NOVELTY - The apparatus has a liquid bath container (33) that contains a solution for washing off a metal impurity. A guide guides a movement of a porous metal substrate in the solution. The porous metal substrate is wound into a hoop (32) in a coil-shaped manner. The guide guides a movement of a sheet portion (32a) of the porous metal substrate unwound from the hoop. A winding mechanism (46) winds the sheet portion that is fed through the liquid bath container. A spraying unit sprays washing liquid for washing off the solution remaining on the sheet portion.    USE - Washing apparatus for washing off a metal impurity from a porous metal substrate such as foam nickel substrate and sintered alloy substrate, and for use as an electrode plate core for an alkaline battery such as nickel-cadmium battery and nickel-metal hydride battery, that is utilized for a power supply of a portable information terminal and a vehicle.    ADVANTAGE - The apparatus performs washing process to remove copper from the porous metal substrate in an effective manner, and has improved washing effects and efficiency. The washing apparatus measures the concentration in water i.e. drainage, sprayed against the sheet portion from the nozzles with the two-component concentration meter and measures acidity (pH) and ammonia concentration of the drainage, thus indirectly checking washing state based on the concentration measurement. The apparatus blasts away liquid droplets of the aqueous solution from the sheet portion with air shower produced by the blower, thus effectively removing residual components of the aqueous solution from the sheet portion. The apparatus dries the sheet portion by producing hot air blasted from the blower, thus drying the sheet portion efficiently and effectively. The washing apparatus separately detects the washing state at detection locations by utilizing the two-component concentration meter and the ammonia detector, thus checking washing state accurately. The metal impurities are efficiently washed off from the porous metal substrate. The highly reliable alkaline battery with a positive electrode plate including subtle metal impurities is efficiently manufactured.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) a method for washing off a metal impurity from a porous metal substrate for use as an electrode plate core for an alkaline battery    (2) a method for manufacturing an alkaline battery.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of an apparatus for washing an electrode plate core.    Hoop (32)    Sheet portion (32a)    Liquid bath container (33)    Winding mechanism (46)    Ammonia detector (47)