250 Mr. Mallet on the Physical Conditions 



inch on the side, which he was able to detach from the interior of a bar of 

 wrought-iron which had long been at a white heat in an iron-smelting furnace, 

 and which were cleavable into smaller cubes and rectangular tables. They 

 contained about 2^ per cent, of silicium. 



208. With the same iron, and same volume of forging, however, the size of 

 crystal appears to be developed larger in proportion to the time that the mass is 

 maintained hot, and in process of forging. This time is necessarily greater, as the 

 mass is so, and as the operations of reducing it to required form, are more complex 

 or laborious. In fact, as in cast-iron we saw that the crystals were larger, the 

 longer the mass required to cool, — so in wrought-iron, they are larger, the longer 

 it is kept hot. And thus it happens that in very large and massive forgings, 

 requiring often to be maintained, perhaps for weeks, at temperatures, varying 

 from awelding heat down to dull redness, crystals are developed within the mass, 

 of a size materially to diminish, in some places, the average cohesion of the iron, 

 where their planes of cleavage produce partial " planes of weakness." The size of 

 these crystals is occasionally surprising, — the broadest and flattest planes of 

 cleavage frequently running in the directions in which surfaces of the integrant 

 " slabs" or portions of iron, of which the mass has been formed, have been 

 welded together. The author has observed crystals so posited, presenting flat 

 planes, as large as the surface of a half-crown piece, in forgings under seven 

 tons weight. 



209. Foreign charcoal-made iron, such as the Swedish, does not offer any ad- 

 vantage for ordnance over the best manufactured British wrought-iron. On the 

 contrary, Swedish iron, though strong and harsh, is most uneven and unequal 

 in quality, both as to strength and extensibility, — the same bar often presenting 

 various forms of fracture, at difi"erent points, or even united at every point, which 

 indeed must be expected, from the rude and imperfect mode of refining adopted 

 with it. The Low Moor iron, which, like the Bowling, is well known as one 

 of the finest makes in Great Britain, has been stated by Dr. Schafhaeutl (Phil. 

 Mag. vol. xvi.) to contain arsenic in appreciable quantity, indeed, nearly 1 per 

 cent. I am not aware if this curious circumstance has been verified as a general 

 fact by any other chemist. It is certainly unusual, and it would be interesting 

 to ascertain if it have any necessary connexion with the remarkable ductility 

 of the iron. 



