210 METALLURGY OF CAST IRON.
sulphur did not exceed .022. This is a good example in illustration of the effect of sulphur in hardening iron, for had the sulphur been .07, as is generally the case as an average for light castings in America, 'with the silicon only .55, such castings would be so hard or "white," that they would never hold together long enough for one to handle them. The low sulphur in the Russian castings would lead us to say that they were made from cold blast charcoal iron. *
Silicon can be absorbed by iron to as high as 20 per cent., and from 3 to 4 per cent, of silicon in mixture will generally change all the carbon found in ordinary irons to graphite that it is possible to change. The percentage it will require to do this is dependent upon the percentage of the other constituents present in the mixture. Silicon ranges from i to 5 per cent in Foundry iron, in standard Bessemer iron from i to 2^/2, per cent., and in ferro-silicon pig iron from 5 to 14 per cent. In making mixtures of iron with pig containing 4 to 6 per cent, of silicon there is far less risk of over- dosing a mixture than with pig containing from 8 to 14 per cent, of silicon, for although we may figure out to a nicety just the percentage pig may contain and direct how many pounds should be charged, it cannot but be seen that with the higher percentage of silicon pig the least error in weighing it, etc., could be very disastrous in results. In cases where a founder has a cheap class of work and desires to use all the scrap, burnt or hard iron possible, he may often use
* The Russian analysis was obtained by Mr. H. L. Hollis, of Chicago, and presented in a table with other analyses of American castings in a paper read before the Western Foundrymen's Association, May, 1894.a fluid state, see Chapter LX, and the carbons, etc., in iron, as