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GRADING   PIG   IRON   BY   ANALYSES.                  151
to Table 21 which shows, approximately, the increase in silicon and sulphur necessary to maintain a uniform hardness (or a fairly constant condition of the carbons) in re-melted pig iron that will not vary thirty points in manganese and fifteen points in phosphorus, a range that is within the limits of what generally exists In irons made from similar ores, fuels, and fluxes. In brief, Table 21 shows that if an iron containing 2.00 per cent, silicon should have its sulphur increased from .01 to .06, then in order to maintain an approximately equal hardness in similar test bars or castings the silicon would have to be increased fifty (.50) points. In coke irons, as a rule, the lower the silicon the higher
TABLE  21.
Sulphur       ..........	.01	.02	.03	Od		06
Silicon ................	2.00	2.10	2. 2O	2 30		
the sulphur will be found. In establishing standards the amount of sulphur, therefore, should be considered as well as the silicon. Recognizing this fact in connection with the statement above, which makes a distinction in grade at every .25 per cent, of silicon, Table 22 is presented by the author as a method for numbering grades, which,' if adopted, would greatly lessen the confusion and trouble we find the practice created previous to 1901.
By the method seen in Table 22, page 152, one can form some fair idea of the hardness to be expected in castings from pig iron, when ordering by number in different grades of iron. Then again, if adopted, it would give a fair knowledge of the value of an iron from a reading of the market reports of prices, by 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     "