Encyclopaedia Britannica > Volume 7, ETM-GOA

FIX [ 280 1 FIX
Fixed Aii*. •which, with feveral others, were put into the middle
part of Nooth’s machine. Here it continued till
the roth of May. The effervefcence was frequent¬
ly renewed; for the firft: four days twice, and then
once a-day ; but the difcharge of air was continually
going on. It continued ten days without any figns of
decay; and when taken out of the machine on the 14th
day, though Tome of the older flowers were fading, the
others were as frefh and blooming as when put into
the veffcl; more fo than thofe which had been purcha-
fed on the fame day, and planted in the garden. The
body of the plant was green, fucculent, and undecayed.
The airextinguifhed flame. On trial it was found to be
one-third fixed air ; and during feveral days, the pro¬
portion of fixed air muft; have been larger.
■ But, when confined in veffels of fixed air, or even in
Nooth’s machine, with the upper part and grooved
ftopper put on, plants died fooner than in common air.
12 The air meafured was feven-eighths fixed air.
Phlogifton “ I am informed (fays Mr Henry), that an ingeni-
the food of ous philofopher of Geneva has made fome experiments,
” 1 ’ by which he has proved, not only that phlogifton is
the food of plants, but alfo, to the fatisfaCtion of Dr
Prieltley, that it is in the form of fixed air, in pro¬
per proportion and place, that this pabulum is admini-
Itered. In regard to the animal body, it would furely
be wrong,to fay that nothing was nutritious orfalutary
to it which it could not bear to receive unmixed or un¬
diluted. Why then may we not fuppofe, that though
fixed air, when pure, may be fatal to plants confined
in it, and excluded from communication with the ex¬
ternal air ; yet, when applied in a proper dofe, and to
plants enjoying a free intercourfe with the atmofphere,
it may have a contrary effeft, and ferve to nourilh and
fupport them ? But in Dr Prieftley’s experiments, this
free intercourfe does not appear to have been allowed ;
and herein, I apprehend, confifted the caufe of the dif¬
ference in our refults.
“ At that time the conftitution of fixed air was not
underftood. It is now generally allowed to be form¬
ed by a combination of phlogifton with the pure part
of atmofpheric air. The firft of thefe ingredients has
been proved by Dr Prieftley and others to be favour¬
able to vegetation ; while plants droop and decay when
expofed to the a&ion of the latter. It (hould further
appear from Dr Ingenhoufis’s experiments, that plants
have the power of feparating phlogifton from common
air, applying it to their nurture (a), and throwing out
the pure or dephlogifticated refiduum as excrementiti-
ous. Now allowing, what is highly probable, that
they hare a fimilar power of decompofing fixed air,
and of applying and rejedfing its conttituent parts, our
method of conducing the experiments was not inju¬
rious to the procefs; whereas, when confined in clofe
yeflels, as by Dr Prieftley, the plants would be fuffo-
cated in a manner reverfed to what would happen to an
animal. For as in that cafe, from a want of commu¬
nication with the atmolphere, as neceffary to carry off
the phlogiftic air from the lungs (according to the beau¬
tiful theory of refpiration advanced and fo well fupport-
ed by Dr Pueftley), the animal muftperilh ; fo, in the
other inftaoce, the plant would die if cut off from the air
of the atmofph&re in fuch a manner that the .pure air ex-
N° 127. - . .
creted by its veffels would not be conveyed from it. Fixed Ain
For in thefe circumftances, this fluid, fo falutary to ani- —-J
malbut deftru&ive to vegetable life, muft be aecumula-^ ,
ted in the body of the plant; and its fun&ions being-
thus impeded, death is the neceflary confequence.” ting water
As fixed air is now an article of the materia medica,or other li-
a method of obtaining it readily and in large quantity ^ll0rs m
becomes an objeft of confiderable confequence. Mr with"
Henry, who has proved that fixed air is the proper fixed air.
bafe of ferments, and the immediate caufe of fer¬
mentation f, defcribes an apparatus for impregnating tSee-fer-
wort or other fermentable liquors with it. This appa- mentatton‘
ratus is reprefented Plate CXCIII.
ji A, Fig. 1. reprefents the cafk in which the wort
is to be impregnated; dd, the firings by which the
air-veffel is to be let down.
Fig. 2. DD, The air-veffel, fimilar to the bottom
part of Dr Nooth’s glafi? machine, to be made of glafs
or earthen ware, cc, A glafs-ftopper ground in to fit
the mouth of the veffel, having a number of capillary
tubes running from bottom to top in a diverging di¬
rection, fo as to fpread the air in its paffage through
the liquor.
Fig. 3. The ftopper viewed feparately to /how the
capillary tubes.
The method of ufing this apparatus is obvious from
an infpe&ion of the figure; but at the fame time it
muft be equally evident, that it cannot be applied where
any very large quantity is to be impregnated. Where
great quantities of fixed air are required, we muft alfo
ufe great quantities of fermenting materials ; and it
would be inconvenient in the higheft degree to immerge
thefe in the liquor to be fermented ; not to mention,
that where large quantities of this kind of materials
are mixed, they ought frequently to be ftirred or fhaken,
left they fhould concrete into hard lumps ; while at the
fame time they are often apt to fwell, and would thus
endanger the fpoiling of the liquor altogether. It
muft alfo be remarked, that any liquid receives an
impregnation of fixed air more readily from the
furface than by blowing it through the mafs of li¬
quid. The apparatus reprefented fig. 4. therefore fcems
preferable to that of Mr Henry, as capable of being
extended indefinitely almoit without any additional
trouble. ABGD reprefents a large wooden cafk filled
with materials to the height reprefented by k k.
£ is a large flat cooler for holding the liquor to be im¬
pregnated. This veffel is to be clofely covered, and
may be conveniently made of lead, having a wooden
top, the edges of which are clofely luted all round with
a mixture of falad oil and finely powdered chalk.
fi Reprefents a tin pipe, about an inch in diameter, by
which a communication is made between the cafk and
cooler for the tranfmiffion of the fixed air. ^ Is a
wooden axis pafiing quite through the 'cafk from top
to bottom, and moveable on a centre h, having a ftrong
handle at top, to turn it in order to ftir the mixture.
i i it, Are four crofs blade? fixed into the axis, which,
in confequence of turning the handle, ftir and raife a
great commotion in the liquor contained in the cafk.
m, Is a large hole flopped with a wooden plug, by
which the materials may be put in or taken out ; and
for this laft purpofe a kind of ladle with an upright
ft era
(a) See this further difcuffed under the article Aerology, n° 51, 52.