146 Aero 
face of the vefTel. The inflammable air, ifluing from the 
orifice of the (mail tube, was fet on fire previous to the 
inverfion of the matrafs, and the mouth of the latter im- 
merfed in the water; on which that fluid foon began to 
rife, and continued to do fo till l’even-eighths of the veil'd 
were full. In cafes of flow combuftion, where common 
air is diminifhed and phlogifticated, the dephlogifticated 
kind was found to bealmol! entirely deflroyed. 
The purity of dephlogifticated air is afcertained by its 
degree of diminution with nitrous air; which is to be cou¬ 
riered as a phlogiftic procefs. Very great differences are 
perceived in this refpeft; and, according to the quantity 
of diminution, the air is laid to be two, three, or four, 
times better than common air. It is not yet accurately 
determined how far this proportionable purity extends. 
Dr. Prieftley mentions fome extracted from red lead five 
times as pure as common air. Another quantity produced 
from a folution of mercury in nitrous acid, was fo pure, 
that one meafure of it mixed with two of nitrous air, 
which had been obtained in the firftpart of the fame procefs, 
occupied only 0-03 of a meafure. On the whole, he is 
inclined to think, that, were it poflible to make both the 
dephlogifticated and nitrous air in the greateft purity, and 
then to mix them in fome exaff proportion, the aerial form 
of them both would be deftroyed, the whole quantity 
feeming to difappear, as in the mixture of alkaline and 
acid air. Yet, notwithftanding its great purity, the belt 
dephlogifticated air is capable of being contaminated 'by 
fome of the procelfes which affect the atmofphere. Dr. 
Prieftley found ^ confirmed by a quantity of clean dry 
nails, which had remained in it nine months, though w ith¬ 
out being rufted. The ettebts of combuftion have already 
been mentioned, as producing a great quantity of pure 
fixed air ; but putrefaction and animal refpiration proba¬ 
bly contaminate it as in atmofpheric air. Mr. Cavallo 
informs us, that, when an animal is confined in dephlo¬ 
gifticated air till it dies, that air is not fo bad but that it 
will (till be capable of diminution by nitrous air; which 
feems to fhew, that dephlogifticated air is fomewhat dif¬ 
ferent from pure common air ; or that common air is ori¬ 
ginally different from dephlogifticated air lowered by the 
addition of phlogirton. It is certainly very remarkable ; 
and fometimes a quantity of dephlogifticated air, after 
having been breathed by an animal till it died, will appear 
by the nitrous teft to be even better than common air. 
When the experiment is performed over lime-water (to 
abforb the fixed air produced in refpiration), the diminu¬ 
tion by a mixture of nitrous air is lefs than it would other- 
wife be'; but itis ftill diminifhed much more than common 
air after an animal has died in it; which feems to inti¬ 
mate, that the death of the animal in dephlogifticated air 
is principally owing to the fixed air formed by the ail of 
refpiration. 
Dephlogifticated air is much inferior to that of the com¬ 
mon atmofphere in fupporting vegetable life. This has 
been afcertained by the experiments of Dr. Prieftley, Mr. 
Fontana, Mr. Scheele, Dr. Ingenhotifz, &c. Dr. Prieft¬ 
ley took three fprigs of mint, and introduced them into 
different jars of dephlogifticated air, common air, and air 
which had been phlogifticated with nitrous air feveral 
months before. The plant in phlogifticated air grew much 
better than that in common air; while that in dephlogifti¬ 
cated air had a (ickly appearance. It was found, however, 
that, though the plant in phlogifticated air had grow n fo 
well, the air was not fenfibly improved by it, whilft the 
dephlogifticated air was injured by the plant.- 
Compofition of Dephlogificated Air .—When Dr. Prieftley 
firft difcovered the exiftence of this fluid, lie imagined it 
was compofedof the nitrous acid and earth, with as much 
phlogifton as was neceflary to its elafticity; and that the 
common atmofphere had as much more as was required to 
bring it into the mean condition in which we find it. His 
experiments however were oppofed by others made by La- 
voilier; who infilled, that, when a folution of mercury was 
carefully diftilled, the metal was obtained in full quanti¬ 
le O G Y. 
tv, or with fcarcely any lofs, notwithftanding the dephloj. 
gillicated air produced. Having put two ounces and one 
drachm of mercury into red precipitate, and afterwards- 
revived it, a very tew grains of the metal were loft. Mr. 
Fontana repeated the experiment often, lofing lefs than a 
grain. The velfel he ufed had a neck of about two feet 
long: and he particularly remarks, that, in order, to fuc- 
eeed in this experiment, the fire fhould be managed with 
very great dexterity; for, if that be too ftrong, part of the 
precipitate will be volatilized. 
Thefe experiments were oppofed by others made by Dr. 
Prieftley ; but ftill the quantity of mercury loft, or rather 
the proportion of it to that of the metal employed,, was al¬ 
ways various, and the difference not very fmall; whence 
Mr. Cavallo and others,.with, great appearance of reafon, 
conclude, that the true reafon of any perceptible lofs was 
the ftrong heat made ufe of in the diftillation, and confe- 
quently that there is no reafon to fuppofe that any earth 
exifts in dephlogifticated air. The next queftion-.was,. 
Whether any of the nitrous acid exilted in-dephlogiftica¬ 
ted air ? That it contains none-in a proper ftate of acidity,, 
is indeed evident from many decilive experiments ; but an 
idea was naturally entertained, that in the formation of de¬ 
phlogifticated air the nitrous acid was decompofed, and 
part of it entered into the compofition of the aerial fluid. 
This gave rife to the theories of Mr. Lavoifier and Mr. 
Kirwan, which are noticed under the article Acid; as 
alfo the experiments of Mr. Watt, which tended to fhew 
that no nitrous acid was deftroyed in the.coinpofition of de¬ 
phlogifticated air. 
On calcining metals in dephlogifticated air, very.lingular, 
phenomena are obferved, w hich feem to throw great light 
upon the compofition of this fluid. “ One of the 1110ft Am¬ 
ple of all phlogiftic precedes (fays Dr. Prieftley) is that in 
w hich, metals are melted in dephlogifticated air. I-there- 
fore began with this, with a view to afeertain whether any 
water be produced when the air is made to difappear in it. 
Accordingly, into a glafs-velfel,. containing feven ounce- 
meafures of pretty pure dephlogifticated air-, I introduced 
a quantity of thin iron-turnings-. I then fired the iron by 
means of a burning lens, and prefently reduced the feven 
ounce-meafures to 0-65 of a meafure; but 1 found no more.- 
wafer after this procefs than I imagined it had not been 
poflible for me to exclude, as it bore no proportion to the 
air which had difappeared. Examining the refiduum of- 
the air, I found one-fifth of it to be fixed air; and, when I 
tried the purity of that which remained by the teft of ni¬ 
trous air, it did not appear that any phlogifticated air had r 
been produced in the procefs : for though it was more im¬ 
pure than I fuppofe the air with which I began the expe¬ 
riment mu ft have been, it was not more fo than the phlo- 
gifticated air of the feven ounce-meafures which had not 
been affebted by the procefs, and which mult have been- 
contained in the refiduum, would neceflarily make it. In 
this cafe, one meafure of this refiduum, and two of nitrous 
air, occupied the fpace of 0-32 of amealure. In another,, 
ten ounce-meafures of dephlogifticated air were reduced to 
o"8 of a meafure; and by walking in lime-water to o - 3& 
of a meafure. In another experiment, 7 \ ounce-meafures. 
of dephlogifticated air were reduced to half an ounce- 
meafure, of which one-fifth was fixed air, and the refiduum 
was quite as pure as the air with which I began the expe¬ 
riment ; the teft with nitrous air, in the proportions above- 
mentioned, giving 0'4 in both cafes.” 
From thefe experiments the dobtor was led to the dis¬ 
covery, that the dephlogifticated air had .actually been im¬ 
bibed by the melted iron, in the fame manner as inflamma¬ 
ble air had been imbibed by the melted calces of metals in 
his former experiments. In the firft inftance, about twelve 
ounce-meafures of dephlogifticated air had difappeared, 
and the iron had gained fix grains in weight. On repeat¬ 
ing the experiment, other quantities of iron, treated in 
the fame manner, gained an addition of weight, always 
very nearly that of the air which had difappeared. 
Dr. Prieftley now proceeded to try the eftebt of fufing 
iron 
