3221.     SMITHELLS, C. J.  Permeability of Metals to Hydrogen.  Nature, vol. 139, 1937, p. 1113; Chem. Abs., vol. 31, 1937, p. 6088.

        Rate of diffusion of H₂ was determined in cc. per cm.² per sec. at 760 mm. pressure for metal 1 mm. thick at 1,000°, 500°, and 0°.  Calculations were made for the following:  Fe, Ni, Mo, Pt, Cu, Al.  Apparatus for work at high pressures is made of steel to provide the necessary strength.  The diffusion of H₂ cannot be reduced greatly by increasing the thickness.  At room temperature, 1 mm. Cu would be as effective as 5 miles of steel, and 1 mm. Al would be better than 10¹³ miles of Pd in retarding this diffusion.