Encyclopaedia Britannica > Volume 7, ETM-GOA

FIX [ 279 ] FIX
Fixed Air. though as much ftill remain as would be fufficient to
fupport Ufe in other circumflances. Hence, if a
ftrong and healthy animal is fuddenly plunged into an
atmofphere loaded with mephitic or other noxious va¬
pours, it will very frequently die in a moment; while
the mere circumltance of debility caufes others to bear
Whyfud- the fame fituation with impunity. In thefe circum-
den changesllances a fudden expofure to very pure air might
from noxi. even ke fatal to an animal very long confined in fuch
air a replan 38 18 nox*ous> ju^ as ^re raa>r Put out t0° vi°lcnt
gerous. a hlaft of air. Hence we may uuderftand why con-
fumptive perfons are not recovered, but often made
manifeftly worfe, by being brought into purer air ; and
in all probability the death of Travis was hailened by
his fudden removal into the open atmofphere. His
remaining alive, therefore, for fuch a length of time in
circumftances fo very unfavourable, we are to attri¬
bute in a particular manner to the extreme debility of
the vital powers,by which an exceedingly fmall quantity
of dephlogifticated air was required to fupport them.
We arebefides to take into confideration, that in cer¬
tain cafes the air will impart nouriihment, even to the
bodies of animals as well as vegetables. Under the
article Abstinence, inftances are brought of animal
bodies being augmented in bulk without any nourifh-
ment taken in by the mouth. In fuch cafes we mull
IO conclude, that the nourilhment came from the phlo-
The human giftic particles difperfed through it. It is not im-
1 ody may poffible, therefore, that in fome cafes the human body,
abforb^ou ^7 abfoibing from the atmofphere the phlogiflon
rifhment° which it had jult emitted by refpiration, may purify
from the the air which it had juft before contaminated : and
atmo- thus life might be prolonged in the cafe of Travis, who
fphere. wag not oniy deftitute of air proper for refpiration,
but of food and drink alfo. In cafes of famine, it is
manifeft that there is a great abforption from the at-
nrofphere. Thus a negro who was gibbeted at Charlef-
town, and had nothing given him afterwards, voided a
large quantity of urine every morning ; and in cafes of
lientery and diabetes, the quantity of evacuations
greatly exceeds the nourifhment taken in by the
mouth. On this principle, perhaps, we may account
for that very ftrange phenomenon of animals being
found alive in the heart of folid bodies, where there
could be no pofirbility of any connexion with the ex¬
ternal atmofphere. inftances of thefe are given under
tl the article Animalcuxe, n° 57.
Effefb of We ftiall conclude this part of our fubjeft with fome
fixed air on obfervations made by Mr Henry on the effefts of fix-
vegetation. ed air on vegetation. Experiments on this fubjecl had
been made firft by Ur Prieftley, and afterwards by Dr
Percival, but with very different refults; the former
concluding that fixed air was prejudicial to the growth
of vegetables, and Dr Percival that it was favourable
to it. Mr Henry endeavours to reconcile the diffe¬
rence. He fuppofes Dr Percival’s meaning to be, not
that fixed air, in its pure ftate and ftagnant, was fa¬
vourable to vegetables immerfed in it; but that gra¬
dually applied, and in a continued ftream, while the
plants at the fame time are not confined from the com¬
mon air, do receive from fixed air fuch a proportion
of nouriftiment as is fufficient for their temporary fup¬
port, even when removed from every other means of
being fupplied with food.
Dr Prieftley, in his third volume on Air, acknow¬
ledges the fairnefs and candour with which the experi- t
ments of Dr Percival were related, but fuppofes there '
mull have been fome miftake ; particularly, as the air
was produced by Dr Nooth’s apparatus, he thinks the
quantity could not be fo great as was imagined. In
fupport of this opinion he mentioned a great number
of experiments, in which fixed air was tried in all pro¬
portions, from a ftate of purity to a mixture of one-
third of fixed air with feven-eighths of common air ;
and in all thefe the fixed air was found to be injurious,
and to dellroy the colour of rofe-leaves.
From fome experiments made by Mr Henry himfelf,
the contrary opinion feemed to be eftablilhed. By thefe
it appeared that a ftravvberry plant had not only been
preferved alive, expofed in the middle of Dr Nooth’s
machine to copious ftreams of fixed air, from the 23d
of April to the 14th of May, but that the bloffoms,
which were only budded when put into the machine,
had adlually expanded ; a ftrong proof that the plant
had continued to vegetate. It was ftill alive, but in
a fituation fomewhat drooping ; and happening to be
crulhed on taking it out of the apparatus, it was
thrown away altogether. Two fprigs of mint, with
fome earth loofely adhering to their roots, were fubjec-
ted to a fimilar experiment from the lit to the 12 th of
September ; the one having a continual current of fix¬
ed air applied to it, but the other being left to the
operation of common atmofpherieal air. The roots of
both were cut off on the 7th : that in common air ex¬
hibited fymptoms of decay on the 12th; but the other
continued frelh for more than a week after the other
had been decayed almoft to the top.
On the 1 ith ©f April 1777, the weather being;very
cold and backward, Mr Henry filled the middle part of
Dr Nooth’s machine entirely with fixed air, by firft
filling it with water, inverting it in the fame fluid.
Hopping up the capillary tubes, and then driving out
the water from the veffel by a ftream of fixed air from
an effervefeing mixture. The middle was then imme¬
diately placed in the lower part of the machine, con¬
taining an effervefeing mixture alfo, which had been
working for feveral minutes; and a crimfon polyan¬
thus was introduced into the middle part, and fufpend-
ed by a firing. In palling through the mouth of the
veffel, the petals were compreffed, and one or two re¬
ceived fome damage. A young fprig of mint, with its
root, was introduced the fame day, and into the fame
veffe! ; while a fimilar fprig, as a ftandard, was placed
in a large glafs decanter. The polyanthus began to
droop on the 15th, and was taken out next day ihri-
velled but not difcoloured. The mint, when examined
on the 12th, was apparently more frelh than when firft
put into the veffel with fixed air; the next day two
young Ihoots appeared ftill more vigorous. On the 15th
its appearance was more vivid than that in common
air; but next day it was taken out quite dead. This
fudden change, however, our author fuppofes to have
been owing to the machine having no valve ; and ha¬
ving been violently lhaken, he fufpefted that fome of
the vitriolic acid had been forced up through the tubes ;
for the moifture on the infide of the middle part was
found to be more acid than it Ihould have been by fix¬
ed air alone.
The experiment was repeated on the 26th of April
with a polyanthus plant with its root and flowers,
which.