MECHANICS AND USEFUL ARTS. 35 



The force which holds together the molecules of iron is termed 

 cohesion. Teat will expand iron, and, when applied intensely and 

 continuously, will melt it, and will thus destroy all cohesion, and at 

 the same time all elasticity and all magnetic tension. It follows, 

 then, that heat of a certain degree is opposed to cohesion and elasti- 

 city. And this explains why large masses of wrought iron, when 

 being forged, and thus subjected for a considerable length of time 

 to an annealing process, will, in the centre, become greatly reduced 

 in cohesion and elasticity. The previously existing fibre in the faggots 

 will change into a coarse crystalline texture, because the iron being 

 in a pasty and nearly molten state, and the mechanical effect of ham- 

 mering being confined to the surface, and not penetrating to the centre, 

 the formation of large crystals will be left undisturbed. Broken car- 

 axles sometimes appear to have undergone a similar change. The 

 fact is that they generally exhibit a crystalline fracture. But I sus- 

 pect that many new axles, although manufactured out of fibrous rough- 

 bar, will, when finished and broken before they are used, also exhibit 

 a crystalline fracture. In my own practice I have witnessed the fact, 

 that an experienced manufacturer, anxious to satisfy me, did not suc- 

 ceed in manufacturing round bolt of four to five inches diameter out 

 of good fibrous rough-bar, without producing a crystalline texture in 

 the centre. The oftener he piled the iron, the worse the result. On 

 the other hand, I never heard of a failure when the bolt was forged 

 entire under the hammer out of good and well-worked and thoroughly- 

 hammered charcoal blooms, their rough ends cut off. 



The most fibrous bar iron may be - broken so as to present a granu- 

 lar and somewlfat crystalline fracture, and this without undergoing 

 any molecular change in the texture. Take a fibrous bar, say ten feet 

 long, but the longer the better, nip it in the centre all around with a cold 

 chisel, then poise the bar upon the short edge of a large anvil, and a short 

 piece of iron, placed eight or nine inches from the edge on the face of 

 the anvil, then strike a few heavy blows upon the nip, so that each 

 blow will cause the bar to rebound and to vibrate intensely, and the 

 result will be a granular and somewhat crystalline fracture. Now 

 take up the two halves, and nip them again all around, about one or 

 two inches off the fractured ends, break them off by easy blows over 

 the round edge of the anvil, and the fibre will appear again. This 

 experiment proves that a break, caused by sudden jars and intense 

 vibration, may show a granular and even crystalline fracture, without 

 having changed the molecular arrangement of the iron. All fibres are 

 composed of mineral crystals, drawn out and elongated or flattened ; 

 and the fracture may be produced so as to exhibit in the same bar, 

 and within the same inch of bar, either more fibre or more crystal. 

 But a coarse crystalline bar will, under no circumstances, exhibit 

 fibre ; nor will a well worked out fibre exhibit coarse crystals. 



My own view of the matter is, that a molecular change, or so called 

 granulation or crystallization, in consequence of vibration or tension, 

 or both combined, has in no instance been satisfactorily proved or 

 demonstrated by experiments. 



I further insist that crystallization in iron or any other metal can 

 never take place in a cold state. To form crystals at all, the metal 

 must be in a highly-heated or nearly a molten state. 



