MarcH, 1907. IRON METEORITES — FARRINGTON. 109 
nickel.* While few meteorites probably vary to this extent, such de- 
terminations. show the need of as thorough sampling as possible if a 
mass analysis is to be made. Occasionally a marked variation in 
the analyses of a meteorite seems explicable only on the assumption 
that the material analyzed did not belong to that meteorite. Such, 
for instance, seems the most reasonable explanation for the percentage 
of nickel, 12.67 per cent, reported by Hayes for Limestone Creek, as 
compared with the percentages, 25-30 per cent, obtained by other 
analysts. Errors of this sort are obviously difficult to detect, and can 
only be surmised in extreme cases. Another and more serious cause 
of discrepancies in analyses is the imperfect separation by the analyst 
of nickel and cobalt from the iron. The methods for this separation 
are not altogether satisfactory, even at the present day, and in earlier 
years they were much less so. Consequently the results of the 
earlier analysts were for the most part too low in these ingredients. 
The determinations of specific gravity shown in the tables appear in 
some cases to have been equally open to sources of error with the 
analyses. It can easily be calculated that the specific gravity of an 
iron meteorite is likely to be between 7.6 and 7.9, since the specific 
gravity of pure iron, 7.85, will be increased by that of nickel, 8.8, 
according to the proportion of the latter. It will be decreased by 
accessory minerals, such as troilite, which has a specific gravity of 4.7, 
schreibersite, 6.5, graphite, 2.2, and oxidized ingredients. Any poros- 
ity of the meteorite will also lessen its specific gravity. It is obvious, 
therefore, that determinations of specific gravity made on small frag- 
ments can hardly represent that of the mass as a whole, since they 
may contain a disproportionate quantity of accessory ingredients or 
may be more oxidized than the main mass. It is hardly credible that 
porosity or accessory ingredients of a meteorite would in any case 
reduce its specific gravity below 7. Determinations below this figure, 
therefore, probably indicate that oxidized material was used. From 
the showing in the tables that large numbers of meteorites have prac- 
tically similar composition, it is evident that similarity of composition 
cannot be used, as has often been done. hitherto, to prove identity of 
origin of meteorites found at different places. This method at one 
time obtained considerable vogue. Dissimilarity of composition, on 
the other hand, as a rule indicates separate falls. The only marked 
exception to this rule seems to be furnished by the two masses of 
Babb’s Mill, one of which shows about 11 per cent, the other about 
17 per cent, of nickel. The only alternative supposition possible here 
, * C. R., 1893, CXvi., 290. 
