ELEMENTS DESIRABLE FOR ELECTRICAL WORK. 285
making mixtures for castings expected to convey electric currents.
It will be seen that the silicon in the above analysis Is as high as 3.190, a point rarely attained in other specialties of casting, but it will be noticed that the sulphur is also well up, so that it greatly neutralizes the softening effect of the silicon. If the sulphur were about .050, the same softness would be obtained with about 2.60 of silicon, so powerful is the effect of a few points in sulphur to promote combined carbon.
In testing a casting to discover its degree of softness by analysis, it is usually best to first find its percentage of combined carbon, which should not exceed .70 and is best kept down, if possible, to about .30. If an analysis shows the combined carbon to be too high, then determinations should be made of the sulphur and silicon contents of the iron, to learn if cither of these elements is at fault, as these properties are the bases in changing the " grade Vf of iron to control, the carbon in taking the graphitic or combined form. The higher the carbon, and the more it is thrown into the graphitic form, the better the iron for electric work.
The effect of high phosphorus is to slightly retard softness, and for this reason it is also best kept us low as is consistent in obtaining the fluidity desired. Phosphorus should not exceed .80, unless some very thin eastings are to be made, or there are parts in heavy eastings difficult to u run; " then phosphorus may be allowed to approach i.oo.
Manganese in iron for electric work is also a factor which requires watching, as its tendency is to promote hardness or combined carbon. It is best not to exceed .40, unless the silicon is over 3.00 and themake gun iron castings in the cupola that 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-