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502                      METALLURGY   OF   CAST   IRON.
fire clay, from three-fourths to one inch thick. It could, of course, be lined with fire-brick; the diameter of the shell being proportionately increased.
The baby-cupola shown is one which experimenters and college instructors could well use for giving in-structions in melting, and will be of value for scientific research in all cases where the melting of small iron will answer all practical purposes.
Horizontal chill-mould, and the specimen obtained therefrom for testing contraction or chill, is seen in Fig. 114, page 506. Two sizes of these pig-moulds can be used, or only one, as the furnaceman may deem best, in following out experiments and tests, as described later on. Fig. 115 shows cross-sections through the middle of the respective iron moulds; and the larger cross-sec-tion shows also the tapering-rule, D, applied at the end of the mould, to measure contraction. It will be noticed that the thickness of these miniature pig moulds or chills is one inch. Any variation from this thickness would affect the depth of the chill. It is, therefore, necessary that care should be exercised to have always the same thickness in any standard chill pig-mould which might be adopted, that did not exceed two inches thick. The author does not wish to be understood as advising records to be taken of the chill from the test-specimens, in cases where very fine results are desired, unless note be taken of the fluidity of the metal at the moment the chill specimens are poured. This is done in the author's system by means of fluidity strips attached to test bars, as at S, in Figs. 1.13 and 121, and also in Fig. 122, pages 503, 509 and 514.
In Fig. 121 a chill piece will be seen at B, which is the same as shown at A, Fig. 120, and which is a forma warm ladle to receive the liquid iron. The lining used for the cupola is simply a coating ofnovice desires to use the smallest cupola practical for melting small samples. "............      "        "   i in square hnrH........................