370 Mr. Mallet on the Physical Conditions 



The Plate illustrates the principal states of molecular condition, in which cast-iron and 

 wrought-iron respectively are found; as in every mineral substance, nothing tut actual 

 observation of specimens can give complete or accurate knowledge of either the aspect or 

 properties of iron. To those less practically conversant with the subject, these figures will, 

 however, afford the means of understanding more fully the text, and give a clue to the 

 identification of the several molecular conditions of iron when actually met with. 



The figures bear reference to the subjects discussed in Chaps. 3, 4, 5, 6, 7, 22, 23, 24, 

 25, and 26 of the text, and in this and other Notes. 



Figs. 3, 4, 5, 6, and 7, relate to cast-iron. Figs. 1 and 2, to wrought or malleable iron. 

 They are all drawn to one-half (linear) the natural size. 



Fig. 3 represents a fragment broken oflTfrom a refinery pig, of Styrian cast-iron (Spie- 

 geleisen), the top of the figure being the upper side of the flat slab, of about 4 in. thick, 

 18 in. wide, and some feet in length, when cast; and the lower side of the figure, the 

 bottom of the pig, which is usually cast in iron or " chill" moulds, and cooled also by 

 affusion of water, when intended for conversion into wrought-iron afterwards ; hence called 

 " Refinery Pig." 



This may be considered as the normal type of cast-iron — consisting of iron with fre- 

 quently above 5 per cent, of carbon, the whole of which is in chemical combination 

 with the iron, which hence contains no graphite. The mass is, therefore, perfectly 

 homogeneous in constitution; is of a bright silvery-white colour; the fracture proves it 

 highly crystalline, the crystals being very large and perfectly defined, often some inches 

 long, cleaving with perfect faces and angles, and the hardness so great that a cast-steel file 

 with difficulty abrades the mass. 



It will be remarked, that the principal axes of the crystals are all approximately per- 

 pendicular to the top and bottom of the slab, i. e. to its cooling surfaces, in accordance with 

 the general law. All " chilled" cast-iron approaches more or less to this normal type. 



Fig. 6 is a pig of Acadian or Nova Scotia cast-iron, presenting the usual characteristics 

 of that form of pig-iron known in Great Britain as No. 4 pig. It is closely allied in chemical 

 constitution to the preceding, but usually contains more or less uncombined carbon, in the 

 state of minutely diSiised graphite, not visible to the naked eye, but communicating a 

 slight dulness or grayish shade to its otherwise silvery lustre. Although the fracture 

 drawn here is nearly square, the general form of the pig was irregularly roundish, or 

 cyhndric, with one flattish side — hence the principal axes of the crystals radiate from a 

 central point, in accordance with the general law. The crystalline structure of No. 4 pig 

 is never very perfectly developed ; it is usually more or less lamellar in fracture, some- 

 times almost perfectly uniform or glassy in fracture, and, except for refining into bar-iron, 

 or mixing with more graphitic cast-irons, is useless to the founder, being brittle and 

 intensely hard when cold, requiring the highest temperature of all cast-iron for fusion, and 



