I think that this observation explains the cause of many obscure flaws found in castings, sometimes causing them to break when subjected to quite moderate strains.  We frequently find little “cold shot,” or metallic globules, embedded in cast iron or steel, impairing the strength of the metal, and it has long been asked, “What is the cause of this defect?” The pellicles have been carefully analyzed, under the supposition that they might be alloys of iron and nickel, or some other refractory metal, but the analysis has failed to substantiate this theory.  Is it not probable that in the process of casting, little drops of molten metal are sometimes splashed out of the stream, which immediately solidify and become coated with a skin of oxide, then falling back into the stream of rapidly cooling metal, they do not remelt, neither do they weld or amalgamate with the mass, owing to this protective coating, thus forming dangerous flaws in the casting?

The process of carbonizing the delicate fabrics, leaves, grasses, etc., is as follows:  The objects are placed in a cast iron box, the bottom of which is covered with a layer of powdered charcoal or other form of carbon, then another layer of carbon dust is sprinkled over them, and the box is covered with a close fitting lid.  The box is next heated gradually in an oven, to drive off moisture, and the temperature slowly raised until the escape of blue smoke from under the lid ceases.  The heat is then increased until the box becomes white hot.  It is kept in this glowing condition for at least two hours.  It is then removed from the fire, allowed to cool, and the contents are tested in a gas flame.  If they have been thoroughly carbonized, they will not glow when removed from the flame, and the fibers may even be heated white hot before consuming.

Of course, the method employed to carbonize the materials is suspectible of variation, but the scientific principles involved are unchangeable, viz.: 

(1) Partial exclusion of air and substitution therefor of a carbon atmosphere.

(2) Slow heating to drive off moisture and volatile elements.

(3) Intense and prolonged heating of the partly charred objects to eliminate remaining foreign elements, and to change the carbon from the combustible form of ordinary charcoal to a highly refractory condition.

[Illustration]

NOTE.—­Fig. 1 is photographed from a white iron casting made upon carbonized coarse lace; the lower portion of the plate shows the lace embedded in the iron.  Fig. 2 is a casting in gray iron upon lace laid on an iron plate.  Fig. 3 is a casting in hard iron upon lace laid on dand.  Fig. 4 is a casting in gray iron upon a piece of thin summer dress goods with machine embroidery.

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RECENT PROGRESS IN GAS ENGINEERING.

At the recent meeting of Scottish gas managers Mr. A. Macpherson, of Kirkcaldy, the chairman, said: