186 Experiments made-at the Polytechnic School 
combuftions of the diamond by the folar fire, and the expe- 
timents which followed :— 
1. It is not only by the colour, weight, hardnefs, tranf- 
parency, and other fenfible characters, that the diamond 
differs from charcoal, as feems hitherto to have been be-. 
lieved ; 
Om Nav is it by the ftate alone of the aggregation of the 
matter that conftitutes diamond : 
3. Neither. is it gn account of the 20oth part of the cine- 
ritious refiduum left by carbon, or the {mall quantity of Bye 
drogen which it contains. 
4. It is more effentially by its chemical properties that it 
differs. 
5. The diamond is the pure combutftible fubftance of this 
genus, 
6. The produé& of its combuftion, or of its combination 
with oxygen to faturation, is carbonic acid without refidue. 
4. Carbon burns at a temperature eftimated at 188° of the 
centigrade thermometer ; the diamond does not inflame but at 
abact. 30 pyrometric meal which, according to Wedge- 
wood’s feale, makes a difference of 188 to 2765. 
8. Charcoal, when kindled, maintains of itfelf, in oxygen 
gas, the temperature neceflary for its combuftion, The com- 
buftion of the diamond ftops when you ceafe to maintain it 
by a furnace-heat, or the union of the folar rays. 
g. The diamond, for its complete combuftion, requires a 
much greater quantity of oxygen than charcoal does, and 
produces alfo more carbonic acid. One part of charcoal ab- 
forbs in this operation 2°527 of oxygen, and produces 3°575 
of carbonic acid. One of diamond abforbs a little more than 
four of oxygen, and really produces five of carbonic acid. 
10. There are fub{tances which are in a ftate of interme- 
diary compofition between the diamond and charcoal. Thefe 
are plumbago, or native carburet of iron ; incombuitible fofiil 
coal; the carburet of alumine of Dolomicu ; the anthracolite 
of Ww erner; the black matter united to iron in the ftate of 
caft iron and fteel ; carbonaceous refiduums difficult to be 
incinerated ; and carbon itfelf unburnt, (d/drulé,) by the 
action of a ftrong heat without the contact of air. . 
9 11. Thefe 
