MECHANICS AND USEFUL ARTS. 33 



able. There are certain kinds of strong, hard iron, which, when melted and 

 suddenly brought in contact with a cold metallic surface, will " chill; " a 

 stratum of the iron about half an inch thick will be converted into white, 

 fine-drained surface, of such extreme hardness that ordinary tiles and drills 

 will make no mark on it. Such iron is poured into moulds, of which the 

 part touching the tread of the wheel is a ring of metal, which chills the sur- 

 face, the rest of the wheel cools more gradually, and is only a little hard- 

 ened, for " chilling iron " always hardens when recast so much so, that 

 new admixtures of pig-iron must be added, or it will become too brittle and 

 " short " for wheels. But the wheel, while cooling, contracts unequally, 

 since the thickness of its parts are different, leaving a severe and permanent 

 strain an inherent tendency to fly to pieces, which the roughing of our 

 roads does not ameliorate. To make a shape, by means of corrugations of 

 innumerable forms and directions, that will allow the parts to yield to this 

 coTitracting force while cooling, so that no strain shall be left in the wheel, 

 has been the subject of hundreds of patents. Again, the "chilling iron" 

 that must be used for the tread is too hard and brittle to answer the best 

 purpose for the rest of the wheel, while the softer and tougher irons that are 

 best to resist strains will not chill; so a single casting cannot fulfil every 

 desirable condition. 



It has long been the custom of some lines to use chilled cast-iron tires on 

 locomotive driving-wheels. They are much harder than wrought tires, and 

 wear better; they are not so truly round as wrought iron or steel tires, which 

 are turned in a lathe; their adhesion is less, and they are very heavy and 

 hard on the track. Yet they are very much cheaper than wrought iron, not 

 to speak of steel. Considering their immense weight, their economy in the 

 long run is questionable. But this chief objection has been partially ob- 

 viated by Mr. H. W. Moore, of the Union Car-Wheel Works, Jersey City, 

 who has perfected a process of casting the tire hollow, thus reducing the 

 weight of a four and a half feet tire from one thousand pounds to seven 

 hundred and twenty pounds, and at the same time preserving its strength, 

 if not increasing its soundness. 



All these facts bring us to the consideration of Mr. Moore's improved car- 

 wheel, which is simply a nave or centre-piece of tough, strong cast iron, and 

 a hollow, tire of hard chilling iron. The two, when fastened together by the 

 very simple process used in fastening the same kind of tire to driving- 

 wheels, form a complete cast-iron wheel, which possesses the following very 

 obvious and very important advantages : First, The nave, or centre-plate, 

 never wears out, it being practically a part of the axle. When a common 

 wheel is worn out, the whole of it is used up, and, being all of " chilling 

 iron," cannot be recast into wheels without a large admixture of pig-iron. 

 With the new wheel, the tire only is removed when it wears out. Second, 

 The nave, being subject to no wear whatever, may outlast the axle, and be 

 fitted to new axles as the latter wear out. Third, Tire nave may be made of 

 softer iron than the tread or tire requires, and so be less liable to breakage. 

 Fourth, The tire may be of harder iron than is required for the nave, and so 

 chill deeper and harder, and wear longer. Fifth, The wheel as a whole is 

 stronger, no strain being left in it by the unequal contraction of the metal 

 as it cools. As before mentioned, the great trouble has been that the quickly 

 cooling tire and the thicker and slower cooling hub cause a severe and per- 

 manent rupturing force to be left in the wheel when it is a single casting. 

 In this case, the thin, hollow tire cools without strain, and the nave may bo 



