If you cannot afford to floor the whole of the battery with smooth concrete, at all events smoothly concrete the floor of the cleaning-up room, and let the floor slope towards the centre: where a sink is provided. Any lost mercury must thus find its way to the centre, where it will collect and can be panned off from time to time. Of course an underground drain and mercury trap must be provided. IRON EXTRACTOR. When using self-feeders, fragments of steel tools are especially liable to get into the battery boxes or other crushing appliance where they sometimes cause great mischief. I believe the following plan would be a practicable remedy for this evil. By a belt from the cam or counter shaft, cause a powerful electric magnet to extract all magnetic particles; then, by a simple ratchet movement, at intervals withdraw the magnet and drop the adhering fragments into a receptacle by automatically switching off the electric current. A powerful ordinary horse-shoe magnet might probably do just as well, but would require to be re-magnetised from time to time. TO SILVER COPPER PLATES. To silver copper plates, that is, to amalgamate them on the face with mercury, is really a most simple operation, though many battery men make a great mystery of it. Indeed, when I first went into a quartz mill the process deemed necessary was not only a very tedious one, but very dirty also. To amalgamate with silver, in fact, to silver-plate your copper without resort to the electro-plating bath, take any old silver (failing that, silver coin will do, but is more expensive), and dissolve it in somewhat dilute nitric acid, using only just sufficient acid as will effect the purpose. When the crystals have formed, add sufficient clean quick mercury to form a thick pasty amalgam; moderate heat will assist the process. After some hours place the ball of amalgam in a piece of strong new calico and squeeze out any surplus mercury. About an ounce of silver to the foot of copper is sufficient. To apply it on new plates use somewhat dilute nitric acid applied with a swab to free the surface of the copper from oxides or impurities, then rub the ball of amalgam over the surface, using some little force. It is always well when copper-plates are coated with silver or zinc by means of mercury to let them stand dry for a day or two before using, as the mercury oxidises and the coating metal more closely adheres.