426 Dr. Schaf haeutl on the Different Species of 



fully to a light red heat, and suffered it to cool slowly. Being 

 then broken again, the milk-white earthy fracture was now 

 changed to a more distinct granulated, and a more blueish 

 metallic surface. Under the microscope this surface had lost 

 its eqiiality of the disposition of the molecules ; several mole- 

 cules had now aggregated together, having their bright faces 

 all in one plane, and approaching in form the facettes of gray 

 iron. The whole surface of the fracture was spread over with 

 such nests or bundles of crystals, and the furrows between 

 them appeared to be much widened. 



These striking differences between hardened and soft cast 

 steel appear to me to explain at once the great hardness of 

 cast steel dipped red-hot into water, and its property of not 

 being acted upon by the file. 



It is well known that the power of mutual attraction between 

 molecules is almost irresistible, and it follows that when once the 

 equilibrium of a liquid mass is destroyed different centres of 

 attraction ai'e forming themselves, towards which the nearest 

 molecules move, grouping themselves around it, and assuming 

 a geometrical form according to their original shape. In this 

 crystalline form the molecules are in a state of equilibrium, 

 and their equilibrium is stable in both respects; but the power 

 of cohesion acting from different centres, and in certain di- 

 rections, it is the greatest only in the central points of crystals 

 and approaching to the axis of crystallization, and the mutual 

 attraction or cohesion of those crystalline bodies thus formed 

 is infinitely weaker than the internal central cohesive force of 

 the molecules, which constitute those crystalline aggregates. 

 So in a somewhat similar manner, the hardest of all bodies, 

 the diamond, is very easy to be cleaved parallel to the faces of 

 the primary form of its crystal. 



Now when caloric enters into such a crystallized body, the 

 relative distance between the molecules increases, the stability 

 of the equilibrium in respect to position is decreasing ; there- 

 fore the form of the molecules begins to lose its influence, in 

 the same ratio as the equilibrium in respect of distance pre- 

 ponderates, thus dividing and acting on the molecules with 

 ■perfect equality througliout the "whole tnass. 



Suppose now we abstract suddenly the caloric before the 

 relative attractive force of the molecules has time to arrange 

 them perfectly in an equilibrium of position; all the irresist- 

 ible powers of attraction are revived and restored: the mole- 

 cules will therefore attract each other with equal force 

 throughout the whole mass, and consequently there appears 

 no reason why any body, formed of the same material, and 

 under the same equally powerful influences of equal molecular 



