AMERICAN INSTITUTE. 429 



fully understood. I believe it to be nothing more than iron which has 

 suiFered a molecular change. Carbon and nitrogen are doubtless elements, 

 essentially necessary to produce that change by their presence. 



Dr. Vanderweyde. — In Belgium, there are vast quantities of coal and 

 iron worked by an English firm, some of whose productions are worthy of 

 remark. I have specimens of their cast iron of remarkable toughness, ad- 

 mitting of their being readily bent. They are, however, non-elastic. This 

 extreme toughness, I attribute to freedom from sulphur and phosphorus. 

 Steel is not simply iron and carbon, it is something more which is not un- 

 derstood. In hardening, also, there occur changes which chemistry does 

 not explain. For instance, Indian steel is best hardened in the air. This 

 information I derive from the second volume of Berzelius on metals. I 

 may have been mistaken, and this may refer to Damascus steel. 



Mr. Tillman. — Cast iron chills by sudden cooling, and is evidently crys- 

 talline in structure. Is not that a molecular change ? If not, what is it ? 



Professor Hedrick. — It is difficult to understand how, in changing 

 wrought iron bars, by the old process, into steel, the carbon could mechan- 

 ically penetrate the iron. There must evidently be a chemical union 

 between the particles of the two elements. Now a change of specific heat, 

 indicates a chemical combination ; thus 28 parts of iron and 16 parts of 

 sulphur, would each require a certain amount of heat to raise their tem- 

 peratures through a certain number of degrees. When they have chemi- 

 cally combined to form sulphuret of iron, each compound atom will take 

 only as much heat as the single atom of either constituent. The phenomena 

 of latent heat are generally referred to chemical action, but it is not cor- 

 rect to refer them exclusively to this cause. It is true that chemical com- 

 bination is always attended with the evolution of heat, because, when two 

 or more atoms unite to form a compound atom, the latter acquires the 

 latent heat which its component atoms had previously possessed, and this 

 is more than it has capacity for, therefore the excess becomes sensible. 



Mr. Butler. — I think the changes are molecular, and that Mr. Tillman's 

 theory is the correct one. In my business, I hai'den steel in cold water, 

 and I believe that a piece of steel of considerable thickness could not be 

 hardened in the air, even if carried through it by the aid of a swift-horse. 

 Cast iron chills readily on being poured into proper forms, and, if pure and 

 fine it becoiies as hard as hardened steel. The crystalline appearance of 

 chilled iron is always manifest towards the centre. I use three kinds of 

 iron, known as Buckman, Scotch, and Crane, to ensure good castings. 

 Hard cast iron is close grained, and in drilling it the drill becomes highly 

 magnetic, much more so than in drilling hardened cast-steel The cutting 

 edge of the drill soon becomes polished and ceases altogether to cut. In 

 case-hardening, I have found that poor qualities of iron are soon convert- 

 ed, while the best rivet iron is more difficult to case-harden. I mention 

 the«e facts because much loss of time and materials is entailed by our not 

 having a record of the practical details of everyday business, without 

 ■which our foundry men have to work in the dark. 



