Cast Iro?i, Steel, and Malleable Iron. 425 



rangement in nodal aggregations begins to be developed in 

 tilted but softened best cast steel and in white cast iron ; but in 

 their most perfectly equal division throughout the whole mass 

 of the iron, without any certain relative position of their sur- 

 faces, they appear in tilted but hardened cast steel of the high- 

 est conversion, and for their looser and more irregular, and in 

 large masses fibrous arrangements, are the different species of 

 malleable iron, the fairest specimens. 



Some time since graphite was considered mechanically 

 mixed with the mass of steel; and in consequence of this 

 theory, it was asserted by many writers on the subject, that 

 the graphite scales might be seen in the fractures of steel and 

 intimately intermixed with it, even with the naked eye. Now 

 it is perfectly well known that no such scales can be discover- 

 ed in any steel whatever; but in gray cast iron its peculiar 

 appearance is still explained to be derived from the scales of 

 graphite, notwithstanding the impossibility of discovering it 

 by the highest magnifying power. 



The glittering scale-like particles which appear in the frac- 

 ture of gray cast iron are, in fact, the sides or faces of a cry- 

 stalline figure, and those perfectly flat sides are divided regu- 

 larly by their higher crystalline orders, into trapeziums or 

 pentagons, the diameter of the most regular being about 

 0'000355 of an inch, those of the greatest length being 

 about three times their width; and those pentagons are again 

 found to be composed of the above-mentioned molecules of 

 only 0*0000633 of an inch diameter ; but no scales which 

 could interrupt the regular arrangement of those molecules 

 can be perceived. 



A fragment of such very gray cast iron under a microscope 

 resembles much a fragment of some anthracite of South 

 Wales, both as regards its fracture and colour ; and the forms 

 of imperfect prisms are never to be mistaken in the whole 

 formation. 



In the cross fracture of hardened cast steel (of a razor 

 forged in my presence in the factory of Messrs. Rogers of 

 Sheffield) it appeared milky white, somewhat like deadened 

 silver. By the aid of a microscope the molecules appeared 

 equally distributed, and their facettes never in one plane, so 

 that the whole fracture, in the field of a microscope, appears 

 to be composed of innumerable bright points, the plane some- 

 times interrupted by elongated furrows, in which may be dis- 

 covered the angles of deeper situated points, the whole having 

 a somewhat similar appearance to the full moon when first 

 viewed through a common telescope. 



I took the other parts of this fractured razor, heated it care- 



