on ithe Combuftion of the Diamond. 183 
Hie diamond will be’ to charcoal what azot is to nitrous yas. 
There will, therefore, be no longer occafion of wonder that 
more oxygen is neceflary to that fubftance, which as yet has 
none of it, than to that which has already been united with the 
quantity neceflary for arriving at the fir{t point of faturation. 
The fecond confideration refs on facts no lefs conclufive. 
Plumbago is a carbonacecus combutftible, which does not burn 
but at a very high temperature, er in nitre in fufion; which 
produces by its combuttion carbonic acid; which, as well as 
the diamond, is more abundant in combuftible matter than 
carbon itfelf. We are indebted to the illuftrious Scheele for 
the fir obfervation of this fact. One part of carbon alca- 
lifes only five parts of nitre; ene part of plumbago can alca- — 
life ten. The operation performed im a retort on $0 centi- 
grammes of plumbago, gave him 357 cubic centimetres of 
carbonic acid gas*. This agreement will not be contefted 
by thofe who, having been witneffes of our experiment, fo 
- unanimoufly declared, that the furface of the diamond af- 
fumed inftantaneoufly a leaden colour. 
This mineral is not the only body which prefents thefe 
ftriking charatters of a fubftance almoft incombuftible, and 
yet very. abundant, in combuftible matter. I defcribed, fix- 
teen years ago, in the Memoirs of the Academy of Dijon, a 
foffil found in a mafs in the coal-pits of the Rive-de-Gier, 
which was fent to me under the name of incombu/izhle coal, 
and which I then confidered as real coal which had paffed 
to the {tate of plumbago. I charaéterifed it in that manner. 
Our brother Dolomieu has defcribed a foffil of the fame 
kind, which he calls.carbure of alumine, which is the an- 
thracolite of Werner. I had already fufpected that it was 
' neither the prefence of feur or five centiemes of alumine, nor 
that of a ftill fmaller quantity of iron, that rendered it in- 
combuttible, but the little advanced ftate of the oxydation of 
the carbon. I fubjeéted it to two experiments, by which this 
was fully confirmed. 
The object of the firft was to determine if the alumine 
prefent was in a flate of combination fufficiently intimate to 
* Mem, de Scheele, French edit. Vol. II. p.27 and 29. 
g refift 
¢ * 
