44 MEMOIRS NATIONAL ACADEMY OF SCIENCES, VOL. XIII. 



Besides the two pieces of the Blake iron just mentioned, Cohen 28 had the Troost iron once 

 more investigated by J. Fahrenhorst, in order to be able to compare analyses by one hand and 

 by new and better methods. The results were as follows: 



100. 23 ' 100. 02 100. 68 100. 00 100. 00 100. 00 



1. Blake iron (Green County, 1876), from the end of the block with a large section surface. 

 2. Blake iron, from the end of the block with a small section surface. 

 3. Troost iron (Babbs Mill, 1842). 



4 to 6. The three analyses reckoned to 100, disregarding the sulphur, after abstraction of lawrencite (in the 

 Blake iron) and echreibersite (in the Troost iron). 



The analysis of the Troost iron thus corresponds very well with the two former analyses 

 by Clark and Cohen. That this is not the case with that of the Blake iron specimens may be 

 due to the fact that in the first, by Cohen and Weinschenk, less trustworthy methods of sepa- 

 ration were employed. 



The difference between the chemical composition of the Troost iron and Blake iron 

 specimens is, according to the above results, so noticeable as to occasion doubt whether both 

 masses really belong to the same fall or not. On the other hand, it seems hardly probable that 

 so unusual a phenomenon as the occurrence of ataxites rich in nickel should have happened 

 twice in a narrowly bounded space, and, moreover, two ataxites which are structurally abso- 

 lutely alike. Also, in respect to chemical composition, a noteworthy chromium content is in 

 both masses combined with the total or almost complete absence of sulphur, a phenomenon 

 which has hitherto been noted only in the Cape iron. Cohen 29 inclines to the supposition, 

 therefore, that both masses belong to the same fall. 



The mass of 1876, or Blake iron, is chiefly preserved in the Vienna Museum; the Troost 

 iron is more or less distributed. 



BIBLIOGRAPHY. 



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