Semi-steel is a very close-grained alloy of ten or twelve thousand pounds per square inch greater strength than cast iron. It is a most satisfactory material for medium and larger sized castings for which cast iron formerly was used. [Illustration: CAST IRON TEE, COCK PLUGS, AND RETURN BENDS, WITH SPRUES AND GATES ATTACHED ] Did we say that cast iron was very brittle? So it is, comparatively speaking. But just as the chemist will tell you that there are no substances which are absolutely insoluble, just so does cast iron appear to be extremely brittle only when compared with the iron alloys of considerably less brittleness. The three pictures of the hooped and twisted casting illustrate how unwise it might be to speak with absoluteness. A few years ago the casting illustrated on pages 190 and 192 was brought to this country by a visitor to Europe, with an expression of regret that cast iron produced in this country did not have such qualities of elasticity as had cast iron made abroad. Whereupon, without any change whatever in his iron mixture or cupola practice, the superintendent of a well-known foundry made castings which were exact duplicates of that submitted. The three photographs shown further on (Figs. A, B, C) were of one of these castings. The ability to bend without breaking is, of course, largely due to the shape. [Illustration: PLUGS AND WHEELS AS THEY COME FROM THE MOLD Occasionally as many as 200 castings can be made in one mold. ] [Illustration: TYPE OF MOLDING MACHINE ] As a matter of fact, such castings were not at all new in this country, having been furnished by American foundries for electrical work for many years. Cast iron springs, piston rings, and many other articles of cast iron are regularly made, which show such elastic quality. We have said considerable about “castings.” In general we know what castings are, but in the minds of some there may be a little uncertainty as to the manner in which they are produced. [Illustration: ANOTHER OF THE MANY KINDS OF MOLDING MACHINES ] There are few lines of human endeavor which require greater judgment and skill than does the making of molds for castings. Sound judgment based on long experience, knowledge of conditions under which the work immediately in hand must be done, observation, and accurate, deductive reasoning as to the causes of failure are absolutely necessary for success. [Illustration: CASTING, WHICH BECAUSE OF ITS LENGTH AND SMALL CROSS SECTIONS, REQUIRES VERY FLUID CAST IRON. (FIG. A) ]