For whitening letters engraved on electro-plate, dissolve 5 dr. of silver nitrate in 1/2 pt. of distilled water, and add enough potassinm cyanide solution to throw down the silver in white curds, and then to dissolve these curds. Procure a strip or a stout wire of pure silver, wrap a few folds of cotton rag round one end to form a small mop, and connect the other end to the silver or copper plate of a Smee or Walker battery of one or two cells. Connect the engraved plate to the zinc plate of the battery, soak the mop in the silver cyanide solution, and pass it along each line until all the lines are nicely silvered.