For rough estimation: Take 1.5 cubic feet as physical volume of "H" cylinder and assume perfect gas laws.
One Navy cylinder was marked 1800#, the other 2260#.
Therefore, Amount of helium at N.T.P. when pressure reads
p (p.s.i. at 70 degrees Fahrenheit) = (1.50)((p+14.7)/(14.7))(273/294)=(1.394)((p/14.7)+1)
"H" cylinder:
at 1800 p.s.i. : 173 cubic feet (0 degrees Celsius, 76 cm Hg)
at 2260 p.s.i. : 216 cubic feet (0 degrees Celsius, 76 cm Hg)
at 1800 p.s.i. : 1.92 lbs. of He gas.
at 2260 p.s.i. : 2.40 lbs.
If He in balloon and air outside at same temperature, the lift per pound mass of helium is (29-4)/4 = 25/4 = 6.25 lbs.

For rough estimation: Take 1.5 cubic feet as physical volume of "H" cylinder and assume perfect gas laws.
One Navy cylinder was marked 1800#, the other 2260#.
Therefore, Amount of helium at N.T.P. when pressure reads
p (p.s.i. at 70 degrees Fahrenheit) = (1.50)((p+14.7)/(14.7))(273/294)=(1.394)((p/14.7)+1)
"H" cylinder:
at 1800 p.s.i. : 173 cubic feet (0 degrees Celsius, 76 cm Hg)
at 2260 p.s.i. : 216 cubic feet (0 degrees Celsius, 76 cm Hg)
at 1800 p.s.i. : 1.92 lbs. of He gas.
at 2260 p.s.i. : 2.40 lbs.
If He in balloon and air outside at same temperature, the lift per pound mass of helium is (29-4)/4 = 25/4 = 6.25 lbs.