C 398 3 
XV. On the Composition of Emery. By Smithson Tennant* 
Esq . F. R. S. 
Read July 1, 1802. 
The substance called emery, which, from its great hardness, 
has been long used in various manufactures, for grinding and 
polishing other bodies, has not, it appears, been hitherto cor- 
rectly analyzed. In books of mineralogy, it is considered as an 
ore of iron ; an opinion probably derived from its great specific 
gravity, as well as from the iron which it frequently contains. 
But, where this metal is most abundant, it could not be extracted 
from it with advantage, and ought rather to be regarded as an 
impurity, as it does not contribute to produce the peculiar hard- 
ness for which this substance is distinguished. In Mr. Kirwan's 
mineralogy, he mentions an examination of emery made by 
Mr. Wiegleb, from which he inferred that 100 parts consisted 
of 95>6 of silex, and 4,4 of iron. Mr. Kirwan, however, justly 
suspects the correctness of this account, and observes that he 
had no doubt but some other stone was imposed upon Mr. 
Wiegleb for emery. 
When powder of emery is boiled in acids, it becomes of a 
lighter colour, from the loss of part of the iron ; after which, it 
does not seem to undergo any further alteration. As acids produce 
so little effect on it, I exposed it to a pretty strong red heat, 
with carbonate of soda, in a crucible of platina. On adding 
water to the mass contained in the crucible, the greater part of 
