CHAPTER LXVI. PHYSICAL TESTS FOR Til 1C BLAST-PUR-XACK, AXD TIIKIk VALUE.* Progress in the science of either making or mixing iron requires a study of the physical as well as the ehemieal properties. The importance of a correct system for such tests, to make comparison possible between different furnaces, or the same furnace at different times, or with founders, is self-evident. The first, point to mention is the value of re-melting samples of the furnace-easts. The occasional re-melting of samples of easts, in a small cupola,, cannot, but aid the advancement <»f research, and serve as a chock on chemieul analyses, and often as a. protection to the fur-nareman, by enabling him to Irani what, the founder •/in do in ehanij'ing the character of iron after it has left the furnace yard. A little cupola will also often be convenient for easting small pieces for repairs that may be needed between the furnace-casts, or when a furnace is out of blast. A furnaeejnan is often n<»t informed of complaints eoiKvrning his iron until it has been all melted up; and then he has generally no remedy other than to inspect the eastings claimed to have been made from •* Kxtnirt u!' a n-viM'tl |>;i]»rr read at Am<TU'un Institute of Mining Kn^nu'rr:.' Mrrtiiu;, Prftsbur)', J'rb., iStjO. elements bringing about such close results.* The difference of 72 pounds between the two flasks poured on end, shown in Table 103, could be charged to the difference in the fluidity of the metal, which existed through lapse of time in pouring the two moulds, a quality affecting the strength, etc., of test bars more fully defined on pages 37.: and 5.»<>. Additional information on easting test bars on end will be found on pages 50,'*; anil 51.*.