CHEMICAL SCIENCE. 217 



tempering by dipping the hot metal in water in the usual manner, and 

 this, together with the color test, that is, the development of the series of 

 colors under different degrees of heat peculiar to steel, being taken as the 

 test of its formation. 



Let the kind of iron that is selected be the best, and, commercially, the 

 purest malleable iron, such as would be chosen for conversion into the best 

 steel. 



The manner in which the writer proceeded in these trials was as follows : 

 Little bars of this iron were made red hot in a porcelain tube, and then the 

 reagent washed over or sprinkled upon its clean surface, or the gaseous or 

 volatile matter (when such was used) was passed through the tube hold- 

 ing the red-hot bars. When the charcoal experiment was made, freshly 

 made and pulverized boxwood charcoal was selected, which was made red 

 hot to expel all adhering azotized or other gaseous matter; then quickly 

 transferred to the tube, the rod of iron imbedded in it, and the two ends of 

 the tube closed. "When, to this last arrangement, atmospheric air was 

 added, the ends of the tube, placed horizontally, were left open, and 

 the air, by diffusion, or by a quiet interfusion, found its way into and 

 within the body of the charcoal, and, of course, into contact with the 

 heated iron, 



It is needless to point out that this line of experimenting is calculated to 

 obtain, and aims at obtaining, only very broad indications of reactions and 

 effects ; for the iron used is only approximately and not absolutely pure. 

 But the indications of the special action of each reaction on its application 

 to the iron, are so marked and distinctive, and develop themselves so broadly 

 under the above system of testing, that this method of detecting the re- 

 actions, though not absolutely unqualified in its accuracy, is sufficiently 

 tangible for its intended purpose, and lies within reach of every one. It 

 will be seen how, in following up this investigation, for these comparatively 

 rude methods there are substituted others aiming at greater precision. The 

 temperature under which the following several reagents were applied to the 

 iron was that of a full red heat, or that usually employed in case-hardening, 

 or in the cementation process of conversion. Let any experimentalist pro- 

 ceed in this manner to apply to heated iron the following special reagents 

 and he will find : 



1. That heated iron exposed to the action of pure carbon, and kept out of 

 reach of contact with any other element, is not converted into steel. A 

 small rod of the malleable iron packed in boxwood charcoal in the closed 

 porcelain tube, and kept at a full red heat for twelve hours, did not, after 

 being tempered, show a hard steel surface ; nor did it exhibit the play, under 

 high and different degrees of heat, peculiar to real steel colors. It still 

 remained malleable iron. 



2. But that when atmospheric air is admitted to such an arrangement in 

 such quantity only as still to keep the carbon in excess, then, in the first 

 instance, the surface of the iron, and, finally (if the time of contact be long 

 enough), the whole of the iron, is converted into steel. 



3. That the application to the iron of gaseous nitrogen does not produce 

 steel. 



4. That neither does the application of carbonic oxide give steel. 



5. That the application to the iron of a hydro-carbon (as when olefiant gas 

 is passed through the tube, or when the red-hot rod is dipped into oil con- 

 taining no nitrogen) does not produce steel. 



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