CHEMISTRY, 
thefe conical pieces, before it is put in its place, to pre¬ 
vent all communication with the air of the atmofphere. 
The balloon, for the compofition of water, placed 
■Upon its tripod between the gazometers, differs from that 
of Lavoifier, principally in the manner of lbutting it, in 
order to prevent the entrance of air. For this purpofe 
there is a rim of copper a a, fig. 3. fixed on the neck of 
the balloon, by means of plafter of Paris, which, that 
it may afford no paflage to the atmofpheric air, is coated 
over with common cement or lute, above the edge of the 
banian:, as may be feen at bb-, and this cement is co¬ 
vered with a ftrip of linen c c, a quarter of an in-ph in 
breadth, dipped in the white of an egg mixed with lime. 
The rim of copper a a, has a copper ring d d, foldered 
to it at right angles; and on which the plate of copper 
e e is ground, in fuch a manner that it is fufticient to 
greafe (lightly the upper furface of the ring d d, when a 
vacuum is to be made, taking care to apply To little 
greafe that it may not,penetrate into the balloon. To 
exhauft the balloon there is a cock, which communicates 
by a bent tube with an air-pump placed behind the bal¬ 
loon; and to prevent the working of the air-pump from 
lliaking the balloon, this bent tube is made in part of 
elaftic gum. The plate of copper e e, is kept down upon 
the ring dd, by fix (crews; two of which may be leen 
at//, placed at equal diftances round the neck of the 
balloon, and by means of which the plate ee may be 
made to prefs very (trongly on the ring d d, on turning 
thefe (crews by the help of a key. Both of the gazo- 
meters are made to fhut in the fame manner. 
The inferior furface of the plate e e is covered, as far 
as it covers the opening of the balloon, by a thin plate 
of pure lilver, in order that the vapours formed during 
the experiment may not touch the copper. For the fame 
reafon the bent tube hn> in the balloon, is alfo made of 
pure filver. At the extremity of this tube, is a piece of 
platina, having a very fmall aperture, fcarcely fufticient 
to afford a paflage to a very fine needle. The part 
which ferves as a conduftor to kindle the hydrogen gas 
by an ele&ric fpark, is alfo made of platina, as far as it 
■is not inclofed in the glafs tube, 0 0, by which it is infu- 
lated. Platina is preferred for thefe two parts, in order 
to prevent the oxydation of the metal, which the heat, 
produced by the combullion of the hydrogen gas in oxy¬ 
gen, might occafion. The tubes pppp, which ferve to 
conduft the gales into the balloon, are made of glafs, and 
cemented into the copper tubes q q, which have conical 
extremities, like thole above defcribed, to fix them on 
the cocks. Thefe glafs tubes are raifed a little above the 
edge of the cylinder H, to prevent the water from palling 
into the balloon, Ihould we happen to fill one of the 
glafles A, and negleCl to Ihut well the cock C. 
It will be proper to make the glafles A, pretty large, 
if they can be procured fo, in order that the gazometers 
inay contain the more air. It will however be belt to 
make them rather high (twenty-eight or thirty inches) 
than wide, in order that the exaCtnefs of the fcale a b 
may not be diminilhed. M. Van Marum anfwers an 
objection, which he fays may pofiibly be urged againll 
this apparatus, namely, that the combullion is obliged to be 
lufpended every time that the gazometers need to be re- 
pleniftted with either oxygen or hydrogen. He fays this 
is no folid objection, as he finds that, fince he ufed pla-. 
tina for conveying the eleCtric fpark, he never fails to 
kindle the hydrogen the firft moment it enters the bal¬ 
loon ; and that, befides, the combuftion of a cubic foot 
of hydrogen gas, in order that the water produced may 
not contain acid, odght to take fix hours. Thofe who 
with to make experiments of longer duration, have only 
to attach two other gazometers; by which means, while 
the one let is emptying, the other may be repleniflied. 
For this purpofe it will be neceflary to have, inftead 
of the cock u, two cocks Z 1, Z 2, fig. 4, lcrewed to a 
piece of copper fixed to the cover of the balloon 5 and 
by which each of thefe cocks has a communication with 
379 
the bent tube Irn, by means of two holes x, x, which pro¬ 
ceed obliquely through this piece, and end in the tube/. 
The firft gazometer, which communicates with the bal¬ 
loon by the cock Z 1, being almoft emptied, the cock 
Z 2, of the fecond gazometer, may be opened, after hav¬ 
ing made the preflure in the fecond gazometer equal to 
that in the firft. It is evident that the preflures of thefe 
two gazometers being equal, the velocity with which the 
hydrogen gas enters the balloon will not experience the 
leaft change. When the firft gazometer is entirely empty, 
the cock Z 1 is fhut and the firft gazometer is filled ; and 
the cock Z 1 is not opened till a little before the fecond 
gazometer is totally emptied. The fecond gazometer is 
then to be filled again; and in this manner the combuf¬ 
tion of hydrogen gas may be continued by thefe gazo¬ 
meters to any length of time, without interruption. To 
introduce the oxygen gas without interruption into the 
balloon by means of two gazometers, it will be fufticient 
that the two cocks, which form a communJcation between 
the gazometers and the balloon, be immediately fixed in 
the covering of the latter. 
Both halves of the apparatus being fimilar, the letters 
of reference are only marked on one fide of the plate. 
VAN MARUM’s APPARATUS for the COMBUS¬ 
TION of PHOSPHORUS. 
This able chemift having made feveral fruitlefs attempts 
to render a balloon, for the combuftion of pholphorus 
in hydrogen gas, perfectly air-tight, according to the 
method defcribed by Lavoifier in his Elements of Che- 
miftry, he conftruCted another fimilar to that employed 
in his gazometer, above defcribed, for the compofition 
of water; and fecured it againll the entrance of air in the 
like manner. This apparatus is reprelented at fig. 1, in 
the Chemiftry Plate VIII. where the balloon A, has two 
cocks B C, with conical Hoppers, and united to the tubes 
by the fame means as thofe in the gazometer above-men¬ 
tioned. Within the balloon is a fmall crucible of pla¬ 
tina, d, fufpended by two wires of the fame metal, from 
the plate of copper by which the balloon is (hut. The 
cock B ferves to conneCt the tube with an air-pump, and 
by thefe means to empty the balloon of atmofpheric air. 
By the cock C, the oxygen gas, contained in the gazo¬ 
meter G, is introduced; but, as this gas ought to be as 
dry as poflible before it is admitted into the balloon, there 
is applied, between it and the gazometer, a glafs cylinder 
H, filled with a fait which ftrongly attracts the moifture 
of the gas. The fait found molt effectual in this expe¬ 
riment, was that ufed and recommended by Sauflure for 
drying atmofpheric air. It is the alkali which remains 
after the decrepitation of a mixture of equal parts of 
nitre and crude tartar, which has been kept at a red heat 
for an hour. 
The fait in the tube H mull not be pulverifed, but di¬ 
vided into fmall fragments, in order that the gas may 
penetrate through it, and come in contaCt with a greater 
portion of its furface. The tubes i, u , k, by which the 
cylinder H is connected with the gazometer and the bal¬ 
loon, muft be pliable, becaufe it would be too difficult 
to place the cylinder H in fuch a pofition, as to be united 
with the balloon and gazometer by means of tubes not 
capable of being bent. Pliable tubes of elaftic gum are 
bell for this purpofe, the ends of vvhich are faltened to the 
copper pipes lcrewed into the cocks. 
Lavoifier kindled the phofphorus in his balloon by a 
burning lens; but Van Marum oblerved that phofphorus 
wrapt up in a particular manner inflames fpontaneoufly 
when the air is rarefied to a certain degree ; and he em¬ 
ployed the refult of this obfervation to inflame the phof¬ 
phorus in his balloon. This chemift deferibes the utility 
of the prefent apparatus, as follows: “I have feveral 
times, both in the courfe of my lectures and on other 
occalions, (hewn the production of the phofphoric acid 
by the combuftion of phofphorus in oxygen gas, as de¬ 
fcribed by Lavoifier in the Memoirs of the Academy of 
Sciences 
