Metal Working Metals 29 



metal works easily. A well-made "fine" casting in iron is 

 as pleasant to work as any brass or gun-metal casting, and 

 with care can be made to look as handsome. Being tougher 

 than these metals, however, the labour expended in working 

 it is somewhat greater. 



Wrought Iron. This, the purest kind of iron chemically, 

 is most easily worked hot, when it may be hammered into any 

 desired shape. It is a useful exercise to heat " cut " nails in 

 a foot-blowpipe, and hammer these on a bench anvil into 

 staples, hooks, " riders " for levers, and other useful articles. 

 Wrought iron is usefully stocked in strips, J", f", and i" wide, 

 and of various gauges, from No. 18, ^j", to No. n, |". Six feet 

 of each kind will stock a laboratory for a long time, and will 

 prove extremely useful in a thousand ways in the repairing of 

 apparatus ; a simple example being to use such a strip for 

 binding together two broken pieces of an article such as a 

 galvanometer jacket, or even the mouth of a bell jar, two 

 co-incident holes being drilled in an iron strip at the lap, 

 and a suitable copper rivet inserted and riveted t up, or a small 

 bolt and nut being used. 



Steel is of several kinds, with widely differing properties. 

 Cast steel tool steel is perhaps the most useful, but mild 

 Bessemer steel is not to be despised, holding, as it does, an 

 intermediate place between cast steel and wrought iron. 



Tool steel has the great advantage that its hardness may 

 be altered to any desired degree. It may be softened to work, 

 and then hardened, if necessary, so that a tool will no longer 

 produce a scratch upon it. For this reason it is invaluable in 

 many instruments, particularly in parts subject to wear by 

 friction. 1 



Mild steel is less susceptible to " tempering," but not 

 altogether immune. It is tougher, less brittle, and easier to 

 work than cast steel, but it has not the tenacity, the hardness, 



1 To soften steel, it should be heated to a full red heat, kept so a few 

 moments, and allowed to cool slowly, either in the air, or in a bucket of 

 sand. To restore the hardness, heat to the same temperature, and plunge 

 into a bucket of water, or if great hardness is required, plunge into a vessel 

 containing olive oil. See also page 62. 



