54 JOURNAL AND PROCREDlNGvS. 



carbon is almost entirely in chemical combination with the 

 iron, much as it is in the case of steel. During the anneal, 

 however, this state of combination is broken down and the 

 carbon becomes separated, and appears in a verj' fine state of 

 subdivision between the grains of the metal. It is this 

 separated carbon which is tlie cause of the color of the 

 fracture, and its appearance is a condition of a material of 

 satisfactor)^ character. It is therefore customary to judge 

 malleable iron partly by tlie appearance of the fracture, and 

 it serves, under experienced observation, as a reliable indica- 

 tion of quality. 



This separation of the carbon and the physical trans- 

 formations which accompau)' it are the essential features of 

 the anneal, but under regular manufacturing conditions two 

 other changes of a minor character also occur. These are the 

 oxidation and consequent removal of the carbon from the 

 surface of the casting inward, and a gradual absorption of 

 sulphur from the material of the packing and the gases of 

 combustion. The removal of the carbon is due to the nature 

 of the packing, which is composed largely of oxides, and 

 which gives up its oxygen to the carbon at the elevated 

 temperature of the ovens, while the absorption of the sulphur 

 arises from the affinity of the iron for that element under the 

 same conditions. The Silicon, Phosphorus and Manganese re- 

 main practically unchanged in quantity whatever modifica- 

 tions may occur in their state of combination. 



To illustrate the changes in composition which take 

 place in the annealing oven, we give in Table 5 the com- 

 position of the white iron, and of samples taken from bars one 

 inch square, at the close of the regular anneal. Four samples 

 were taken from the test bar, the first representing the iron 

 of the outer layer, one-sixteenth inch in depth, and the other 

 samples successive layers, each being nearer the centre of the 

 bar by one-sixteenth inch than the preceding : 



