If iron, when cast into a mold, is allowed to cool slowly, it is very liable to crystallize, and the crystals will so arrange themselves that the article which is manufactured will be likely to break off short when put to bear any great pressure. The remedy for this is "chilling,"whichis done by suddenly cooling the outer edge of the piece, or the part on , which the strain will come, and letting the rest cool gradually. If, however, the casting is large, this chilling, by the sudden contraction of such a mass often cracks the piece and renders it useless. Many proposals have been made to obviate this difficulty, but none are thoroughly successful. It is possible to make such castings as railroad car wheels and axle boxes with chilled surf aces,. and wherever they have been used, they have answered so well that they are now in almost general use.