CHAPTER LVI. UTILITY OF CHILL TESTS AND METHODS FOR TESTING HARDNESS. In regard to the general utility of chill tests, some have believed that if a founder knew what an iron would " chill " in some test bars or block chills, he should be able to define what depth of chill any casting- would have, 110 other qualities being' known than that of the iron used and form of the easting-. There are numerous elements which affect the depth of chill in a casting;, other than the chilling- qualities of the iron used, which make it impracticable to say just what the depth of chill in a casting- will be, from the depth of chill in a test bar or block. All we can do with a test bar or chill block is to g'ct a relative knowledge, of the natural chilling' qualities of an iron. To illustrate this, I will state a few principles: First. Any casting- will show a deeper chilling' by remaining1 in contact with its chill until all the metal in the casting" has solidified or it becomes cold, than if the union of the casting- or chill were broken before it. had occurred. Second. A hot-poured iron will remain longvr in contact with a chill than a dull-poured iron, for as soon as the molten metal has solidified i! commences to contract, and hence it must be plain to any one that the same grade of iron, if pulled away morem. This founder's achievement involves a lesson not to be forgotten by any interested in the founding or designing of machinery.