AMERICAN INSTITUTE. 431 



water while it is hot, on removing it, it will be quite soft. The gong is 

 hairimered in the center only, to make it hard. 



Mr. Seeley. — The term " malleable iron," is only a new name for pure 

 iron. Iron, wrought iron, and soft iron, all mean the same thing. Steel 

 occupies an intermediate position between pure cast-iron and pure wrought 

 iron. Cast iron contains impurities which must be removed to give U3 

 wrought iron. Silicium and other impurities are removed by being 

 squeezed out in rolling and hammering, while the carbon is removed by 

 being burned out, in the process of reducing. The difference, then, between 

 wrought iron and cast iron, is that the one is pure, while the other con- 

 tains impureties. In the process of steel making, carbon seems to pene- 

 trate the iron in a strange manner. Particle after particle, passes into 

 the substance of the iron, and when about two per cent, of carbon has pen- 

 etrated the iron, we obtain steel. A larger proportion of carbon would 

 give us cast iron. 



It is a general law of metals that two fusible metals united give a com- 

 pound more fusible than either of the ingredients. Though carbon is not a 

 metal, yet the compound formed by uniting it with iron, is fusible. 



The passive state of iron is a remarkable condition. In ordinary cases, 

 iron is readily oxydized by acids, but, when touched by platinum it ceases 

 to be acted upon by the acid. 



Dr. Vanderweyde. — The passive state of iron is due to galvanic action, 

 and may be destroyed by heat, which restores the iron to its original state. 



Mr. Butler. — To drill chilled cast iron, the drill must be used hard as 

 it is taken out of the water. If it be put upon the grindstone to sharpen 

 it will not cut. 



Cast iron has been brazed. I have brazed wrought iron. Several years 

 ago a wheel was broken, which was hard to replace. I bound it together 

 with strips of iron, and placed very thin strips of wrought iron between the 

 faces of the fractures, after which I brazed it with common brazing solder, 

 and rendered it a good serviceable wheel. I am convinced that without 

 the strips of wrought iron between the parts of the fracture the brazing, 

 could not be done. 



Dr. Reuben. — The statements made in some of the previous remarks 

 seem to imply a contrast between chemical changes and molecular changes. 

 Also, the question was asked, "what is a molecular change ? 



I understand a chemical change to be a change of substance — an alter- 

 ation of inherent qualities. From oxygen and hydrogen to water, there is 

 a radical change of substance, but from water to ice or vapor there is not 

 such a change ; there is only a change in the mode of aggregation of the 

 particles. The same holds of the change from charcoal to diamond ; the 

 carbon particles are only aggregated differently in the two substances, but 

 the particles are identical in substance. These are instances of mole- 

 cular changes, which are wrongfully spoken of as the opposite to chemical 

 changes. They are not opposite to, but are included in the latter. The 

 word chemical should of right be opposed to j)hysicaL 



