on certain stony and metalline Substances , &c. 
*95 
same wa y* Fourthly, the weight of the magnesia is given, not 
immediately, as obtained by evaporation, but after a subsequent 
solution in an acid, and precipitation by potash. And, fifthly, 
the proportions are taken from the mean of two analyses. 
Nothing remains to be examined, of the stone from Benares, 
except the earthy matter, forming a cement or matrix for the 
substances already examined. 100 grains of this matter were, 
by mechanical means, separated as perfectly as possible, from 
the pyrites, iron, and globular bodies, and analysed as above. 
*1 he mean result of two analyses gave, 
- Silica _ 48 
Magnesia ~ „ „ - 18 
Oxide of iron - _ & 
Oxide of nickel - 0 r 
^ 2 
102 |-. 
EXAMINATION OF THE STONE FROM SIENNA. 
1 he external coating of this stone appeared to have the same 
characters as that of the stone from Benares. 
The pyrites, although certainly present, were not crystallized 
in such groups as in the preceding stone; nor could they be 
separated by mechanical means. 
The attractable metal was easily separated by the magnet ; 
but 8f grains only were collected. I treated them with nitric 
acid and ammonia, as in a preceding case. Nearly one grain of 
earthy matter was insoluble ; the weight was therefore reduced 
to rather less than 8 grains. The oxide of iron, precipitated by 
ammonia, weighed 8 grains ; and the saline liquor gave abun- 
dant indications of nickel. As 8 grains of this oxide of iron 
contain nearly 6 of metal, the quantity of nickel, in the bare 8 
Cc 2 
