360 Mr. Mallet on the Physical Conditions 



best result for castings of one dimension cannot be true or applicable to castings of any 

 greater or less scanllin2. 



Thus, if, as Mr. Fairbairn concludes, the thirteenth melting gives the best metal, for trial 

 bars cast one Incli square, with tlie original "make" of pig-iron, and mode of melting and 

 casting, he employed, — it does not follow that for bars of two inches square it would be so ; or 

 that, with the one-inch bars, but a different original " make" of pig-iron, or a different cupola, 

 it would be so; or even with the same pig-iron and conditions of melting, but a different 

 mode of moulding and casting the same one-inch square bars, the result should be alike. If, 

 with the very same pig-iron, cupola, and fuel, the meltings be performed with a surcharge 

 of metal and flux in proportion to fuel, and an excess of blast, the one-inch square bars, when 

 cast, would have been found to have arrived at their assumed best quality, perhaps, at the 

 fourth, in place of the thirteenth, melting. If the bars themselves had been cast in " chills," 

 in place of sand-moulds, so as to have been cooled as fast as possible, the point would have 

 been still sooner reached, and, if cast in " dry sand-moulds," or "in loam," would have been 

 later reached. 



Upon sample bars so small as one inch square, even a little more or less wetting of the sand of 

 the greensand-mould, on the part of the moulder, would have made the most formidable dif- 

 ference as to the rate of progress towards white iron. Finally, if, instead of bars of an inch 

 square, the experiments had been made upon a sufficient scale to admit of casting bars of a 

 foot square, these, when broken after the thirteenth melting, in place of presenting the same 

 assumed improvement, would in the interior have presented very little change in fracture 

 from the original pig-iron (unless, indeed, peculiar care had been taken to so work the 

 cupola as to burn out in it the graphites — a thing most difficult to accomplish at all upon 

 a large scale, and not in question here) ; and in place of the thirteenth melting being the 

 charmed one, it might not be reached at the 13 x loth melting. 



The conclusion drawn by Mr. Fairbairn is, therefore, too large, is not warranted by a 

 just interpretation of the premises, and might lead to serious mistakes in practice; for, 

 as has been shown in the text, this same best quality of iron, this same combination of 

 strength and toughness, can be obtained direct from the ore in the blastfurnace, and either run 

 into pigs, or, far belter, cast into guns or other large objects requiring it, at once, and without 

 any intermediate cooling. The whole roundabout process of repeated melting is, therefore, 

 perfectly needless — but, further, it is positively hurtful ; for, every time cast-iron is melted 

 in contact with fuel and flux, it takes up a fresh additional dose of the metallic bases of the 

 alkalies and earths; and it is to the alloy of these, especially of the latter, that a more fatal 

 reduction of strength and toughness is due, than to any other foreign mixture with which 

 cast-iron is known to combine — so that, by this notion of repeated meltings, we spoil the 

 pig-iron in trying to effect, by an indirect process, what, with better knowledge, should be 

 the direct result of the primary and single operation of the smelting furnace. 



