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310                       MKTALLUKr.Y   OF   CAST   IRON.
a protection to the iron against oxidation, or being burned away while being-brought to a liquid state  that any disadvantage was apprehended. The author has no knowledge of the process by which the above member arrived at his conclusions, and can only say that to obtain definite proof of this claim steps differing from general practice in melting are necessary. The author, realizing this, made a series of original tests embodying sixteen heats, made in the twin shaft cupola Fig. 56, page 241, and shown in Tables 63 to 66. In making the comparative oxidation tests shown in these tables much care was necessary in preparing the cupola and collecting its refuse. In getting this cupola ready (Fig. 56) for a hent both departments were picked out and daubed up smoothly and then blacked over with graphitic or lead, blacking. Such a plan insured that no iron stuck to the sides from the preceding Cheats," to be melted down with, or change the irons obtained from the respective sides. The bottom was not dropped after heats, as in ordinary practice, but after the cupola had cooled down the* refuse was picked out from the top downward by hand, and every particle carefully pounded in a pan to discover any fine shot or pieces of scrap that might, exist in the burnt coke, dross, or slag remaining in the cupola at the close of a heat. This was then weighed on fine scales. By this plan not a single ounce of metal that remained as such could escape being found.
Heats Nos. i and 2, Table <\$, were charged with rolls that were cast from the same ladle, half being made in sand and half in chill molds, such as .seen at Fig. 59. The roll, castings were after the pattern seen in Fig, 58, which it may be said was the same form intiii*; will amount to u pound:;, which must be transformed into vapor at 500 derives F., involving 1.^,7.|o B. T, H. of beat, < )n the other hand, this amount is reduced by the heat expended in raising the average vapor of n.^, per cent, in <>; <lcj,rt***s air to Sou decrees I1*., which amounts to 2,714 B. T. I-,, leaving an extra. amount f r;,o;^> B, T. I*. coii:umed by the snow, which will aj;ain rcfpure about 3.ft pound;-; coke,