I42 METALLURGY OF CAST IRON.
mixed, pig about, in the same pile of ten hundred to a ton each, so that when charging time comes there are no distinct iron piles of high and low silicon to make a mixture of, which must be carefully guarded in order that no more of one than another, as desired, goes into the cupola; but it allows any pile to be used, and if the'men are careless and make blunders they can do no harm, as with the former plan. This latter method involves no more labor in piling the iron on a cupola stage than the former and is superior in giving a uniform mixture, if stage room will permit of such a practice.
The gradual introduction of satidless pig, cast from ladles, is a step which will greatly help in giving the founder uniform casts of pig iron, as first catching the metal in large ladles before pouring the pig moulds cannot but act as a mixer and cause the one ladle or cast of pigs to be more uniform in their chemical composition than is^ possible by casting them in sand moulds, after the old method. By this plan each ladle's cast of pig could be analyzed. This would give positive assurance of obtaining certain'bodies of iron that would be uniform in analysis, without having to resort to mixing each cast of iron. These are all factors which strongly recommend the use of sandless pig iron. For methods of calculating percentages of silicon, sulphur, etc., as found in iron, to obtain averages for making mixtures, see Chapter XXXVI.
Another evil practice, aside from ill-mixing of sand cast pig iron, is the practice which some furnacemen making foundry iron have followed of only taking one analysis of one of the four to five casts a furnace may make during twenty-four hours, and letting thee above plan, they areter 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 "