From the viewpoint of malleability, malleable iron may be considered to occupy a position between gray cast iron and steel. Photomicrographs Nos. 109 and 35 are those of malleable iron before and after the annealing treatment. The former shows the typical structure of _white cast iron_, while the latter plainly shows the minute lumps of pure carbon and the surrounding grains of pure iron metal, the two having become divorced through the annealing process. Note that the large amount of carbon in this, the “temper carbon” form, does not make the alloy brittle through cutting of the grains as does the crystalline graphite form of carbon. The above gives very briefly the most essential points in the classification of the irons and steels from the structural standpoint. True it has not entered into the vast complications of the higher carbon or tool steels which are those which will take a “temper”; i.e., the tool steel’s quality of hardening by quenching in water from a cherry red heat. The simpler points of these will be taken up later. But enough has been given that we now understand something of the relative positions of the great main products, some reasons therefor, and their general structures. [Illustration: NO. 8. BAR ROLLED FROM SCRAP; CONTAINS BOTH WROUGHT IRON AND STEEL ] It has been seen that their micrographs quite definitely differentiate them and probably no one will have difficulty in recognizing and naming such specimens. As testing this it may be interesting to note photomicrograph No. 8. Two different iron alloys made up the material from which this photomicrograph was taken. Apparently the bar was one made by heating and rolling together scrap metals. Such material is on the market. The photomicrograph shows that some of the scrap used was wrought iron and some of it mild steel of about .08% carbon. Classification by Chemical Analysis and by Physical Tests So far not much has been said about composition except that upon it to a great extent depends the structure and physical properties of the alloy. Composition and physical characteristics as well as structures are necessary to a fair TABLE B—CHEMICAL COMPOSITION AND PHYSICAL PROPERTIES