C H E M I 
deranged, or that the vacuum is not perfect. The air, 
the relative weight of which in regard to atmofpheric air 
you tvilli to afeertain, is to be introduced into the bal¬ 
loon, and the weight marked air, is to be moved along 
the beam, The divilion at which it hands when an equi¬ 
librium is produced, will indicate, in hundredth parts of 
the weight of the volume of atmofpheric air that could 
be contained in the balloon, the weight of the gas a£hi- 
ally inclofed in it. This indication is read on the ante¬ 
rior part of the beam, where the words atmofpheric air are 
marked. 
Not fatisfied with having procured to philofophers, and 
thole fond of accurate experiments, an inftrument ex¬ 
tremely convenient for the clofet, and of very extenfive 
nfe, C. Paul has endeavoured to render this apparatus 
portable, and has conftrufted various pocket heel-yards, 
with which the nicelt experime'nts, may be made, and the 
quality of gold coin be afeertained by the trial of its fpe- 
cinc gravity. They are conhrufted exaftly on the fame 
principles as the Roman heel-yard, but are neceffarily 
lefs exteniive in their ufe. They cannot be employed, 
for example, in determining the fpecific gravity of an 
aeriform fluid, and do not extend beyond ioo deniers of 
weight; but as they poh'efs all the advantages of a balance, 
befides thofe peculiar to themfelves, they are extremely 
convenient for philofophers who are obliged to travel. 
APPARATUS for the COMBUSTION of the 
DIAMOND. 
That the diamond is combufiible, is a fa£l which New¬ 
ton, in fome meafure, conjeblured j which experience has 
fully confirmed; and refpefting which it is no longer 
pollible to entertain the leaft doubt. The experiments 
for ehablifhing this truth, have been recently made by 
C. Guyton, and in whofe words we fhall give the detail. 
“ My firft experiments, publifhed in 1785, on the entire 
combuftion in nitre in fufion, feemed to announce that 
the diamond burnt in it after the manner of coal, fince 
it left an effervefeent alkali; and this fufpicion acquired 
more reality, after the examination made by Lavoifier of 
the gas remaining in the vefl'els in which it had burnt, 
.and which he found charged with carbonic acid. Mr. 
Tennant has fince furaifhed us with a new proof of this 
important fabl, by repeating the combuftion of the dia¬ 
mond by nitre in a gold crucible, as I had propofed, in 
order to obtain a refiduum abfolutely free from all fo¬ 
reign matter. There were, however, Hill fufiicient rea- 
fons to induce us to difbeiieve that the diamond and 
carbon, or that the diamond and the carbon extrabled 
from the carbonic acid by the noble experiment of Mr. 
Tennant, were the fame fubftance. Independently of 
their external charadlers, fo completely different, feveral 
obfervations', which I have already communicated, prove 
that their chemical charableps no lefs excluded this iden¬ 
tity. Indeed if the diamond was pure carbon, why had 
it not the fame affinities ? Why does it not, like it,"ferve 
to make the oxygenated muriat of poiafh detonate; to 
deoxygenate fulphur, arfenic, and phofphorus ; to de- 
oxydate metals, which are fufficiently fixed to undergo 
the degree of fire which determines its combination with 
oxygen? Why does it not form alio carbures ? Why 
does it not, like it, conduit the eledtric fluid ? We know 
that the aggregation conceals fometimes the affinities by 
counterbalancing their power, but not in operations 
where the bodies are fufficiently fixed, and the tempera¬ 
ture fufficiently high, to render effedtual the weakell at¬ 
tritions. Something remained, then, to be difeovered 
to harmonize and make us comprehend fadts in appear¬ 
ance fo contrary. 1 imagined that it was by attentive 
cbfervation of what took place during the adt of the com¬ 
buftion of the diamond, that we fhould attempt to pene¬ 
trate this fecret of nature. The experiments I am about 
to deferibe will, I hope, prove that my attempt has not 
been vain ; that the explanation of phenomena, which 
have appeared to us the moil incoherent, may hereafter 
S T R Y. 387 
be deduced from fome circumftances which were not ob- 
ferved nor even lufpedted, and which have enabled us to 
make an important ftep in the knowledge of the nature of 
the diamond, fince we can indicate fubftances which ap¬ 
proach much nearer to it than carbon. 
Thefe experiments occupied a part of two fucceffive 
years. Various accidents, which may be readily con¬ 
ceived, and the fewnefs of the days when the rays of the 
fun are not interrupted by clouds, or weakened by va¬ 
pours, were the principal caufes of this delay. I fhall 
fupprefs the details of thofe efl'ays which did not lead to 
con'clufive relults; but I fhall not negieCl thofe which 
furnifhed us with an opportunity of obferving feveral 
times the fame fadls, and fometimes' in a more diftindl 
manner; though, by the effeft of fome unforefeen cir- 
cumftance, it was not poffible to keep an account of them 
in regard to the correfpondence of the ingredients and 
the produdls. I mult not omit to remark, that I had, as 
co-operators.in thefe experiments, C. Clouet, and Ha- 
chette. The journal of them was correctly kept by C. 
Deformes, formerly a pupil of the Polytechnic School. 
The moll important phenomena were feen, at different 
fittings, by feveral men of letters. 
The council of the adminillration of the Polytechnic 
School, approving the objedl of the experiments, autho- 
rifed me to ufe fome of the diamonds.in its cabinet. The 
firft experiment was made on the 9th of Fruftidor, in 
1797, or fifth year of the republic. We placed upon the 
table of a mercurial pneumatic ciftern, C, a bell of flint- 
glafs, as at D. Near the ciftern was placed, on one fide, a 
pneumatic machine, to exhauft the common air from the 
bell by means of a bent tube, which rofe as far as the 
knob, A. On the other fide was a water pneumatic ciftern, 
bearing a large receiver, having at its tubulure a cock, E, 
which communicated with the infide of the bell by a 
tube of bent glafs, and riling, in the like manner, to the 
hollow knob of the bell. On one of the edges of the 
mercurial ciftern was fixed a Hide, F, bearing a kind of 
mandril, deftined to receive a cylinder of hard wood, G, 
moveable in every diredlion, terminated by a handle of 
iron, H, and ferving to fupport the cup, I, made of the 
crucible earth of Valogne ; lb that this cup could be con¬ 
veyed to every point of the interior part of the beil- 
glals, to reprelent the diamond to the focus. This appara¬ 
tus is reprefented in the Chemiftry Plate X. fig. 2. Every 
thing being dilpofed in this manner, we put into the cup 
an incomplete oflahedral diamond, having the edges a 
little rounded, of a dirty water inclining to yellowifh- 
grey. O11 the cup, the edge of which was ground flat, a 
cover was applied, attached to a thread tied round the 
lower part of the fupport. 
A fmal'l air-pump, K, was made to adl, till the mercury 
in the bell-glafs role to near the orifice of the tubes of 
communication. - The cock of the receiver of the mer¬ 
curial pneumatic ciftern, which had been previoufly filled 
with oxygen gas obtained from the oxygenated muriat 
of potafh, was then opened; and the firft portion of this 
gas which had palled into the bell, was extracted by the 
pump, in order to exhauft, as much as poffible, the re¬ 
mainder of common air. After this it was filled with the 
fame gas to within iixty-nine millimeters ol its internal edge, 
and fifty-one of the external. It may readily be con¬ 
ceived that ltill a little air remained in the cup in which 
the diamond was placed, and which, during thefe experi¬ 
ments, had been (hut by its cover; but its content not 
being all together three cubic centimeters, this inconve¬ 
nience was thought the fmalleft of thole which were to 
be apprehended. 
The diamond having been uncovered, we began, at 
ten minutes after one, to throw upon it the folar rays, 
through the focus of the large lens belonging to the.ca- 
binet of the Polytechnic fchool. We are well aware of 
the neceffity of heating the bell-glafs by degrees, to pre¬ 
vent its cracking. For this purpofe we intefpoled, at 
firft, green and blue coloured glafs 5 but whether they 
acquired 
