i 9 4 C H E M ] 
as reprefented at fig. 9, in the fecond chemiltry plate. It 
eonfifts of a ciftern of wood, lined with Iheet lead, on 
tinned copper about two feet long, fixteen inches wide, 
and thirteen deep; at one end of which mull be placed a 
ihelf, having feveral holes in the nature of funnels, over 
which the jars and other velfels are to be placed in pneu- 
matical experiments. When this apparatus is ufed, the 
tub is to be filled with water to fuch an height as to rife 
about one inch above the upper furface of the Ihelf. The 
glafs jars are to be inverted with their mouths downwards 
upon the fnelf. If tliefe, or any other velfels open only 
at one end, be plunged under the water, and inverted 
after they are filled, they.will remain full, notwithftand- 
ing their being raifed out of the water, provided their 
mouths be kept immerfed : for in this cafe, the water is 
fuftained by the prefi'ure of the atmofphere, in the fame 
manner as the mercury in the barometer. It may without 
difficulty be imagined, that if common air, or any of the 
gafes, be fuffered to enter thefe veffels, it will rife to the 
upper part, and the furface of the water will fubfide. If 
a bottle, a cup, or any other velfel, in that ftate which is 
ufually called empty, though really full of air, be plunged 
into the water with its mouth downwards, fcarcely any 
water will enter, becaufe its entrance is oppofed by the 
elafticity of the included air; but, if the veifel be turn¬ 
ed up, it immediately fills, and the air rifes in one or 
more bubbles to the furface. Suppofe this operation to 
be performed under one of the jars which are filled with 
water, the air will afcend as before ; but, inftead of efcap- 
ing, it will be detained in the upper part of the jar. In 
this manner, therefore, we fee that any of the elaftic fluids 
may be emptied out of one veflel into another by an in¬ 
verted pouring, in which the air or gas is made to afcend 
from the lower to the upper veflel, in which the experi¬ 
ments are performed, by the aftion of the weightier fluid, 
exaftly fimilar to the common pouring of denfer fluids, 
detained in the bottoms of open veflfels, by the Ample 
aftion of gravity. To this apparatus, at A, is affixed a 
glafs bottle, whofe bottom is blown very thin, that it 
may fupport the heat of a candle fuddenly applied, with¬ 
out cracking. In its neck is fitted, by grinding, a tube, 
curved nearly in the form of the letter S. This kind of 
veflel is very ufeful in various chemical operations, for 
which it will be convenient to have them of feveral fizesr 
In the figure, the bottle is reprefented as containing a 
fluid, in the aft of combining with a fubltance that gives 
out gas, which paflfes through the tube into the jar B, 
under whofe mouth the other extremity of the tube is 
placed. At C is a retort of glafs, or earthen-ware, whofe 
neck being plunged in the water, beneath the jar B ; is 
fuppofed to emit the elaftic fluid, extricated from the 
contents of the retort, which is received in the jar. At 
D is a brafs cock, to let ofF the water when needful. 
In order to expel the gas from folid fubftances by means 
of heat, a gun-barrel, with the touch-hole fcrewed up 
and rivetted, may be ufed inftead of an iron retort. The 
fubjeft may be placed in the chamber of the barrel, and 
the reft of the bore may be filled with dry fand, that has 
been well burned, to expel whatever air it might have 
contained. The ftem of a tobacco-pipe, or a fmall glafs 
tube, being luted in the orifice of the barrel, the other 
extremity mult be put into the fire, that the heat may 
expel the gas from its contents. This gas will of courle 
pafs through the tube, and may be received under an in¬ 
verted veflel, in the ufual manner. But the moll accu¬ 
rate method of procuring gas from divers fubftances by 
means of heat, is to be put them, if they will bear it, 
into phials full of quickfilver, with the mouths inverted 
in the fame, and then throw the focus of a burning lens 
or mirror upon them. For this purpofe, their bottoms 
Ihould he round and very thin, that they may not be 
liable to fly with the violent application of heat. Many 
gales combine with water, and therefore require to be 
treated in an apparatus in which quickfilver is made ule 
©f. This fluid being very ponderous, and of confidera- 
1 
S T R Y. 
ble price, it is an objeft of convenience as well as econo¬ 
my, that the ciftern Ihould be fmaller than when water 
is ufed. But, as wood is permeable to mercury, it is to 
be feared, if the ciftern be made of wood, that the junc¬ 
tures may feparate, or the mercury efcape through the 
crevices ; if glafs, earthenware, or porcelain, be ufed, 
there is a rifk of its breaking. After feveral trials of 
different materials, Lavoifier found marble to be the bell 
fubllance for conftrufting the mercurial ciftern, which 
is perfeftly impenetrable by mercury, and not fubjeft to 
any of the inconveniences attending the other fubftances 
wq have juft mentioned. One of thefe fmall mercurial 
cillerns is delineated at fig. to, in the plate. Fig. 11, a 
feftion of the fame, to fhew the retort and receiving jar. 
Gales are either extrafted by the aftion of fire, or by 
means of acids. When difengaged by means of fire, a 
retort is always ufed : a bent tube is alfo to be adapted 
to the orifice of this retort, whofe extremity is plunged 
into the water or the mercury of the pneumatic ciftern, 
under a jar filled with the fame fluid, as fliewn in the fi¬ 
gure. When gafes are feparated by means of acids, we 
make ufe of phials or bottles, with one or with two necks, 
having tubes adapted to them. To this end, perforate 
a cork with a round file, and infert a bent glafs tube 3 
lute the joints well and clofe. This apparatus is not ex- 
penfive, and it is eafily prepared. 
To tranfmit gafes from one veflel to another, it is ne- 
ceffary, 1. That the latter be full of water, or fome fluid 
heavier than air. 2. That the aperture of the veflel be 
turned down, and cover the hole in the Ihelf of the cif¬ 
tern, as reprefented in the plate, at fig. 9. Things being 
thus difpofed, reverfe alfo the veflel which contains the 
gafeous fluid, and plunge it perpendicularly into the wa¬ 
ter of the ciftern, as lhewn in the pneumatic apparatus 
at E ; then, luppoling this veil'd to be corked like a bot¬ 
tle, uncork it in the water, and Hope it fo that its neck 
may Hick under the excavation of the flielf. The gas 
prefently el'capes from the bottle, and paflfes into the jar 
dellined to receive it; there it rifes in the form of bubbles, 
which burft at the top of the veflel, and drive out a pro¬ 
portionable quantity of the liquid contained therein. In 
whatever manner the operation is performed, the necef- 
fity of the excavation under the Ihelf mull be evident; 
it is dellined to receive the gas which efcapes from the 
immerfed jar, and to direft it towards the veflel which is 
to contain it; otherwife the gas which efcapes from the jar 
would bejfpread over the whole cavity of the ciftern, inftead 
of being carried to the place of its deftination. Lavoifier 
and others have contrived inllruments for meafuring the 
volume of gales, to which they have given the name of 
gafometer ; of which we lhall hereafter give a figure <md 
defeription. 
The firft of the elaftic fluids which ought to engage 
our attention, is oxygen gas. To extraft oxygen gas 
from luper-oxygenated muriat of potalh, put a quantity 
of this muriat into a glafs or earthen retort; adapt a bent 
tube, the other end of which is to be plunged into the 
pneumatic ciftern, under the jars or decanters. When 
the apparatus is in proper order, heat the retort, and in- 
creafe the aftion of the caloric by degrees. The oxygen 
gas is thus difengaged; and is commonly very pure. 
There is another very Ample method of procuring this 
gas. Put into an apothecary’s phial three parts of oxyd 
of manganefe in powder; pour in two parts of concen¬ 
trated lulphuric acid, or rather as much as is neceflary to 
make a foft thin palle ; cork the phial; the cork is to be 
perforated in the middle, and one end of a hollow bent 
tube is to be introduced, while the other end opens under 
the excavation in the Ihelf of the ciftern. When the appa¬ 
ratus is thus prepared, expofe the mixture in the phial to a 
gentle heat. Then heat, eft'ervefcence, and dilengagement 
of oxygen gas, takes place of the water contained in the 
jar placed for that purpole. To obtain oxygen gas from 
the leaves of plants, fill a bell-glafs with water, pafs the 
leaves underneath, and place thisglals in a veflel contain¬ 
ing 
