Mr. Tennant on the Composition of Emery. 399 
the emery was found in powder ; having only become of a light 
colour, from the extraction of part of the iron. Though this 
process was twice repeated with the remaining powder, and in 
a stronger heat, a great proportion of it remained undissolved. 
The alkaline solution,- after a red calx of iron had subsided 
from it, was .saturated with acid ; and gave a precipitate of a 
white earth, which 1 found to be almost purely argillaceous. 
The result of these experiments, was so similar to those of 
Mr. Klaproth on diamond spar, as to render it very probable 
that emery was in reality the same substance, though usually 
mixed with a larger proportion of iron ; and the subsequent ex- 
periments appear to confirm this opinion. 
In order to obtain a quantity of emery as free from iron as I 
could, I reduced to a coarse powder, a piece which consisted of 
different strata, some of which were of much lighter colour 
than others ; and afterwards separated, by a magnet, the par- 
ticles which were attracted by it. The part which was not 
attracted by the magnet, I observed to have the usual degree of 
hardness, (by the scratches which might be made with it on 
flint.) I then reduced it to a finer powder, in an agate mortar; 
and, as this was principally done by pressure, and not by 
grinding, hardly any sensible addition was made to its weight. 
In the same manner, I found that diamond spar might be 
powdered to the same degree of fineness, without any material 
increase of weight from the mortar. 
Of the emery powder thus prepared, 20 grains were taken, 
and heated in the manner before described, with 120 grains of 
soda, which had been previously deprived of carbonic acid, and 
boiled to dryness in a silver pan. By nearly the same process 
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