AERO 
numbers: however, in all cafes in which the water acqui¬ 
red a greenith hue, they never failed to exift, fo as to ren¬ 
der it probable, that, from their prefence alone, the co¬ 
lour of the water in the firft inftance univerfally arofe. 
To determine a point which appeared by no means deci¬ 
ded, viz. what lhare the fubftances employed had in pro¬ 
ducing air, and whether any other which prefented a large 
furface, and attracted air from water, would not do as 
well, the experiment was repeated with a quantity of fpun 
glafs, and the refult was, that, the globe being expofed in 
the fun,'air-bubbles began almoft inftantly to make their 
appearance on the furface, and in four hours 0-77 of a 
cubic inch of air was procured; after which, not a Angle 
globule more was produced, though the globe was expo- 
fed for a whole week in funfhine weather. Hence it ap¬ 
pears that fomething more than mere furface was wanted 
to produce dephlogifticated air from water by means of 
Hie fun’s light. 
To determine the quantity and quality of air produced 
by means of the heat and light of the fun from water 
alone, a large glafs, containing 455 cubic inches, was fill¬ 
ed with frefli fpring water, inverted, and expofed for 
twenty-eight days. Another jar was alfo filled with wa¬ 
ter from a pond in which many aquatic plants were grow¬ 
ing, and expofed in the fame way. The latter yielded air 
in pretty large quantities on the third day, and continued 
to do fo till the fourteenth ; the former little or none till 
the fourteenth, when it began to emit air, and continued 
to do fo till the twenty-fecond. On removing the air pro¬ 
duced, that from the fpring water was fourteen inches in 
quantity, and 138 in quality (taking the quality of atmof- 
pheric air at 100); but, from the pond water, thirty-one 
and a half in quantity, and 232 in quality. The colour of 
the water remaining unchanged, the thicknefs of the glafs 
veflel was thought an objeftion. The experiment there¬ 
fore was repeated in a thin conical jar containing 344 inch¬ 
es, and expofed twenty-one days to the fun. Little air 
was furnifhed till the feventh day, when, a fine flimy fedi- 
ment of green matter beginning to be formed, air was 
furnifhed in pretty large quantities till the eighteenth, when 
it entirely ceafed. The whole amounted to forty cubic 
inches, and the quality 213. 
The opinion of Dr. Ingenhoufz, that the dephlogiftica- 
ted air was elaborated in the veffels of the plant, appeared 
exceedingly doubtful to the ingenious author of thefe ex¬ 
periments : for, befides that many other fubftances, in 
which no elaboration takes place, caufe the water to yield 
dephlogifticated air as well as plants, and even in much 
greater quantities, and of a more eminent quality; the 
circumftances of the leaves of a vegetable, which, accuf- 
tomed to grow in air, are feparated from its ftenr and con¬ 
fined in water, are fo unnatural, that it is difficult to con¬ 
ceive they can perform the fame functions in fuch different 
lituations. 
Frefh healthy leaves furnifh air only for a fliort time, 
and, after a day or two, change colour and ceafe to yield 
any. This has been conceived to arife from the death of 
the plant: and from hence it has been inferred, with fome 
degree of platthbility, not only that the leaves actually 
retain their vegetative powers for fome time after being fe¬ 
parated from their ftock; but that it was in confequence 
of the exertion of thofe powers, that the air yielded in 
the experiment was produced. But though the leaves, 
expofed in water to the aftion of light, actually do ceafe 
to furnifh air after a certain time, yet they regain this pow¬ 
er after a ffiort interval, when they furnifh (or rather 
caufe the water to furnifh) more and better air than at 
firit; which can hardly be accounted for upon the fuppo- 
iition that the air is elaborated in the veffels of the plant. 
A confirmation of this doftrine has refulted from various 
experiments; and thus we fee, that nature is provided 
with abundant means of fupplying that pure part of the 
atmofphere which is fubject to fuch continual wafte. No 
doubt the light of the fun produces vital air from water 
Vol. I. No. 10. 
LOGY. i 4s 
as well as from vegetables, and even the waters of the 
ocean contribute towards this falutary purpofe. 
As dephlogifticated air may poffibly anfwer a valuable 
purpofe in medicine, a cheap method of procuring it is 
fuggefted by Mr. Cavallo, who propofes to diftil it from 
nitre with a ftrong heat; but the experiments already re¬ 
lated point out an eafier method. 
Properties of Dephlogijhcated Air. This kind of air pof- 
feffes fome of, though not all, the properties of common 
air. Thofe in which it excels, are the fupport of flame 
and of animal life. It is equally elaftic, or rather more 
fo than common air ; as it likewife exceeds it a little in fpe- 
cific gravity, the proportion betwixt it and common air 
being that of 160 to 152. In dephlogifticated air, the 
flame of a candle not only grows larger, but becomes ex¬ 
ceedingly bright; and burns with a crackling noife, as if 
the air contained fome combuftible matter, at the fame 
time that the wax or tallow waftes furpriiingly faft. The 
heat of the flame is in proportion to its light. If a blad¬ 
der full of dephlogifticated air be pricked with a pin, the 
ftream of air will augment the heat of a candle to fuch a 
degree, that if any fmall bits of metal be placed on a 
piece of charcoal, and held in the apex-of the flame, 
they will almoft inftantly be melted. 
On mixing dephlogifticated and inflammable- air to¬ 
gether, an explofion takes place as on mixing common and 
inflammable air, but with much greater violence. If an 
ounce vial, which for this purpofe iliould be very ftrong, 
be filled with a little more than one-third of dephlogifti¬ 
cated, and the reft inflammable, air, and the flame of a 
candle prefented to its mouth, it will explode nearly as 
loud as a fmall piftol. All phlogillic precedes are promo¬ 
ted much better by dephlogifticated than common air. 
Dr. Prieftley put a quantity of pyrophorus into a fmall 
jar, and threw in dephlogifticated air. It always occa- 
fioned a vehement accenfion, like the flaffiing of gunpow¬ 
der, and the air was greatly diminiihed. 
It has been, almoft throughout all ages, believed, that 
combuftion in every inftance diminiihed common air, or 
reduced it to a fmalier volume : but the late experiments 
of M. Lavoilier have (hewn, that this is a miftake; and 
that in ordinary precedes, attended with the production of 
fixed and phlogifticated air, the quantity of vapour pro¬ 
duced is equivalent to that abforbed, or otherwife'made to 
difappear, during the operation. With dephlogifticated air 
the cafe is very different. M. Lavoifier having introdu¬ 
ced a burning candle into a glafs jar filled with very pure 
air obtained from calcined mercury, a great heat took 
place; which at firft expelled a fmall quantity of the air 5 
but afterwards, when the candle was extinguifhed, it was 
found that two-thirds of the bulk of air employed had 
been converted into fixed air, or a quantity of this kind of 
air equivalent to the former had been produced. The re¬ 
mainder, after taking up the fixed air by cauftic alkali, 
was ftill as pure as before. In the common precedes, he 
obferves, that not more than one-tenth of tire air em¬ 
ployed is converted into fixed air. In this experiment, 
the fuperior gravity of fixed air, and the confequent con- 
denfation of the other, mult undoubtedly have produced 
fome diminution in the volume of air, though M. Lavoi¬ 
fier does not take notice of it. In other cafes, however, 
the diminution i.s much more perceptible. Mr. Scheele 
having introduced a piece of phofphorus into feven ounce- 
meafures of this kind of air, flopped tire mouth of the 
bottle, and fet fire to the phofphorus within: the vial 
broke in pieces, as foon as the flame was extinguifhed, 
by the prelfure of the external air. A ftronger vial being 
ufed, and opened afterwards under water, the fluid ralli¬ 
ed into it in fuch a manner as almoft to fill it entirely. 
This extraordinary diminution was alfo demonftrated by 
filling a matrafs with dephlogifticated air, and inverting 
it over a vial containing an eft'ervefeing mixture of vitrio¬ 
lic acid and iron-filings plunged into a veflel of hot water, 
and furnifhed with a Sender tube reaching above the fur- 
P p face 
