364 J. Lawrence Smith on Emery. 
rR av hardness owing to the more or less Somapact: structure of the co- 
3 
ig 
ce a 
“rundum. 
By the method with the agate and glass:'I hae found the best 
emery capable of wearing away about one-half its weight of the 
glass (that used was the common Freneh window glass). The 
sapphire under the same circumstances :wearsaway more than 
four-fifths of its weight. A tabular view of ce will: be 
given a little farther on a Sa 
Chemical fenpbetetiie of Hiainy.° be Pe 
This substance consisting of a mixture of. corundum dnd oxyd 
of iron in various: proportions, it is easy tosee: what its composi- 
tion must be. “Yet the chemical examination of this mineral 
taken in connection with other properties is not devoid of interest. 
‘For the purpose of analysis, the emery was —— to a state 
of powder, in the manner alluded to in speaking of its hardness, — 
with a diamond mortar and sieve. This powder was dried for 
twenty-four hours over sulphuric acid ; a gramme was then weigh- 
‘ed in a small platinum crucible of about one-fourth of a cubic inch 
in Sapecitys fitted with é a cover that sagan itself well to it; this 
Thus arranged the crucibles were heated tg satanic for 
: r. After c g, thes pore: 
crucible was carefully withdrawn and weig bed “Th 
nished me with thé amount of water in the emery. °*" 
t requires a continued red heat to drive out all the Water, & 
circumstance which is true for a number of minerals, particularly 
or those containing a large amount of alumina as diaspore an 
the micas which will be spoken of in this 
wder, of which the water has been estimated, was next 
suilieniated to levigation in a large agate mortar placed on a sur- 
ace of glazed paper; and when completed, it was carefully de- 
tached from the mortar, placed in a platinum capsule, heated gently 
to drive off any hygrometric moisture and weighed ; the increase 
of weight furnished the amount of silica taken from the mortar. 
The levigation of one gramme was accomplished in two ope- 
rations, each requiring about twenty minutes; and by using @ 
mortar of convenient size and the extremity ‘of a feather or a 
small brush, it is possible to lose but an insensible quantity of the 
mineral and to with sufficient precision the amount of 
silica ot from the mortar. 
