§ 51. Weight of rail. The rail used in the construction or the
relaying of the track of every railroad hereafter built or relaid in
whole or in part shall be of iron or steel, weighing not less than
twenty-five pounds to the lineal yard on narrow-gauge roads, and on all
other roads not less than fifty-six pounds to the lineal yard on grades
of one hundred and ten feet to the mile or under, and not less than
seventy pounds to the lineal yard on grades of over one hundred and ten
feet to the mile, except for turnouts, sidings and switches.