4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 10 



nickel content differed. The following quotation from J. S. March, 

 "Alloys of Iron and Nickel," p. 512, seems worthy of repeating: 



In 1916 Stead ^ reported that the scales of nickel steels consist of several 

 layers and that the nickel content of the layers differed widely. For example 

 the outermost layer of scale on a 25% nickel steel consisted mainly of iron 

 oxide, whereas the innermost layer included particles of metal containing 76% 

 nickel. These findings were amply verified by Pfiel ^ who found the scale on 

 iron and steel to consist of three layers, on a 2.75% nickel steel the outermost 

 layer of scales contained no nickel, the middle layer 0.16% and the innermost 

 layer 7.07%. 



March further states (p. 511) : 



Once a continuous film is formed further oxidation must proceed by dif- 

 fusion of oxygen through the oxide layer. Cracking and peeling of films in 

 service are often to be ascribed to bending or cycles of heating and cooling. 

 But the absence of such stresses, cracking may result when the metal surface 

 is converted to oxide, volume changes leave the film in a state of compression, 

 and it can be shown that these stresses result in cracking when the thickness 

 of the film exceeds a limiting value. 



This explanation seems to account for the structure shown by the 

 scales in this cavity. 



The surface appearance of these scales resembles that of the bottom 

 of the meteorite. Any water falling on the exposed surface would 

 drain off easily, and that accumulating in the upturned depression 

 would rather rapidly evaporate. Moisture evaporating from the 

 ground would condense and be retained on the under surface of the 

 specimen or in an inverted depression; hence these parts have been 

 exposed to many more hours of hydrous alteration. Some of these 

 deep holes did not show any excessive accumulation of iron oxide. 

 There is one cavity in the large piece removed for sectioning which 

 extended through three of the slices. The iron oxide that had formed 

 around the surface of this hole was not of equal thickness all around 

 the cavity. This oxide also cuts across the internal pattern of the 

 meteorite. 



The 22-pound specimen removed for sectioning was found to con- 

 tain few small troilite inclusions ; hence we do not attribute these deep 

 holes to the burning out or weathering out of troilite. The depth of 

 these depressions suggests that they may have been in existence prior 

 to the time the meteorite entered our atmosphere. 



A sample of scaly material was analyzed. Several other pieces of 

 scale were polished and found to contain small inclusions of metallic 

 iron. 



1 J. E. Stead, Journ. Iron and Steel Inst., vol. 94, pp. 243-248, 1916. 

 - L. B. Pfiel, Journ. Iron and Steel Inst., vol. 119, pp. 501-560, 1929. 



