A dump bailer for downhole placement of flowable materials in a wellbore. The dump bailer has an elongated housing with a cavity for placement of the flowable materials. The housing has an open bottom. An expendable cap or plug, of a magnetic material, is held within the open bottom by a shear pin, sufficient to hold the plug in place with the material within the cavity. An electric solenoid surrounds the plug. Energizing the solenoid coil by electric current creates a magnetic field which overcomes the shear pin and forces the plug out of the open bottom. The material may then flow out of the cavity. Alternatively, a sliding sleeve may be disposed in the open bottom, which moves from a first closed position to a second open position, in response to the magnetic field.