EFFECT OF VARIATIONS IN TOTAL CARBON. 247
in the percentages of carbon in iron cannot be controlled sufficiently to regulate mixtures in everyday founding. This proposition is largely due to some advocating that the creation of the graphitic carbon is not regulated by silicon, but due chiefly to changes in the percentages of carbon. It is true that the higher the carbon, the more graphite there is in normally made and cooled pig iron or castings, other conditions being equal. Nevertheless, variations in the silicon and sulphur, especially the silicon, are chiefly responsible for variations in the graphite of different pig or castings. If those who think otherwise will take note of variations in the total carbon and the combined carbon they will find that, allowing for changes in the percentage of total carbon, the combined carbon varies closely with those of silicon and sulphur, especially the former; or, in other words, with a constant total carbon, sulphur, and manganese, etc., the higher the silicon, the lower the combined carbon and the higher the graphite, in normally made and cooled pig iron or castings.
flalleable founders notice that the heat of irons is greatly derived from the carbon in it. As a rule the low silicon irons give them the highest carbon. When the exception to this rule takes place and they get low carbon in low silicon irons, which many prefer, they notice its heat effect in a very pronounced manner. Iron with less than i per cent, silicon may have carbon up to 4.50 per cent, while over 4.00 per cent, silicon iron may often not exceed 2.00 per cent, carbon.
To insure good fluidity it is not to be understood, by the above, that it is necessary to have carbon above 3.75. To obtain good fluidity, extra silicon, phosphorus, and often manganese are necessary to be com-o.n. in ladle 1,772 Ibs. .100" -326 " I.IOO .242 3