- 
#34 Experiments made at the Polytechnic School 
tefift the action of pot- -ath by the humid way: 100 party 
put in digeftion in that folvent, left im it 4°6 of alumine. 
The fecond was, to afcertain whether this combuftible; 
which poffeffed fo little inflammability, had alfo the power 
to alcalife more nitre than carbon, confequently to take up 
more oxysen. Three fucceffive trials gave for a mean refult 
the alcalifation of 7°87 parts of nitre by one part of that mi- 
neral; and the fame coally matter, digefted for four or five 
days in oxygenated muriatic acid, burnt completely with 6°5 
of nitre. 
M. Klaproth, the celebrated chemift of Berlin, had brefots 
fubmitted to trials of the fame Kind a foffil deferibed by M. 
Widenmanin under tht name of incombuftible coal, and found 
that 100 parts left, after combuftion at a very flrong heat, 
only feven of a cineritious refiduum ; that treated in a cru 
cible with eight parts of nitre, and the mafs diffolved in water, 
acids occafioned no precipitate. Kirwan, in his experiments 
on coal, remarks, that that which he calls Kilkenny coal, and 
which has a metallic brilliancy, which does not burn but 
when carried to incandefcence, and which then comfumes 
flowly without emitting flame, can decompofe 9°6 of nitre. 
After this I do. not fee how there can remain any doubt’ 
that thefe fuppofed incombuftible fubftances are real oxydes 
of carbon, which, like coal or charcoal, have the property of 
conduéting the electric fluid; of cementing iron; of taking 
the oxygen from fome acidifiable bafes; but which are not 
at that degree of oxydation neceffary for exerciling this fepa- 
rating affinity at a weak temperature. 
I muft not omit this opportunity of making fome appli- 
cation of this principle, which may become ufeful to the arts. 
It has not yet. been fufficiently explained, why fome animal 
and vegetable matters produce carbon fo difficult to be inei- 
nerabade why charred pit-coal, known under the name of 
coke, or cinders, and which has been half burnt in the pre 
paration, is, however, fo powerful a combuftible; why peat, 
or turf, the weakeft of combullibles, acquires, by being pro-= 
perly charred, the property of welding large pieces of iron 
better than charcoal; and why, in the laft place, charcoal; 
when expofed to a very ftrong heat in’ veffels impenetrable 
to 
