Every railroad corporation whose cars are propelled by steam shall cause a power brake to be attached to every passenger car used for conveyance of passengers, which brake shall be so arranged that it may be put in operation by the engineer when the train is in motion. Every railroad corporation that shall use any passenger car for the conveyance of passengers, without the power brake so applied, shall for every offense be fined one hundred dollars ($100), one-half (½) thereof to the use of the complainant and one-half (½) thereof to the use of the state; but this penalty shall not apply to an incidental conveyance of passengers in freight cars, nor to “dummy cars,” so-called, nor to a passenger car attached to the rear end of a freight train or dummy engine.