47 



rolled, and very much stronger, or as 28 to 24^. The increased 

 strength in the mixture of wrought and cast iron, called toughened 

 cast-iron, renders it peculiarly adapted for wheels, pinions, &c., and 

 for girders, columns, and other architectural uses. Several govern- 

 ment works so constructed — the Chelsea, the Windsor, and the 

 Yarmouth Bridges — also, at various iron-works, all rolls, pinions, 

 and cog-wheels are made of it. The wrought-iron made either 

 from the toughened cast, or by the admixture of calamine, is par- 

 ticularly useful for tension rods, chain-cables, &c. The addition of 

 antimony and some other metals to wrought-iron in the puddling 

 furnace gives a hard and crystalline iron, nearly allied to steel in 

 some of its properties, and is adapted, from its hardness and crystal- 

 line character, to form the upper part of railway rails and the outer 

 surface of wheels. When thus united to the iron containing zinc, 

 the best sort of rail results, combining strength, stiffness, and hardness 

 with anti-laminating properties, and being also cheaper than any 

 other kind of hardened rail or tire. Compounds of copper, iron, 

 and zinc are found to be much closer in texture, and stronger than 

 similar compounds of copper and zinc (the proportion of iron not 

 usually exceeding 1^ per cent.), and can be advantageously used as 

 substitutes for gun-metal, under all circumstances, for great guns, 

 screws, propellers, mill brasses, and railway bearings ; small addi- 

 tions of tin and other metals alter the character of these compounds, 

 and render them extremely manageable as regards hardness and 

 stiffness. The advantages which these compounds possess over gun- 

 metal are cheapness and increased strength, being about one-fourth 

 cheaper, and one-half stronger, and wearing much longer under fric- 

 tion. On many railways, the alloys of zinc, iron, copper, tin, &c., 

 have superseded gun-metal for carriage bearings. An alloy equal 

 in tone to bell-metal, cheaper, and at the same time stronger, is 

 made from the alloy of copper, zinc, and iron, a certain proportion 

 of tin being added. The addition of iron seems, under most, if not 

 all circumstances, to alter the texture of metallic alloys, rendering 

 it closer, and the alloys, therefore, more susceptible of a high polish, 

 and less liable to corrosion. Other alloys of iron were exhibited, 

 some shewing the extreme closeness of texture, others possessing 

 very great hardness, and suitable for tools, cutting instruments, &c., 

 others possessing a high degree of sonorousness. A bell was ex- 

 hibited, of fine tone ; its advantages being cheapness (less than half 



