Galvanised Iron.

Galvanised Iron. This name is given to iron which has been coated with zinc to prevent its rusting. The iron is simply dipped in the melted zinc, and the name does not imply, as might be supposed, that any definite galvanic process is undergone. Galvanised iron first came into use about 1837, when iron cooking-vessels were treated in this way. Since then tinned iron has come into use for cooking-vessels, and galvanised iron is now employed chiefly for roofing purposes, buckets, telegraph wire, chains, &c. The process of manufacture is very simple. The zinc is melted, and dry sal-ammoniac poured on the top. This fuses and forms a protecting layer, keeping the surface of the metal clean. The iron plates or vessels, having been carefully cleansed by means of dilute hydrochloric acid and scrubbing with sand, are now introduced into the molten zinc, which immediately forms an alloy with the iron, and renders it incapable of rusting. Care must be taken not to immerse the iron for too long a time, for the alloy of zinc and iron melts at a comparatively low temperature, and there is a danger of destroying the vessel which is being galvanised. Galvanised iron is not so tough as iron itself, but still the freedom from rusting makes it specially applicable for many purposes. Galvanised iron water-pipes are now much employed in houses, but steam-pipes of this material are unsatisfactory: when exposed continuously to a moist steam heat, galvanised iron seems to become corroded, and small holes make their appearance. Galvanised iron is, of course, unsuitable where any acid is present, and any preparation containing vinegar will assume a disagreeable taste if placed in a galvanised vessel.