380 Plumbago in Coal-Gas Retorts, Se. 
13. Plumbago in coal-gas Retorts.—The following de- 
scription of an artificial plumbago, is by the Rev. J. J. Co- 
nybeare ; he is speaking of the retorts in the Bath. gas- 
works. The unserviceable retorts, on being withdrawn 
from their beds, are found lined with a coating of plumba- 
g0 averaging the thickness of four inches. . This coating is 
thickest towards the bottom of the retort. The yeneral 
aspect of the predominant variety may be thus described : 
colour, iron-grey, somewhat lighter than that of native plum- 
bago ; texture ataly-s ; structure mammeillated, usually in ve- 
ry. close a aggregation—some specimens exhibit this structure 
on the large scale, but, generally it requires the lens, to. be 
seen ; hardness variable, but. always greater than the 
native plumbago—scratches gypsum, but is scratched, by 
calc. spar; dusire of the fracture sieaiie but small ; lustre of 
the exterior. surface sometimes very considerable, ; the 
ewder uniformly resembles that of common plumbago, 
t is somewhat less brilliant. The quantity of iron in. it 
seldom appeared to amount to 9 percent. It is hardly fit 
for the finer purposes of art, but it is proposed to use it in 
diminishing friction, in ibn sencibler furnaces, &c. 
Phil. Ve, Rs * 
rs Analysis oe Uemvacaih pa has lately reanaly- 
zed this mineral and very unexpectedly finds it to contain 
phosphoric acid ; a to bea net < A ApCGmRCE 
from Cornwall gav: 
Silicia . gan ‘ mete aad 
oe hosphoric.acid,, 5.02... =. 4.49 «+..1600 
, Oxide of Uranium, - ... -). - _,,60« 
_. Oxide of Conpet, hestvaselttsecetn td Pacael ae 
ater,....:; + Soult deek chert 
: tT 100. ° 
re emp the Silicia, , 
: eee hate of cone Be aneed ori S 
te . - hs =. -. eee 
wre thE PRR oi 
: - 14.5 
Ann. Phil. v. 59- 
