MIXTURES FOR WHITE IRON CASTINGS, ETC. 289
small castings. The oxide withdraws carbon and what remains exists mainly as temper carbon or, as more commonly called, graphitic carbon. The decarbonizing of castings is greatest near the surface. The interior of thick castings often gives tip little if any carbon. This causes thin castings to appear much more malleable, or ductile, than thick ones. The reason of this will be better understood when it is stated, as shown by Dr. R. Molclenke, that in analyzing a fa-inch malleable casting with the ends broken off, which was placed in the shaper and i-i6-inch cuts taken off, the first cut analyzed .16 total carbon, the second.65, the third 1.84, the next 3.97, and the last 4.05 per cent. The original casting contained 4.08 per cent, of total carbon, thus shoAving that the interior of thick malleables may be but little changed. This has caused an impression that £4 of an inch was as thick as was practicable for good malleables. The process of annealing, lengthens castings to such an extent as to expand them about y& of an inch per foot. The lighter the casting, the relatively greater the expansion. This expansion greatly counteracts the excessive contraction which must be allowed in making patterns, and is such as to often call for no greater contraction than in making patterns for gray iron castings.
The percentage of silicon used for malleables to get white iron in castings ranges from .60 to 1.25, running* lower with the thickness. The iron for making malleables is melted in the cupola, air, and open-hearth furnaces. The cupola is generally used for light castings as it gives a better opportunity to obtain very fluid iron, which will permit its being carried in small ladles to the moulds, than that coming from furnacesthat would stand the tests of the United States Government for gun carriage work rightfully belongs to Messrs. Robert Poole & Son Co. of Baltimore, Md., and Muirkirk pig iron made by me. This was in 1893. The War Department at first refused to accept cupola iron as gun iron, but when it was fully demonstrateduois Iron Co., Illinois Steel Co., Jefferson Iron Co., Kittan-ning Iron & Steel Co., C. A. Kelly Plow Co., Lebanon Furnace, Longdale Iron Co., Lackawanna Iron & Steel Co., Logan Iron........................ 16,720 " t-