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GRADING   PIG   IRON   BY   ANALYSES.                  153
than the 3.00 per cent, of silicon shown in Table 22.
It is not to be understood by the above that no attention is to be paid to the manganese, phosphorus, or total carbon when ordering iron by numbers, as in Table 22. In some cases such will be very necessary, as one founder may require very high or low manganese, phosphorus, or total carbon, while another may stand a wide variation in these elements as long as the silicon and sulphur are best suited for the work. To designate the manganese, phosphorus, or total carbon in any system of grading by analysis in numbers, that is intended for universal use, could meet with little favor for the reason that furnacemen cannot vary these in unison with variations of silicon and sulphur in obtaining different grades.
The manganese, phosphorus, and total carbon, the author believes, will be found to be best omitted from any universal system of numbering grades. "When a founder desires any special percentages in one or all of these three elements in purchasing foundry, bessemer, gray forge, mill, or basic irons, he can designate just what he would like, aside from stating the number of the grade desired, and if he cannot get what he desires at one furnace he will have to try others. The manganese phosphorus, and total carbon will not, as a rule (as shown in Chapter XVII.), vary to any injurious extent for the general run of ordinary castings, in any one brand of iron made from like ores, fuels, and fluxes, in irons having less than 4.00 of silicon, as the silicon and sulphur can; and hence the reason why the author suggests confining grading by analysis in numbers to the silicon and sulphur, as seen in Table 22. The class of castings in which it is generally mostunchilled 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     "