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150                       METALLURGY   OF   CAST   IRON.
grade, as, for example, an iron with 2.75 per cent, of silicon and but ,01 of sulphur would give nearly as soft a casting as one that might contain 3.00 silicon with . 04 sulphur, and which is a system upon which all the various grades seen in Table 22, page 152, are divided.
Great interest was manifested in the subject of this chapter at the American Foundrymen's Association Convention in 1901 and several plans, aside from the author's, were presented. A committee was appointed, with the author as chairman, to continue the work and report progress at the convention to be held in 1902. It is with a view of assisting this work as much as possible that the author presents this chapter, and he would like to publish all the methods presented at the convention did space permit. However, any one desiring to read what others presented to the convention on the subject can do so by procuring copies of the American Foundrymen's Association Journal for July, or the Iron Trade Review of June 13, 1901.
The author's extended experience, obtained by closely following variations in the hardness of castings or test bars due to changes in silicon and sulphur, with the other elements fairly constant, is such that he can safely say that where sulphur is kept constant every increase of .25 per cent, silicon should change the grade of pig iron one number in all iron ranging to 3.00 or 4.00 per cent, in silicon. It takes less sulphur than any other element to effect a change in the grade or hardness of a casting. A change of one point of sulphur (.01) can often neutralize the effect of eight to fifteen points of silicon. This will be better understood by referringoften be required at the highest point of any oneled as well as unchilled castings. analysis which may be given is simply an average of the whole, generally taken from the two ends andith the uncertainty of furnace workings when in urgent need of ten hundred             jon of iron; and Sir........................    2,720     "