1831,] 
Chemical Analyses. 
279 
sure of the angles, and under the microscope the facets of the laminae appear 
rounded and uneven. The laminae can be split with facility, and are somewhat 
tough and unelastic : their lustre is bright grey metallic, resembling specular or 
micaceous iron ore, and they soil paper with the usual streak ofhlacklead. 
The mineral is found apparently in small lumps of an inch or two in diameter; 
and judging from the impurities adhering to the surface of the nodules, the 
gangue, or parent rock was probably gneiss : the fibres seemed in some specimens 
to be cut off by a transverse vein of quartz. 
The specific gravity of a fragment, first deprived of as much air as could be 
separated by immersion under water in vacuo, was found to be 2.37. 
100 grains heated under the muffle of an assay furnace, required several hours 
for their incineration ; and when they appeared to be reduced to an ochreous ash, 
solution in nitroinuriatic acid proved that a number of the scales had still escaped 
the action of the fire : before the blowpipe, the substance was equally refractory. 
The loss of weight, after complete incineration, was 62.8 grs. The oxyde of 
iron was separated from the ash by means of nitromuriatic acid, and the earthy re- 
sidue analysed by fusion with potash in the usual method : the composition 
thence deduced was as follows : 
Carbon, 62.8 
T c r Carburet of iron ? 68 
Iron, 5.4 ^ 
Silex, 21.0 
Alumine, 9.3 / 
Lime, 0.2 > Earthy impurity 32 
Magnesia, 0.1 W 
Manganese, a trace, and loss, . . 1.2 j 
100 100 
Suspecting from the large proportion of earthy impurity in this analysis, that 
some of the matrix had remained mechanically mixed with the graphite, I select- 
ed some of the fibrous crystals with care, and submitted them again to the fire : 
Hie results proved that it was the case : 
h The graphite uncleancd left, as above, iron and earth, per cent 37.2 
2- Roughly cleaned, left a residue per cent 18.5 
3- Crystals selected with care, 6.0 
4- Another trial left the very small proportion of 1.2 
fi'o two last residua did not entirely dissolve in muriatic acid, indeed the for- 
nier yielded 0.3 of silex on analysis ; it is difficult therefore to assign a definite 
composition to graphite, and almost justifiable to suppose that the presence of 
lron itself is not indispensable therein. In chemical works, the amount of iron in 
the carburet is made to vary from 5 to 10 per cent, but I find in the last edition of 
fire’s Dictionary, that “ the researches of Karsten have proved beyond a doubt, that 
graphite is merely a peculiar form of carbon in proof of which the graphite of 
finrreros in Brasil is said to leave hardly any ash when burned. 
In the present instance it is clear that the earthy impurities are merely acci- 
denjal, and, as might naturally be expected from its crystalline form, the mineral 
kself is quite pure. The ore however would require careful dressing before it 
could be converted to any useful purpose in the arts, and it differs essentially from 
quality of plumbago preferred for making pencils, which is described as a 
compact close-grained sectile graphite of great purity. Having been favored with 
a figment of the Borrowdale mineral, from an English cabinet, I was anxious to 
Iu< dte a comparative examination of it ; but I was checked at the outset by the cor- 
