176 Field Museum of Natural History — Geology, Vol. III. 



of the carefully sampled borings weighing 53^ grams was dissolved 

 in nitric acid. Although no residue was obtained, the solution was 

 evaporated to dryness, ignited so as to convert the iron to sesquioxide, 

 and an assay made by the crucible method. The charge used con- 

 sisted of 50 grams litharge, 25 grams soda, 25 grams borax glass, 5 

 grams scouring sand, and 4X grams argols. The lead button obtained 

 weighed 22 grams. On cupelling this no residue was obtained. 



A partial analysis was made of the crust of magnetic oxide de- 

 scribed on page 171. Fragments of this were broken off by careful 

 chiselling, and in this way .3396 grams were obtained. The material 

 was evidently somewhat hydrous and more or less coated with carbon- 

 ate of lime. It was dissolved by hydrochloric acid although acted on 

 very slowly by that solvent. Determinations of ferrous and ferric iron 

 in the solution gave: 



Fe O 20.84 



Fe 2 3 54- 60 



75-44 



The remainder which was not determined quantitatively, was chiefly 

 water, lime, C0 2 , and silica. The proportions of ferrous and ferric 

 oxide shown by the analysis leave little doubt that the mineral is 

 magnetite and show that the oxidation which the surface of an iron 

 meteorite undergoes in its passage through the air may produce this 

 mineral. 



COMPOSITION OF T^NITE. 



The composition of taenite, as is well known, varies between rather 

 wide limits. As these limits do not seem as yet to have been deter- 

 mined by comparison of analyses, the writer has endeavored to collect 

 all existing reliable analyses in order that such determination may be 

 made. The compilation of analyses together with a calculation of the 

 ratio of iron to nickel-cobalt-copper will be found below: 



Fe 



1 86.44 



2 85 .00 



3 85.00 



Ni 



13 .02 



14 00 



15.00 



Co 

 0.54 



83.28 .... 16 68 



80 . 30 19 . 60 



74.78 24.32 



73.10 23.63 



Cu 



04 



