SEGREGATION OF IRON AT FURNACE AND FOUNDRY. 137
middle of a " cast," and that a car of iron may come to him from a " cast " having one portion from one-half to one per cent, higher in silicon than another. This is fully verified by Mr. Rubricius's table which shows that the two ends of a " cast " may vary one per cent, in silicon. Mr. Rubricius also states that " notwithstanding the large number of experiments made, it was not possible to correlate the initial percentage of silicon and the rate of increase, as iron poor in silicon presents, in some cases, a large increase in silicon in the upper parts. This can only be due to the difference in specific gravity between silicon and iron.''
The uneven distribution of silicon and sulphur in pig metal is largely due to conditions over which furnace managers have, as a rule, not perfect control, while with castings the moulder or founder can, at will or through methods in casting, give rise to an ill diffusion of the carbons that could often be prevented were he only aware of the conditions which effect such results in castings. The moulder when turning out a casting having hard or soft spots often finds the word '' segregation" very convenient to disguise evil effects of hard ramming, wet sands, or ill-vented moulds. When a mould has been properly made and the iron well mixed and melted hot and poured as it should be, there is generally little to fear, in a practical way, from segregation in castings that can be charged to the iron, aside from what effects degrees in cooling or casting in a chill can have in causing different proportions of combined or graphitic carbon A rammer should never be allowed to hit a pattern, as this causes a hard spot on the mould which, in light castings, can change the character of the carbons orhe one 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 "