IMPRACTICABILITY OF HARDNESS TESTS FOR PIG IRON. 179
obtain that which, is best to exist in their castings as nearly as possible. When this day arrives we will hear no more of being" guided by the appearance of fractures or hardness, unless, by better regulation of furnace workings and the casting of metal from ladles into iron chill moulds may, in years to come, cause the appearance and hardness of fractures to agree with the chemical analysis; but this is doubtful of achievement to the perfection that should be obtained.
In the " Foundry " of November, 1901, a statement is made,
tinder the head of " Cast Iron Notes," inferring that two furnace casts of gray pig iron of the same analyses and brand, but of different grain or fracture^would give a different grade or character of iron in like castings. This is practically the same as thinking to correctly judge pig iron by its hardness, as, in either case, the hard or close grained pig has more combined carbon than the soft or open grained pig and as a fact, the samples Nos. i and 2, Fig- 43, are of like analyses, excepting the graphitic and combined carbon, but, if remelted under like conditions, as could be done in the cupola shown on page 241, castings of like softness would be produced; at least, so close that there would require to be a much more radical difference in the grain of two furnace casts, of like analyses in the same brand, than is shown by the samples Nos. I and 2, Fig. 43. The difference that a very open and very close grained iron of the same analyses and brand could make would be in the most close grained iron giving a slightly softer casting than the open iron, after the principles presented in Chapter 47, pages 337 to 339. However, there is no reason why any one should make it a point to insist on accepting only open or close grained iron in connection with exacting any certain specified analyses from blast furnaces, as the slight difference possible in the most radical cases of open and close grained iron can be regulated by a slight variation in silicon when making a mixture, and which anyone can easily do, if they so desire, "