ae 
on the Combuftion of the Diaindnd. 299 
fubjected tu the fame proof, in the fame proportions, with 
the fame nitrous gas. The refiduum this time was only 30 
"parts ; and as the 300 of nitrous gas employed cdutanaie 
“nine or ten parts for 2 of azot, we eonlased that this oxy- 
gen gas was quite pure,+=Thele are the words of M. Hum- 
boldt. 
When this firft donna” was fulfilled, the queftion chest 
was to place, iri the centre of this globe, the diamond def- 
tined for the experiment. We had previoufly formed a fmall 
cup of the lower portion of a furnace-pipe, the tube of which, 
five centimetres in length, was fixed to an iron ftalk, and this 
ftalk was {tuck into a cylinder of cork deftined to be inferted 
in the neck of the balloon. This cork was dipped in matftic 
to fhut its pores, and a {mall glafs tube pafled through it to 
eftablifh a communication’ between the infide of the balloon 
and the mercurial tub. (See fig. 2. Plate IT.) 
‘We then placed the diamond on the cup, where we left it, 
haying put it there by means ofa ribbon, which we drew from 
under it in an inflant, as foon as the balloon had been in- 
verted, and its neck immerfed in the mercury. The balloon 
in this pofition was made faft in a kind of collet, which 
tefted on the edges of an iron mortar that ferved as a hy- 
drargyro-pneumatic tub. We then exhaufted, by fuétion, a 
portion of the oxygen gas fufficient to make the mercury: 
rife to 12. centimetres above the orifice of the balloon. 
The diamond was the fame that had been already expofed 
to the action of the folar fire towards the end of the experi- 
ment of the preceding year, and which had loft only two 
deci-milligrammes, and confequently weighed 199: g milli- 
grammes (3°766 grains), or one carat wanting ~* 
On the 5th Fructidor laft year, at one in the Bicep okt 
we began to throw upon the diamond the focus of the large 
lens of the National Inftitute. . The thermometer, expofed to 
the fun under a bell-glafs, indicated 39°75: the mercury in 
the barometer ft0od at 75°89 centimetres, (28 inches 0-5 
lines.) The volume of air; inclofed by means of the mer- 
cury in the tub, brought to the preflure of 757°7 millime- 
* It is well known that the carat of the jewellers is only 205772 milli- 
grammes. 
VoL, V. Aa tres 
