216 ANNUAL OF SCIENTIFIC DISCOVERY. 



tion of the surface. Finally, as the ne plus ultra of his testings, he will pro- 

 ceed, probably, to forge out of his specimen a turning-tool, or preferably a 

 cold-chisel, and then with the latter, cutting for awhile at a piece of cold 

 cast-iron, will at once pronounce upon the kind and the quality of the metal, 

 and the exact purposes to which it is best applicable. Now, from the nature 

 of the case, the chemist must imitate or select from these practices of the 

 handicraftsmen (for there exists no special test); and the file test, after 

 tempering, together with the color test under high and different tempera- 

 tures, affords sufficiently accurate tests for most of the purposes of the labo- 

 ratory. 



The searcher for information among the steel-makers and steel- workers 

 "Vill speedily find abundance of instructive and suggestive facts, the careful 

 study of any one of which may possibly give him the clue he seeks for. 

 Let him, for example, in the first instance, carefully examine the phenomena 

 Involved in the very old practice of using ferrocyanide of potassium as an 

 agent of conversion. It is well known that the application of this compound 

 to heated iron instantaneously converts that portion of the metal that is 

 brought into actual contact with it into steel; and that under a continued 

 contact, the entire mass, as well as merely the surface of any piece of iron, 

 equally undergoes this transmutation. Thus, this agent is used to improve 

 'ftie quality of inferior steel, that is, more completely to effect the conversion 

 of iron into steel ; is also sometimes resorted to to renew or to restore the 

 steel quality of steel tools for example, of chisels, the repeated heatings 

 and forgings of which have decomposed the steel externally, or to a greater 

 or less depth reconverted it into common iron It is used more especially to 

 ^ase-harden iron; that is, to give to iron an external coating of steel, or to 

 improve soft steel by its more complete or perfect conversion superficially. 

 This ferrocyanide of potassium is a carbon compound, containing, in its 

 anhydrous form, no oxygen; and, doubtless, it would be on some theory of 

 its carbon-giving agency, that its application (could we possibly trace the 

 origin of it) to iron was first made. But, besides carbon, it contains also 

 xron, nitrogen, and potassium. Its formula is, KL>, Fe Cys (or 3 NC2). 



Now, the specific action of this reagent, or the cause of its producing this 

 singular effect the instantaneous conversion, at the points of contact, of 

 iron into steel might, a priori, be held to be due to one or other of the fol- 

 lowing kinds of reactions. 



1. To the reduction of some portion of the carbon of the reagent, and its 

 being taken up by the hot metal with the usual result of such a combination, 

 as viewed on the old theory of what steel is. 



2. To a deposition upon the surface of the hot metal of a thin film of the 

 pure iron, combined in some peculiar proportion or manner with the pure 

 carbon, both of which exist in this reagent itself. 



3. To some peculiar action of the potassium present in the reaction; or, 



4. To some peculiar action of the nitrogen of the reagent, or of that ele- 

 lient and its associated carbon existing there in the form of cyanogen. 



For merely preliminary trials or indications, let there be selected some 

 ready method of determining which of these elements, or combination of 

 the7n, plays this part of conversion; and for this purpose, let there be taken 

 as the test the formation or the nonformation upon the surface of soft iron 

 of a case-hardened surface, or of a superficial coating of steel as the result 

 of an application to the iron of one or other of the following reagents ; the 

 relative hardness of the surface being determined by the file test ; and after 



