AERO 
tity about one-third, or half of the water. The air will 
then pafs through the tube into the inverted bottle, , as in- 
other indances. 
In order to obferve the property this elaftic fluid pof- 
fedes of diminifhing the bulk of common air, let a glafs 
tube, elofed at oneend, and about nineinches long, be filled 
with, and inverted in, water ; then take an half-ounce vial, 
and, plunging it under the inverted tube, let all the air en¬ 
ter and go to the top of it, the water fubfiding according¬ 
ly. Let a mark be made, by llicking a bit of wax on the 
tube, juft oppofite to the furface of the water, which will 
mark how much of the tube is filled by that given meafure 
of air. Repeat this four or five times, marking the tube 
as the water defcends each time. Now, if three meafures 
of common air be conveyed into this tube, when filled with 
water and inverted, they will fill a fpace of it as far as the 
third mark. The fame thing will happen if three mea- 
fures-of nitrous inftead of common air be put into it; but 
if two meafures of common air and one meafure of nitrous 
air, or one meafure of the former and two of the latter, be 
fucceffively introduced, they will fill a fpace much ftiorter 
than the third mark. The moment theie two kinds of air 
come in contact, a reddifh cloud is perceived, which foon 
vanifties; and the water, which at firft nearly reached the 
third mark, rifes gradually into the tube, and becomes fta- 
tionary after about two or three minutes ; which ftiews 
that the diminution is eftefted gradually. See Eudio¬ 
meter. 
To procure DcphlogiJUcated Air. The eafieft way of pro¬ 
curing this air is to put fome red-lead into the apparatus, 
together with fome Itrong vitriolic acid, but without any 
water. Let the red-lead fill about a quarter of the bottle, 
and the vitriolic acid be about the fame quantity ; then 
apply the bent tube to the bottle, and proceed as above. 
Without heat, however, this mixture- will not give any 
dephlogifticated air, or but an inconfiderable quantity ; 
for which reafon the flame of a wax-taper nmftbe applied 
tinder the bottom of the bottle. In this manner the red- 
lead will yield a quantity of elaftic fluid, the greateft part 
of it dephlogifticated air, but not the whole, a portion of 
fixed air being generated at the fame time. In order to 
feparate the fixed air, the inverted bottle, as the air is emit¬ 
ted from the red-lead, mult be fhaken in the bafon for im¬ 
pregnating water with fixed air ; by w hich means the wa¬ 
ter will abforb the whole quantity of fixed air, and leave 
the dephlogifticated air in a pureftate. 
Animals will live much longer in this kind of air than 
in an equal quantity of common air; whence it is fuppofed 
that the breathing of it mull contribute to longevity much 
more than the common atmofphere. Dr. Prieftley howe¬ 
ver conjectures, that dephlogifticated air might perhaps 
wear out the fyftein much fooner than common air, in the 
fame manner as it confumes fuel much falter than common 
air. In Cavallo’s Treatife on Air, it is laid that “a man 
makes in general about fifteen infpirations in a minute, and 
takes in about thirty cubic inches of aerial fluid. But the 
air which has been once infpired is not thereby much in¬ 
jured, and it may be refpired again and again; fo that, 
upon a very moderate calculation, and as appears from ex¬ 
periments often repeated, we may fafely aflert, that a per- 
fon can breathe 400 cubic inches of good ordinary atmof- 
pheric air, at leaft thirty times, without any inconvenience, 
i. e. it would ferve for two minutes; after which the air, 
though much depraved, is ftill in a Bate of being breath¬ 
ed, but then it would occalion fome uaeafmefs. Now, 
fuppofmg the dephlogifticated air employed to be four 
times more pure than common air, 400 cubic inches of de¬ 
phlogifticated air would ferve for at leaft 120 refpirations, 
or eight minutes. 
“ But fuppofing that thirty inches of common air are 
tompletely phlogifticated by a Angle infpiration, and 
changed for fuch as is quite frelh, which indeed is the cafe 
in common refpiration, then 450 cubic inches of common 
air will be requifite for one minute’s refpiration, and 27,000 
for one hour ; and, as dephlogifticated air is fuppofed to 
LOGY, 1.63. 
be four times as good, the fame quantity of it will ferve 
for four hours. Indeed, if we could depend on the affec¬ 
tions of Mr. Fontana, that by adding lime-water to ab¬ 
forb the fixed air produced by refpiration, an animal can 
live thirty times as long as without it, no doubt a much 
fmaller quantity would ferve.” 
But this cannot be true ; becaufe, though the fixed air 
ftiould be abforbed as foon as produced, the remaining 
quantity would ftill be contaminated by phlogifton. Nay, 
Dir. Prieftley, who repeated Fontana’s experiments, af- 
ferts, that animals will not live longer in dephlogifticated 
air when in contact with lime-water, than when no lime- 
water is ufed. Flow a difference fo enormous can take 
place, between philofophers in other refpefts fo accurate, 
we cannot determine. It is plain, however, that if 27,000 
inches of common air are neceflary for a perfon in one 
hour, the fame quantity of dephlogifticated air cannot be 
breathed longer than four hours, nor even fo long with any 
real advantage. Mr. Cavallo indeed allows only 12,000. 
inches for four hours ; but, though this might fuftain life, 
it would not be fuperior to the atmofphere, and perhaps 
much lefs falubrious. 
A very ready method of procuring dephlogifticated air 
in large quantity, is by means of nitre ; which mull be. 
put into a retort or other, veil’d, fo as to fill half or nearly 
three quarters of its belly; then a bent glafs tube is luted 
to the neck of the earthen veftef, in fuch a manner as not; 
to let any elaftic fluid efcape. The bed lute or cement 
for this is a mixture of whiting and drying oil. The retort 
being put into the furnace, mult be furrounded with 
lighted charcoal, which is to be renewed as it waftes, and 
the belly of the retort mult be kept quite red, or rather, 
white-hot, for three hours at leaft. The air is then to be 
received into large glafs jars, as ufual. The retorts made, 
of thofe metals which are ufually employed for this pur- 
pofe, viz. iron and copper, phlogifticate the air as foon as 
produced. The expence at prelent neceflary in London 
for the production of 12,000 cubic inches of dephlogifti¬ 
cated air (viz. the price of one pound of nitre, of an earth¬ 
en retort or other velfel, and of charcoal), amounts to about 
4s. or 4s. 6d'. 
Another method of preparing dephlogifticated air is by 
blowing common air through melted nitre. In this pro- 
cefs the phlogifton of the atmofphere is confumed, by de¬ 
tonating with the acid 01 the nitre, and therefore fifties 
much more pure than before. This method appears at 
firft much eaiier than the former; but, as it is impoflible 
to mix atmofpheric air fo exa,filly with the melted nitre that 
their particles may come uniformly in contact with each 
other,, it is plain the former method mult be preferable ; 
not to mention that the nitre will be apt to concrete into 
lumps by the cold blaft. 
To procure Vitriolic Acid Air. Some concentrated vitrio¬ 
lic acid mull be put into the bottle, along with fome fub- 
llance capable of furnifliing phlogifton. Olive-oil anfwers 
very well. The acid lhould be about three or four times 
as much as the oil, and both together fhould fill about 
one-third or half of the bottle. The elaftic fluid may 
then be produced by applying the flame of. a wax taper, 
as directed above. 
To procure Marine Acid Air. Put fome common fait in¬ 
to the bottle, fo as to fill about one-fourth part of it, and 
upon this pour a ftnall quantity of concentrated vitriolic 
acid; then apply the bent tube, and pals the air through 
quickfilver into the receiver. 
To procure Nitrous Acid Air. This may be obtained from 
heated nitrous acid, the vapour of which acquires a per¬ 
manent eiafticity. The great difficulty, however, is to 
find a fluid capable of confining this acid air during the 
procefs, as its being abforbed by water is one of the pro¬ 
perties by which it differs from nitrous air. It ails upon, 
quickfilver, and alfo upon oils; and hence its examination 
Cannot but be very iinperfeiL When water has abforbed 
a good quantity of this elaftic fluid, it acquires, the uro- 
perties of nitrous acid; and, when heated, it yields a large 
quantity 
