124 , 
Mr. Tennant on the 
experiments for this purpose. He exposed the diamond to the 
heat produced by a large lens, and was thus enabled to burn 
it in close glass vessels. He observed that the air in which 
the inflammation had taken place hud become partly soluble 
in water, and precipitated from lime-water a white powder 
which appeared to be chalk, being soluble in acids with effer- 
vescence. As M. Lavoisier seems to have had little doubt 
that this precipitation was occasioned by the production of 
fixed air, similar to that which is afforded by calcareous sub- 
stances, he might, as we know at present, have inferred that 
the diamond contained charcoal ; but the relation between that 
substance and fixed air, was then too imperfectly understood to 
justify this conclusion. Though he observed the resemblance 
of charcoal to the diamond, yet he thought that nothing more 
could be reasonably deduced from their analogy, than that each 
of those substances belonged to the class of inflammable bodies. 
As the nature of the diamond is so extremely singular,, it 
seemed deserving of further examination ; and it will appear 
from the following experiments, that it consists entirely of 
charcoal, differing from the usual state of that substance only 
by its crystallized form. From the extreme hardness of the 
diamond, a stronger degree of heat is required to inflame it, 
when exposed merely to air, than can easily be applied in 
close vessels, except by means of a strong burning lens ; 
but with nitre its combustion may be effected in a moderate 
heat. To expose it to the action of heated nitre free from ex- 
traneous matters, I procured a tube of gold, which by having 
one end closed might serve the purpose of a retort, a glass 
tube being adapted to the open end for collecting the air pro- 
duced. To be certain that the gold vessel was perfectly closed. 
