90 J. L. Smith on the Emery mine of Chester, Mass. 
less appropriates a portion of the alumina, thus reducing the 
alumina attributable to corundum; so that, were it possible to 
So again, if we compare Nos. 8 and 1, the ibotte hardness will 
be found in the proportion of 42 to ‘87, while their amounts of 
alumina vary only as 60 to 63; but if we regard the amount of 
water in the two it is as 5°6 to 1° 9, much of this water comin 
from diaspore that is intimately mixed with the corundum ; an 
in several specimens I possess, the two minerals shade into each 
other so completely, that it is impossible to tell where one be- 
gins and the other ends. The above facts were all well examined 
when my first memoirs appeared on this subject, which accounts 
for the following remark then ma 
“Those emeries which contain the least water, everything 
else alike, are the hardest, as instanced by that from Kulah, not- 
withstanding the quantity of iron it contains. The silica exist- 
ing in emery is most often in combination with alumina, or the 
oxyd of iron, or both; for this reason we must not always re- 
gard the quantity of alumina as an indication of the quantity of 
corundum in eme 
In concluding this part of the subject I would state that while 
T do not consider my opinions infallible in this matter, still all 
my experience and research, gathered from suc varied sources, 
point to the conclusion that emery is a mixture of —_ min- 
erals, principally corundum and magnetic oxyd of iron, 
former being the effective agent in the mechanical “thane to 
which it is applied; the o oxyd of iron is not to be considered as 
an unimportant ingredient, it serving by its presence to eee: 
to some extent the harsh cutting aioe of the corundum 
Minerals associated with the emery of Chester. 
Corundum.—This mineral, as might naturally be expected, is 
found with the emery, seem distinct and separate to be at 
once recognized, sometimes in t seams, massive in its charac- 
ter, but more commonly in a fastened crystals of small dimensions. 
Diaspore.— ery excellent and beautiful specimens of be 
hydrate of alumina have been found at this emery locality; 1 
is often in distinct and separate prismatic or bladed crystals, 
quite — and transparent. 
EB te or Margarite.—Some of the finest s ens of this 
mineral that are known have been fognd at this "ooality, ‘ 
