CHAPTER XXXVII. CONSTRUCTION OF CHEMICAL FORMULAS AND EFFECT OF PHYSICAL ELEMENTS IN CASTING CHILLED WORK. Chemistry has proved of greater benefit in making mixtures for chilled castings than in any other line. When the progressive founder thinks back to the days when the chill roll, car wheel, and other manufacturers were guided wholly by judgment of fracture in selecting their pig metal to make a mixture, he is not at a loss to comprehend why such bad results in castings were then obtained, accompanied by heavy financial losses. In making grey iron castings, there is a much greater margin for a divergency from the best point to be reached as regards the 'i grade '' desired than with chilled work. 'In many cases where soft work is wanted it ma}T be found very hard and still be passed, or do no injury other than cause extra labor in finishing the castings, etc.; but as a general thing if chilled mixtures diverge much from the best point to be attained, the castings will prove worthless by reason of " chill cracks " or the " chill " not be of the depth or quality of hardness desired. It is true that most chilled work founders would take "chill tests " of their mixture after they had melted their irons. Thisesented, there are cases where one may utilize different percentages of silicon, sulphur, etc., by mere mental calculation, after the ideas seen on page 141, that may answer all practical purposes. While the rules of Tables 39 to 42 may appear, at first, complicated, to those unaccustomed to such computations, they would, with a little practice, soon find the methods very simple.ABLE 39.