac.org/S05910.html to be exactly 100 kPa (1 bar; 1/1.01325 atm). That changed the value of "ideal gas molar volume at STP" from 22.4 to 22.7 liters. Did thousands of other references immediately become wrong?
This snip from Matheson catalog page for helium, http://www.mathesongas.com/industrialga ... strial.pdf, gives ft3 capacities numerically 38.0 to 38.1 times greater than m3 capacities. Same funny ratio appears in the tables for nitrogen, with all gas volumes slightly greater than for He (different story). Huh? Geometrically, a m^3 is only 35.3 ft^3. My unreviewed calculations say the 38:1 ratio is consistent with cubic feet measured at 70 °F and cubic meters measured at 0 °C. , but that doesn't make it official. Nor does seeing the same catalog pages give gas density & specific volume at 70 °F, 14.696 psia. Newbies must learn not to make unjustified inferences. That would be like reading different blocks in a neutron detector datasheet, and assuming that the sensitivity range in block A applies throughout the detectable energy range given in block B. (yes, I design calibration systems for expensive instruments for a living).
There's a similar discrepancy between ft^3 and m^3 units in bulk natural gas, because the "US" and metric NG trade units have different standard temperatures and pressures. Apparently the natural gas standard CF was defined, about a century ago, at 60 °F and 14.73 psia. I think the metric STP here is at 15 °C.
Unfortunately, Compressed Gas Association standards can't easily & honestly be viewed for free. After posting the original question, I found US NIST handbook 130-2012, "Regulation for the Method of Sale of Commodities" as adopted by The National Conference on Weights and Measures. http://www.nist.gov/pml/wmd/pubs/upload ... -final.pdf
Note that LPG, colloquially but inaccurately called propane, is not natural gas.2.16. Compressed or Liquefied Gases in Refillable Cylinders ...
2.16.2. Net Contents. – The net contents shall be expressed in terms of cubic meters or cubic feet, kilograms, or pounds and ounces. See Section 2.21. Liquefied Petroleum Gas for permitted expressions of net contents for liquefied petroleum gas. A standard cubic foot of gas is defined as a cubic foot at a temperature of 21 ºC (70 ºF) and a pressure of 101.35 kilopascals (14.696 psia), except for liquefied petroleum gas as stated in Section 2.21.
I am waiting for an answer from tech service at Sigma Aldrich about STP conditions for specialty gases by the liter.