(1) To prevent silverware from tarnishing, it is only necessary to brush it over with alcohol in which a little collodion has been dissolved. It dries immediately, leaving a thin transparent invisible covering on the silver, which can be removed at any time by dipping the article in hot water.
(2) Silver paper. This is not the thin ephemeral-looking paper which the French are fond of calling pelure d'oig-non, but a product discovered by a German pharmacist, and used, we are told, in some of the large towns for preserving silver from tarnish of all kinds. 6 parts ordinary caustic soda are dissolved in sufficient water, and the solution is diluted to 20° B. To this solution 4 parts oxide of zinc are added, and the liquor is boiled* until this oxide is dissolved. Sufficient water is now added to bring the solution down to 10° B. Thin paper or calico soaked in this solution and dried will effectually preserve the most highly polished silver from the tarnishing action of sulphuretted hydrogen, which is contained in appreciable quantities in the air of all densely-inhabited localities. Several journals have mentioned this preparation, but the exact manner of carrying it out is that given above from the German periodical in which it appeared. It is evident that not only silver objects may be preserved by this device for a considerable time, but scientific instruments made in other metals might be protected also during a long journey by sea or land from the oxidising influence of the damp air.
All that is necessary is to wrap up the articles completely in the paper, so that no external air can come in contact with them. (Burgoyne.) Zinc. - Damp air soon attacks zinc surfaces, but forms a film of oxide which arrests further corrosive action. Should the air, however, contain acid vapours, as it does in towns and near the sea, it is rapidly destructive. Soot is very injurious, forming a galvanic couple with the zinc, excited by the acid and watery vapour of the air. In contact with copper, iron, and lead, especially in the presence of moisture, voltaic action is also set up, and soon destroys the zinc This metal is also much affected by lime, even in the form of chalky water; and by all acids, organic not excepted, hence it should not be joined to oak nor placed where urine may reach it.