Page:A tour through the northern counties of England, and the borders of Scotland - Volume I.djvu/210

 Thames at Staines, upon a construction apparently superior to any hitherto cast. Indeed no doubt remains, that these iron bridges will supersede those of stone entirely; as they are put up with a fifth part of the expence, a tenth part of the time, and will be found to be equally, if not more, durable.

There is also belonging to Messrs. Walker a considerable manufactory for tinning iron plates, which are first drawn out 'to the requisite thickness by cylindrical rollers, and afterwards cut to the size required, and cleaned with a strong acid solution. They are then dipped into the tin, which is melted in a proper receiver, with a quantity of grease and resin on its surface, to prevent its calcination by exposure to the air, and the plate comes out with the tin adhering to it; this is afterwards cleaned and rubbed with bran to take off the grease, and is then compleated for use.

The conversion of iron into steel is also a considerable branch of the same manufactories. This is a simple process, by baking the hammered bars of iron in close ovens with charcoal for several days, till the carbo has completely penetrated the whole of the bar. In this operation the best and most malleable iron is used; and it seems as if this process only restored it nearly to its former state of cast-iron divested of its impurities; for as, in order