MECHANICS AND USEFUL AKTS. 77 



of pig iron. The crude iron from which wrought iron of the best quality is 

 produced, is that possessing a medium degree of rarburatiou, usually termed 

 grey pig iron, while iron which possesses an inferior degree of fluidity, is 

 what is generally used for the manufacture of wrought iron, especially when 

 the conversion is effected by the single operation of boiling in the puddling 

 furnace ; but it is always more impure than grey, and does not produce the 

 best wrought iron. In those countries where the pig iron is smelted with 

 charcoal, and where coal is available for conversion into malleable iron, the char- 

 coal refinery is generally abandoned for the puddling furnace, it being found 

 that the quality of the iron is sufficiently insured by its previous treatment. 

 In Great Britain, where the smelting process is almost exclusively conducted 

 with coal or coke, nearly the same result is obtained with reference to the 

 quality of the bar iron produced by the treatment of .the pig iron in the char- 

 coal refinery with charcoal; it therefore becomes an important subject for 

 investigation, to ascertain what are the precise causes to which this ameliora- 

 tion of quality from the use of vegetable fuel is due, when used in the treat- 

 ment of iron in processes which have no analogy to each other. He considers 

 that the circumstances of the two cases point to the possibility, that the 

 eliminated effect exercised as fluxes in both instances by the ashes of the 

 vegetable fuel employed, may have some influence in producing this improve- 

 ment in quality, and that, should such be the case, we may replace charcoal 

 as fuel with advantage by artificial fluxes producing an equivalent effect. 

 The charcoal refinery in general use in those countries where mineral fuel 

 is not accessible for the conversion of crude into malleable iron, is still" 

 extensively employed in Great Britain, when it is desirable to produce iron 

 of the best quality. Mr. Blackwell points out that grey pig iron smelted 

 with coke may be converted into malleable iron by the boiling process, there- 

 by avoiding the serious waste from oxidation in the coke refinery, and it 

 becomes important to inquire whether any ameliorations can be introduced 

 which would enable it to be more universally adopted than it hitherto has 

 been. He remarked, however, in general terms, that the principal mechanical 

 agents hi these operations are the hammer and the rolls, and that it is by a 

 proper combination of both that all the requisite qualities of weh 1 manu- 

 factured iron can be obtained. He observed that in England latterly, there 

 had been a tendency to supersede the use of the hammer by that of the rolls, 

 not only in small sizes, where the immense command of power rendered it 

 practicable to do so, but in larger sizes also as, for instance, rails, large bars, 

 plates, and thick sheet iron, where it was not practicable, if soundness was 

 to be secured. 



TEST OF STEEL 3IANUFACTUKES. 



A correspondent of the Journal of the Society of Arts (London) publishes 

 the following method of testing the quality of steel by means of nitric acid. " I 

 first carefully clean the articles from ah 1 grease with a little turpentine, as 

 grease resists the action of acid on metals, and then immerse about two 

 inches of their length in acid, which should be slightly warmed, as it ' bites ' 

 better when tepid. If the acid be too strong, its biting will be rather slow. 



