?44 AERO 
counteract, in a great meafure, the damage done by ani¬ 
mal rcfpiration, combuftion, fee. is evident from thefe 
experiments. It may only be faid, that vegetation does 
not appear to be fufficient to remedy entirely that damage. 
.The power of vegetables in yielding dephlogiflicated 
air, begins a few hours after the fun has made its appear¬ 
ance in the horizon, or rather after it has palled the me¬ 
ridian, and ceafes with the clofe of day; excepting fome 
plants, which continue it a fliort time after fun-fet. The 
quantity of dephlogiflicated air, in general, is greater in 
a clear day than when it is cloudy. It is alfo greater when 
the plants are more expofed to the fun than when they 
are fituated in fliady places. The damage done by plants 
in the night, is alfo more than counterbalanced by the 
benefit they afford in the dav-time. By a rough calcula¬ 
tion, the poifonous air, yielded by any plant during the 
whole night, could not amount to one hundredth part of 
•the dephlogiflicated air which the fame plant yielded in 
two hours time in a fair day. It does not appear, how¬ 
ever, that plants yield dephlogiflicated air by any kind of 
generation of that fluid, but only by filtrating the com¬ 
mon air, which all plants abforb through their pores; 
the phlogiflic part becoming part of their fubflance. Dry 
plants have little or no effect upon the air until they are 
moiflened. On all thefe experiments, however, it mufl 
be obferved, that they have fometimes failed in the hands 
of thofe whom we cannot but fuppofe very capable of 
trying them; as Mr. Scheele, Mr. Cavallo, and the Ab¬ 
be Fontana. 
After the publication of Dr. Ingenhoufz’s experiments, 
thofe of Sir Benjamin Thompfom appeared, in which the 
green matter fuppofed to be vegetable was fhewn to con- 
fifl of a number of animalculas. He obferved further, 
that feveral animal fubfiances, as well as vegetables, have 
a power of feparating dephlogillicated air from water 
when expofed to the light of the fun, and that fora very 
great length of time. Not that the fame quantity of wa¬ 
ter will always continue to furnifh air; but the fame ani¬ 
mal fubflance being taken out, wafhed, and again put in¬ 
to frefh water, feems to yield dephlogiflicated air, without 
any kind of limitation. 
Raw filk w'as the fubflance on which his experiments 
were firfl attempted; and he not only found that it was 
capable of yielding pure air in confiderable quantity when 
placed in the fame circumflances with the leaves of plants, 
but alfo that the light, no lefs required to produce dephlo¬ 
giflicated air from animal than vegetable fubfiances, was 
not, in either cafe, neceffarily that of the fun ; though in¬ 
deed the pure air was more fparingly fupplied, under the 
influence of an artificial light, than in the other cafe. In 
making the experiments, as it was found fomewhat trou- 
blefome to invert the globes in water, they were at lafl 
only kept in an inclined pofture on the table, the air col¬ 
lecting itfelf in the upper part of the belly. Having pro¬ 
vided himfelf with a number of globes, of different fizes, 
he proceeded in the following manner: 
Finding that raw filk, expofed to the aCtion of light, pro¬ 
duced fo great a quantity of air, he was induced to try 
,fome other fubfiances. Having, therefore, prepared fix 
globes of 4| inches in diameter, and filled them with fpring 
water, he introduced into each of them fifteen grains of 
one of the following fubfiances, viz. fheep’s-wool, eider¬ 
down, fur of a Ruffian hare, cotton-wool, lint, or the ra- 
velings of linen-yarn, and human-hair. The refults of 
thefe experiments were various, though all yielded more 
or lefs of pure air. The wool, even in the mofl favour¬ 
able circumflances, < never afforded more than one-third 
of the quantity which would have been yielded by filk. 
The eider-down began to furnifh air almoft immediately, 
and continued to do fo in quantities little lefs than had been 
furniflied by the filk, and nearly of the fame quality. T he 
fur of the hare produced more air than the wool, but lefs 
than the eider-down. The cotton yielded a confiderable 
quantity of air of better quality than any of the former. 
The ravelings of linen were very llow in furnifhing air, 
LOGY. 
and produced but a fmall quantity ; only two cubic inches 
being colleCled in the fpace of a fortnight. This fub¬ 
flance appeared to be the very reverfe of the hare’s fur; 
for the air, inflead of attaching and coliefling itfelf about 
tlie fubflance in large bubbles, fcarcely ever made its ap¬ 
pearance in fufficient quantity to raife it to the top of the 
wafer. The human-hair furnifhed llill lefs than the li¬ 
nen, and the produce was of inferior quality, though flill 
fuperior to the Common atmofphere. 
In order to difeover the comparative purity of air pro¬ 
duced from vegetables and from raw filk, a fmall quantity 
of air from the Hem of a pea-plant, which had four heal¬ 
thy leaves upon it, was proved with nitrous air, and found 
greatly inferior to that from raw filk, and feveral of the 
fubfiances already mentioned. An entire plant of houfe- 
wort, of a moderate lize, furnifhed only three-fourths of 
a cubic inch of air in feven hours, and that greatly infe¬ 
rior to common air; but the leaves alone afforded a much 
greater quantity, and of a quality greatly fuperior. 
In order to ascertain how much air would be yielded by 
expofure to the fun’s rays, a globe containing 296 inches, 
filled with frefh fpring water, and thirty grains of raw filk, 
was expofed to tire air for three days in the month of May, 
but for the mofl part cold and cloudy. Only nine inch.es 
and a half of air were produced ; but next day, by expo¬ 
fure to the fun from nine in the morning till five in the af¬ 
ternoon, 8-46 inches more were produced. Next day, the 
product of air was nine cubic inches, of a better quality; 
and the day following, fix inches flill fuperior, though ex¬ 
pofed only for three hours and a half; but the next day, 
it being cold and cloudy, only three-fourths of an inch of 
air were produced, and thefe manifeftly inferior to the 
foregoing. No more air could afterwards be procured, 
except one quarter of a cubic inch; fo that from 2C)f> 
inches of this w'ater, 33-96 of air v.ere obtained. 
In this experiment the air was every day removed, aqd 
its place fupplied with water : the follow ing was made to 
determine what alteration would take place on allowing 
the quantity of air produced to remain from firfl to laft; 
The globe being therefore filled again, and the filk well 
wafhed and replaced in it, the quantity of air produced 
amounted in four days to 30-1 cubic inches; and would 
probably have been flill more confiderable. 
On employing unwaflied raw filk, it was found, that 
feventeen grains in twenty cubic inches of water, produ¬ 
ced, for the firfl four days, air of a worfe quality than 
the atmofphere; but afterwards yielded near two inches 
of a fuperior quality. The quantity of this air was fupe¬ 
rior to that in other experiments, though its quality was 
fomewhat inferior. 
Thefe refults led to a trial of the cotton-like fubflance 
yielded bv the populus nigra. One hundred and twenty 
grains of this in 296 inches of water, during the firfl four 
days gave a very ineonfiderable quantity of air, and that 
in a phlogifiicated (late. On becoming Suddenly greeniffi, 
however, it yielded in fix days forty-four cubic inches and 
a quarter of purer air than had been before produced. 
Sufpetling that the quantity of pure air might depend 
on the comparative, quantity of fnrface, an hair of filk 
and one of poplar cotton were examined with a microf- 
cope, and found to be as 1000 to 346S. Whilfl thirty 
grains of the cotton prefented a furface of 6600 fquare 
inches, the like quantity of filk exhibited no more than 
476. Hence the produce of air from the two fubfiances 
was neither in proportion to their weights nor their fur- 
faces. It appeared alfo, that the quality of the air pro¬ 
duced at firfl was confiderably inferior to that yielded 
fome time afterwards. In order to afcertain the times at 
which air of the bell quality was produced, fee. feveral 
experiments were made. In fome of them, the water 
had acquired a fain- greenifh cad ; but the colour of that 
with the cotton was deepefl. On examining with a mi¬ 
cro fcope, it was found to coritain a great number of ani¬ 
malcules exceedingly fmall, and nearly of an oval figure; 
that with the filk contained them likewife, but not in fuc.b 
numbers; 
