380 CHE M. ; 
Sciences for 1777. In my experiments I have generally 
burnt fixty grains of pbofphorus. They have (hewn that 
the weight of the phofphoric acid produced, is always 
.nearly equal to that of the pbofphorus burnt, and of the 
oxygen gas employed. I calculated the refults by the 
method defcribed by Lavoifierin his Treatile of Chemif- 
try (vol. ii) ; but it is not'neceflary they fliould be in¬ 
ter ted here, as the compofxtion of the phofphoric acid 
has been diffidently eflablilhed by the accurate experi¬ 
ments of Lavoilier. My objedl, in deficribing the appa¬ 
ratus I employed, was merely to enable thole who wifli 
to repeat the experiments, to do fo by an eafier method, 
and with more certainty than according to that propofed 
by him. It mull here be obferved,that as the pbofphorus 
by my proeefs, inflames in rarefied air, there is no dan¬ 
ger that the hidden expanlion of the air, produced by the 
intenfe heat of the inflamed phofphorus, will built the 
glafs, to,prevent which, in Lavoifier’s method, requires 
great caution, as he himfelf has remarked. That the 
balloon during the combullion may be as little heated as 
poffible, I fuller the air, after the inflammation, to pafs 
gradually, and in fmall quantity, into the glafs globe, 
and for that reafon do not open the cock until the flame 
begins to be extinguiffied. In this manner the experi¬ 
ment may be performed without any danger. 
“ In the year 1794, I made known, in the thirteenth 
number of th eCbemifchen Oejfeningen of the celebrated Klaf- 
tellyn, my experiments on the combullion of phofphorus 
in the fo-calLed vacuum of an air-pump. Had profeflor 
Gottling, and other German chemifts, who have obferved 
phofphorus to ffiine in azotic gas, paid more attention to 
what thefe experiments clearly eftablilh, they would not 
have made fo much noife refpedlinga phenomenon which 
is fo like the Alining of phofphorus before it inflames in 
air highly rarefied. This ffiining of phofphorus in an 
imperfedl vacuum, Ihews, that the fmall quantity of oxy¬ 
gen gas contained in atmolpheric air lo highly rarefied, 
is Hill fufficient to occafion that luminous appearance; 
and, as it is well known that it is abfolutely impoflible to 
produce azotic gas which does not contain fome oxygen 
gas, they might have feen by thefe experiments, that the 
fmall quantity of oxygen which mull have been contained 
in their azotic gas, was fufficient to produce that light 
which they obferved. 
“ I (hall here only add, that phofphorus will not fliine 
at .all in azotic gas which contains no oxygen gas. This 
I ihewed, on the 18th of January 1794, in ray leisures 
at the Teylerian Inllitute. I introduced azotic gas over 
mercury, and freed it totally from oxygen gas, by intro¬ 
ducing phofphorus into it on the point of a bent iron 
wire, which I pafled up through the mercury, fo as to 
bring the phofphorus in contadl with a piece of ignited 
iron previoufly introduced into the receiver. All the 
oxygen gas united itfelf in a moment with the volatilized 
photphorns ; and another bit of phofphorus, which after 
the cooling of the apparatus I made to rife through the 
quickiilver into the azotic gas, which in that manner 
was freed from all oxygen, did not ffiine, A fmall bub¬ 
ble of atmolpheric air was fufficient to reproduce the 
ffiining. It was then feen diffufed throughout the whole 
gas, in the fame manner as when atmolpheric air is ad¬ 
mitted into an exhaufted receiver, in which phofphorus 
has ceafed to be luminous. I Ihewed, in the courfe of 
the fame ledlure, that phofphorus does not fliine in a per-, 
fedl vacuum. For this purpofe I caufed the phofphorus 
to ai'cend through the quickfllver of a barometer, and it 
exhibited no light, ’in order that this experiment may 
completely fucceed, you mull employ a barometer, the 
tube of which has been well freed from atmofplieric air, 
by boiling the'quickfilver in the tube. If you ufe a ba¬ 
rometer the quickfllver of which has not been boiled, the 
fmall quantity of air contained in it will be fufficient to 
make the phofphorus luminous ; but this appearance will 
be of fliort duration, becaufe the exhaufted fpace of fuch 
1 
S T R Y. 
a barometer can contain only a very fmall quantity of 
oxygen gas.” 
The MERCURIAL GAZOMETER of W. H. 
PEPYS, Jun. 
The difficulty which has attended the exhibition of 
acid and alkaline gafes, was the firft inducement to 
Prieftley, Lavoilier, and others, to ufe mercury for fuch 
experiments; but the great expence and enormous weight 
of this fluid, obliged many accurate and experienced 
chemifts to relincjuifii them almoll entirely, as there ap¬ 
peared no other iikely means of fucceeding but by its 
means, and that of the exhaufted receiver. A contri¬ 
vance to leffen the quantity of mercury neceflary for fuch 
experiments, is therefore a defirable objedl; and Mr. 
Pepys feems to have fucceeded in conftr.udling an appa¬ 
ratus, in which the above-mentioned requiiites are ob¬ 
tained at a comparatively fmall expence; As it is hardly 
poffible to japan tin or copper fo perfectly as to prevent 
their being attacked by mercury when brought in contadl 
with them, the cylinders'are turned in lignum vitae, on 
which the mercury has no adlion ; the conducting tube is 
of glafs; and the cocks are coated on the infide with var- 
nifli. The ufefulnefs of an apparatus fo conllrudled will 
appear fufficiently obvious, when it is recolledted, that 
all gafes pafled through any other fluid than mercury, 
as water for inftance, take up a quantity of moilture, 
which adds confiderably to their gravity, and makes it 
impoflibfe to determine their real weight. 
For weighing the gafes, a glafs globe and llop-cock of 
a fmaller fize than is commonly employed, is here to be 
ufed, as greater accuracy can be obtained by ufing a 
proportionally delicate beam, than by employing a larger 
globe, which mull be fufpended to a beam of fuch ftrength 
as greatly to increafe the fridtion on its axis. It is of 
great importance in the analylis of bodies, or in other 
chemical experiments, to be able to afcertain with accu¬ 
racy the weight of any gas obtained by the proeefs. The 
weight of two or more quantities of gas fliould however 
be always tried, and the mean be taken, to prevent any 
error. 
Fig. 2, in the Chemiftry Plate VIII. is a reprefenta- 
tion of the bell-glafs of the gazometer, furnifhed with a 
cock at top, and able to contain thirty-four ounces troy 
of diftilled water. Thedivilions of capacity, determined 
by adlual meafurement, are marked on the glafs with a 
diamond. B B, fedtion of two cylinders of lignum vitae, 
the outward one ferewed upon the lolid internal one, 
which is made to projedt at its lower extremity, and fur- 
nilhed with a male ferew, to work into a female ferevr 
with which the lower end of the external cylinder is fur- 
nilhed. The fpace between thefe is fo adjufted, as to be 
almoll filled up by the fubftance of the bell-glafs A, 
when dropped into it, fo that the quantity of mercury 
neceflary to fill up that fpace is proportionally fmall. 
The internal cylinder has a condudting tube through its 
axis, the lower end of which is furnifhed with a female 
ferew anfwering to the male ferew of the cock of the fmall 
receiver C. The receiver C is made of glafs, and open 
at the bottom. When this receiver is ufed, it is ferewed 
into its place, and refts upon a fmall cup or cittern of 
mercury D, in which the beak of a retort, furnifhed with 
a bent glafs tube, may be introduced under the receiver. 
E, E, fedtion of a wooden Hand, upon which the cylin¬ 
ders of lignum vitae are l'upported, having an opening 
through the top, to permit the cock of the receiver C 
to'be joined to the condudting tube of the internal cy¬ 
linder B. The ciftern D is adjufted to its height by 
means of a riling cylinder in the pedeftal F. Fig. 3. is a 
transfer glafs for mixing alkaline gales in vacuo, or 
other purpofes; and, when ufed, is joined to the top of 
the bell-glafs A. Fig. 4. a glafs globe and llop-cock, 
capable of holding 14 ounces troy of diftilled water for 
weighing gafes; it receives its gas by being inverted. 
