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2l6                      METALLURGY   OF   CAST   IRON.
Over 0.75 per cent, of phosphorus can cause iron to be '' cold short,'' which means brittle when cold, and it may harden iron if used in excess of 1.30 in castings.
By keeping phosphorus down to between 0.20 and 0.40, with silicon from 2.50 to 2.75 and sulphur about .05, thin castings can often be made so as to bend considerably before breaking, and also admit of cast iron being readily punched with holes, similarly in some degree as wrought iron would be affected by like treatment. It has been contended that phosphorus is in no wise beneficial to the strength of an iron, but Woolwich's experiments would show that phosphorus running from about 0.20 to 0.50 is beneficial in improving the ductile qualities in physical tests for cast iron work. Phosphorus is chiefly obtained from the ore and flux. It retards the saturation of iron for carbon and adds fluidity and life to metal. It is the most weakening element iron can possess when used in excess, and is often objectionable when it exceeds i.oo per cent, in Foundry iron, in which it is best kept down to not exceed .80. Necessity for extra fluidity, or life, to the liquid metal is the only occasion where phosphorus should be permitted to exceed . So in Foundry iron.
While phosphorus is an element very essential to the success of founding, it generally needs to be guarded as closely as sulphur or silicon, and an intelligent use of it will prove that it can strongly influence mixtures and the life and wear of castings. The author takes pleasure in citing here some experiences of Mr. James A. Beckett, of Hoosick Falls, N. Y., in experimenting in a practical way with phosphorus as an agent to regulate actual mixturesII.