PHYSICAL TESTS FOR THE BLAST-FURNACE, ETC. 507 By using together the chill-moulds of both sizes, as shown in Fig. 115, an excellent illustration will be afforded of the reasons why many castings crack or pull apart, owing to the work being badly propor- FIG, II?.—MOULD READY FOR CASTING. FTC 118.—FLASK AND PATTERN. tioned. The small pig test specimen will always show a greater contraction than the large one. Such ill results in cracks, etc., are often placed on the furnace-man1 s shoulders by claiming that he had sent''bad iron/' Should a furnace-man not care to use theseead to the one-sixty-fourth part of an inch, according as the space of contraction will permit the rule to be inserted between the chill-mould and the pig specimen, as shown. The lines being one-quarter of an inch apart, the scale can be easily read; but the rule could, of course, be graduated finer if desired.