THE METALLOGRlAPHY OF METEO'RIC lElON 71 



plessite. Rinne and Boeke (1907) carried similar investigations 

 further, finding that the taenite in fine plessite fields became diffused 

 by heating, and that the fields took on the appearance of the altered 

 kamacite m the bands. From this fact the important conclusion 

 was drawn that the structure of such plessite is not one of primary 

 crystallization from the melt but a transformation product formed 

 during the cooling of the solid solution. In more recent years this 

 field of study has been thoroughly explored, notably by Kase (1925) 

 and by Vogel (1927, 1932), who made exhaustive researches involving 

 the heat treatment of meteoric hons and related artificial alloys. 



Artificial heating. — As to nickel-poor ataxites being a product of 

 artificial heating, there are a few cases where that explanation might 

 possibly be entertained. Of the six regarded by Berwerth as arti- 

 ficial metabolites, tlu-ee have no definite history of such heating. In 

 the other three cases that conclusion might be sustained in the case 

 of Hammond because it was heated in a forge and a piece cut off. 

 One of the Babb's Mill irons (the Troost iron) also was heated to 

 determine whether it contained silver. 



Such heatings may have been high enough and long enough to 

 produce structural changes, although that seems improbable. In 

 the case of Rafriiti, which for some years had been heated by a farmer 

 in winter for domestic purposes, it does not seem possible that any 

 change could have been produced. Though according to Tammann 

 granulation begins to appear after prolonged laboratory heating at 

 as low a point as 400°, any ordinary heating sufficient to produce 

 even incipient granulation in kamacite could hardly be less than 

 550° continued for many hours (Kase, 1925), which would corre- 

 spond with a blood-red heat. Before sclu-eibersite would begin to 

 melt the temperature would have to be about 1,000°, which would 

 produce a very bright (orange or lemon) red. 



The failure of a rather strong artificial heating to produce struc- 

 tural changes is illustrated in the case of the Cedartown hexahedrite. 

 The house in which it was kept was completely destroyed by fire 

 and the meteorite later recovered from the ashes. Though it pre- 

 sumably may have been heated for a time to a dull red heat, the 

 microstructure shows no trace of alteration. No new granulation 

 appears, schreibersite needles show no diffusion, and even Neumann 

 lines remain perfect. 



We may fairly conclude that artificial metabolites, though perhaps 

 sometimes produced, are rare. 



Natural reheating. — As to alterations of structure by natural re- 

 heating, there is no uncertainty. The evidences of it are conclusive, 

 and the same effects have been produced experimentally under 

 controlled conditions. 



