432 Some Experiments on the Combustion of tlie Diamond. 



that a quantity of moisture not capable of being weighed by a 

 balance sensible to the -, ,}g- of a grain, is rendered evident by 

 deposition on a polished glass surface*. 



The diamonds were always heated to redness before they were 

 introduced into the capsule. 



During the combustion of the diamond, the glass globe was 

 kept cool by the application of water to that part of it imme- 

 diately above the capsule, and where the heat was greatest. 



In the first experiment, three diamonds, weigliing together 

 1'63 grain, were entirely consumed, in a quantity of oxygen gas, 

 more than three times as much as was necessary to convert 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 ori- 

 ginal temperature, there was a very evident deposition of mois- 

 ture ; but on arranging the apparatus, so as to ascertain the 

 change of volume of the gas, there entered only twentj-one 

 grains of mercury. In this experiment, the cylinder of platinum 

 had been fastened into the stop-cock by means of a small per- 

 forated cork : it seemed probable, when the small diminution 

 of gas was considered, that the appearance of moisture might be 

 owing to the ])ro(luction of vajiour from this cork during the 

 combustion, and the second experiment demonstrated that this 

 yidA the case. 



In this second experiment 1-S4 grain of small diamonds were 

 employed, a7ul aglass globe of the capacity of 149 cubical inches. 

 Soon after the capsule was placed in the focus in bright sunshine, 

 the diamonds burnt with great brilliancy, and continued to bum 

 till they had considerably diminished in bulk ; but their splen- 

 dour of combustion gradually became less, and before they ha^. 

 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 w-as 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 tlic fourth time they seemed incapable of burning, and 

 though kept for some minutes in the focus, appeared to under- 



* A piece of paper weigliing a grain was introduced into a tube of about 

 the capacity of four cubical inches, the exterior of vvhich was s^ntiy iicated 

 by a candle; immediately a slight dew was perceptible in tlie interior of 

 tlie nppcr part of the tube; the paper taken out and weighed immediately 

 in tlie balance above referred to, had not suffered any appreciable diminu- 

 tion. 



