THE METALIiOGRlAiPHY OF METEORIC IROilSr 77 



ing view among astronomers that all meteors belong to that system. 

 Von Nissel, however, and more recently Hoffmeister (1937) offer 

 quite convincing evidence that many meteors have hyperbolic 

 velocities and therefore come from without the solar system. If 

 this view be accepted, a meteor with a hyperbolic orbit might con- 

 ceivably have been reheated to any degree by a close approach to 

 the sun or a hot star, cooling again as it receded. It is also possible 

 that a meteor with an elliptical orbit might pass close enough to the 

 sun to be heated sufficiently to produce structural changes if the 

 effect were intensified by countless repetitions of such an approach. 

 As the conditions of production of meteors are wholly conjectural, 

 any imaginable combination of time, temperature, and pressure 

 may be considered theoretically possible. The author, however, 

 is inclined to minimize the importance of such possibilities, because 

 they could account for only exceptional structures; v/hereas the 

 structures of meteoric irons are remarkable for their substantial 

 uniformity within any given range of composition. 



XIV. THE ROLE OF PHOSPHORUS IN METEORIC IRON 



Of the nonmetallic elements in meteoric iron only three have 

 appreciable influences upon its structure — phosphorus, sulphur, 

 and carbon. Of these phosphorus is the most important. Its influ- 

 ence was early surmised and later demonstrated by metallographic 

 studies. Vogel has treated this subject exhaustively in a series of 

 contributions embodying the conclusions reached from heat treat- 

 ment of meteoric irons and artificial nickel-iron alloys, the use of 

 picrate etching (then recently developed), and interpretations of 

 the ternary iron-nickel-phosphorus diagram. Some of his more 

 important conclusions will later be referred to. 



Schrcibersite.— Phosphorus in artificial irons exists only as phos- 

 phide (FcgP), and in meteoric irons as the nickel-iron phosphide 

 schrcibersite — (Fe-Ni)3P; or since it may often contain cobalt, 

 (Fe-Ni-Co)3P. As explained in Chapter IV, schrcibersite varies 

 in its phosphorus content, some analysts reporting ratios of Fe-Ni 

 to phosphorus as greater than 3 to 1. Such variations may perhaps 

 be explained on the assumption that the material analyzed was not 

 pure phosphide but an Fe-FcsP eutectic (p. 79). 



Schrcibersite usually is clear with ordinary etching, but is blackened 

 by neutral sodium picrate. When a eutectic structure is present it 

 may be visible with ordinary etching (pi. 59) though sometimes not 

 (pi. 61). Kamacite with a low phosphorus content (below 1.7 per- 

 cent) may be slightly darkened (pi. 57). 



Picrate etching often produces a reticulated pattern on phosphide 

 areas (pis. 55, 56, 57). This, however, does not indicate such a 



