CombustioJi of the Diamond. ^6i 
'gas, more than three times as much as was necessary to con- 
vert them into carbonic acid. In this case, after the combustion 
had once commenced, it continued without a fresh application 
of the lens till there remained only a very thin piece of the 
largest diamond in contact with the capsule, and this by being- 
brought into the focus, rapidly disappeared. On restoring the 
globe to its original temperature, there was a very evident 
deposition of moisture ; but on arranging the apparatus, so as 
to ascertain the change of volume of the gas, there entered 
only twenty-one grains of mercury. In this experiment, the 
cylinder of platinum had been fastened into the stop-cock by 
means of a small perforated cork ; it seemed probable, when 
the small diminution of gas was considered, that the appear- 
ance of moisture might be owing to the production of vapour 
from this cork during the combustion, and the second expe- 
riment demonstrated that this was the case. 
In this second experiment 1.84 grains of small diamonds 
were employed, and a glass globe of the capacity of 14.9 cu- 
bical inches. Soon after the capsule was placed in the focus 
in bright sunshine, the diamonds burnt with great brilliancy, 
and continued to burn till they had considerably diminished in 
bulk ; but their splendour of combustion gradually became 
less, and before they had apparently lost half of their volume 
the process ceased. By placing them a second time in the 
focus, after agitating the globe so as to change their places, 
the combustion was again produced ; but the light was much 
less vivid than before, and the combustion continued for a 
much shorter time. They were exposed to the concentrated 
rays a third and a fourth time, but after the fourth time they 
seemed incapable of burning, and though kept for some 
