86 Mr. D. Musliet on ihe Crystullizaiiun of' Iron. 



the upiier part of the head broken off by means of a large 

 hammer. This will generally be followed by a fine display of 

 crj'stallized iron, ofevery variety of colour; or, if the coloured 

 crystals should be scarce, they can readily be made from the 

 silvery colouretl ones, by heating them in a vessel in a bright 

 fire, till the summits of the pyramids begin to change colour. 

 The specimen is then thrown out, and will be found, when 

 cold, possessed of every shade of colour of which polished iron 

 or steel is susceptible. 



Cells of colourless crystals resembling frosted silver are 

 sometimes observed in large castings, opposite to the runner 

 or feeder, which seem to differ from the other crystals merely 

 in their formation having taken place under circumstances 

 whei'e atmospheric air has been totally excluded. The less 

 carbon in the iron, the purer the colour and the more perfect 

 the form of the crystal ; and this observation may be extended 

 to all crystals of cast-iron in general. 



Wlien cast-iron is run from the blast furnace and becomes 

 covered with a quantity of the fluid slag, the surface of such 

 iron is sometimes found to possess a linear chequered crystal- 

 lization, in which are stems of the more perfect pyramid, 

 but of an imperfect form like the letter =1 with feathery lines 

 across, and but little relieved from the plane of the metal. 

 Iron cooled slowly in this case communicates the most beau- 

 tiful prismatic colours to the slags, of a deeper and more de- 

 termmate dye than the surface colours before alluded to. 



If Swedish or Russian malleable iron, both of which con- 

 tain more carbon than English iron, are melted in a crucible, 

 they will cool with a slightly radiated convex upper surface, 

 and a smooth under surface with the convexity increased. If 

 the same irons are melted under glass containing an alkaline 

 mixture, both their upper and under surfaces become beauti- 

 fully crystallized. If the carbon predominates, as is the case 

 in some of the Swedish steel irons, the under sm-face will pi'e- 

 sent small crystallized concaves, in which the rudiments of the 

 octahedron may be found. 



Englisli malleable iron, when melted, cools in flat buttons 

 with a smooth upper and under surface ; but when melted with 

 from one to two j)c') cent, of carbon, the cooling becomes more 

 convex on both sides, and crystallization ensues ; in point of 

 form similar to that which takes place with foreign iron, but 

 with a less splendid metallic surface. The grain of the frac- 

 ture of cast or melted malleable iron varies with every change 

 of temperature. If it is melted in a heat merely sufficient for 

 its fusion, the grain will be small and tough, and the iron will 

 draw at a icd heat under the hammer. Every shade of heat 



beyond 



