AEROLOGY. 
100 
nitrous air. Marine acid poured on hepar fulphuris ex¬ 
tricates it however in vaft quantity. It is alfo produced 
naturally from putrefying matter. The frnell of the pure 
gas is intolerable; and it has a difagreeable e tie ft on iil- 
ver, lead, copper, See. which it renders quite black. It 
is fuddenly fatal to animal life, turns fyrup of violets 
green, and is inflammable, burning with a very light blue 
flame. It is decompofed by vitriolic and nitrous air, by 
dephlogifticated air, and by the contaft: with atmofpheri- 
cal air, in which cafe it depofrts a final 1 quantity of i'ul- 
phur; being indeed, as is luppofed by Mr. Bergman and 
Mr. Kirwan, no other than lulphur in an aerial form. 
Its fpccific gravity, compared with atmofpherical air, is 
as uo6to 1000. It combines readily with water, and 
gives the fmell to the fulphureous medicinal waters. Its 
great attraction for fome of the metals and their calces 
makes it the balls of fome kinds ot Sympathetic Ink. 
Of Atmofpherical Air. 
As the two component parts of our atmofphere, viz. 
dephlogifticated and phlogilticated air, have already been 
treated of, little remains to be determined, except the 
proportion in which they exilt in the common air. Mr. 
Scheele conftrufted an eudiometer, with which he exami¬ 
ned the goodnefs of the common air in Stockholm every 
day for a whole year, and found the diminution never to 
exceed -iJJ, nor to fall fliort of j; fo that upon a medium it 
may be eftimated at ff. During the months of January 
and February it was fff. The 23d of March it was 
though the cold increaled, and the barometer flood high¬ 
er. The 19th of April it was ^2-, though the barometer 
and thermometer did not vary, and lo flood til! the 21ft. 
In May and June it flood between and-^-j. The 30th 
of July it flood at From the 3d to the 15th of Sep¬ 
tember at fff. The 6th of Oftober at TJJ, during a high 
llorni; but after it flood between and till the 4th 
of November, when it fell to and continued between 
. and to the 20th, when it role to Vr- The 2ifl it 
and till the 8th of De- 
fell to 8, and flood between -fj 
cember, when it rofe to ^ ; and front thence to the 31 fl 
it flood between and Pfe . 
As the pure dephlogiflicated part of the atmofphere is 
confumed by phlogiflic procelles, fuch as that of ferment¬ 
ing brintflone and iron-filings, which formed the materi¬ 
als of this eudiometer, it mult be confidered as an exaft: 
tefl of the proportion of dephlogifticated air contained in 
the atmofphere. The fmall variation in the quantity 
fhews, that the procelles in nature which deftroy this ait- 
are nearly balanced by thofe which produce it; though it 
muft appear furprifing, that both thefe fluids, fo extreme¬ 
ly different, Ihould be produced at all feafons of the year 
in a proportion nearly equal; nor is it lefs furprifing that 
two fluids of unequal fpecific gravity fhordd remain incor¬ 
porated together without any tendency to feparate, .which 
it is certain they never do, either in the atmofphere itfelf, 
or when confined in velfels in any quantity whatever. 
As phlogilticated air is fomewhat lighter than dephlo¬ 
giflicated, it will hardly be luppofed, that the upper parts 
of the air contain a greater proportion of dephlogifticated 
air than thofe near the earth, which however is proved 
by the eudiometer. 
Of the Artificial ProduElion of Airs of different Kinds. 
Fixed Air, or Atrial Acid. The artificial methods of 
producing this are principally three, viz. by fermentation, 
. by heat, and by acids. 
By fermentation. When vegetable or animal fubftances, 
efpecially the former, are fermented, they yield a great 
quantity of fixed air. In breweries, on the furface of the 
fermenting liquor, there is always a ftratum of fixed air 
reaching as high as the edge of the vat. The cafe is the 
fame whatever fubflance it is that undergoes the vinous 
fermentation, though the quantity of fixed air produced 
is not the fame in all cafes, nor even in the fame fubflance 
at different times. From forty-two cubic inches of beer 
Tool 
ft I 0 ‘ an 
2V f ounce 
Ytii tV , meafure. 
fo J 
2 oz. meaiures. 
Dr. Hales obtained 639 cubic inches of air in thirteen 
days. From a quantity of fugar undergoing the vinous 
fermentation, Mr. Cavendifh obtained fo much fixed air, 
that out of 100 parts of the former fifty-feven appeared 
to have been volatilized and converted into fixed air. As 
the brifk'nefs and agreeable pungent acidulous tafte of all 
fermented liquors depends on the quantity of fixed air 
remaining in them, whenever they become vapid and flat, 
we are able to reftore their flavour by impregnating them 
again with fixed air, either naturally or artificially pro¬ 
duced. 
Dr. Prieftley made feveral experiments in order to de¬ 
termine the quantity of fixed air contained in feveral forts 
of wine, and found that 
’Madeira "J 
Port of fix years old 
i-J oz. Hock of five years 
meafure f Barrelled claret 
of 1 Tokay of 16 years 
I Champagne of 2 years | u 
^Bottled cyder 1 2 years J 8 
During the acetous fermentation alfo, liquors emit a 
vapour, great part of which is fixed air, though the na¬ 
ture of its other component parts has not yet been tho¬ 
roughly afeertairied. 
Fixed air is likewife produced, though in no great 
quantity, by putrefaction. In this cafe, however, a great 
part of the claflic fluid confifls of inflammable and phlo- 
giflicated air, and the fixed air itfelf feents to be inti¬ 
mately conneftcd with a putrid offenlive effluvium. The 
elaftic fluid produced by vegetables putrifiying in a mo¬ 
derate degree of heat, is almofl all fixed air. Thefe yield 
almolt all the permanently-elaftic fluid in a few days, but 
animal bodies continue to emit it for feveral weeks. 
By heat. In every combuflion, except that of lulphur 
or of metals, a quantity of fixed air is generated. Du¬ 
ring its extrication from atmofpherical air, the latter, is 
fuppofed to be confiderablv diminiflied; but Lavoifier and 
Scheele have now rendered that opinion doubtful. If 
charcoal be burned by a lens when contained in a glafs 
receiver inverted in water, after the apparatus is cooled, 
the water will have mounted a fmall way into the receiv¬ 
er. The diminution, however, is limited, and depends 
on feveral circumftances. Dr. Hales has obferved, that 
in equal receivers, the air fuffers a greater diminution by 
burning large candles than fmall ones; and likewife that, 
when equal candles are made life of, the diminution is 
greater in fmall than in large receivers. The caul’e of 
this phenomenon probably is, that the air contained in 
the receiver cannot all come into contaft: with the flame 
of the candle ; whence, as foon as the air which is neareft 
the flame becomes contaminated, the candle is extin- 
guiflied. This diminution has been ftated by different 
philofophers in different degrees. M. Lavoifier has ob¬ 
ferved, that by the combuflion of phofphorus, air may 
be diminiflied of about one-fifth or one-fixth. This ac¬ 
curate philofopher has alfo obferved, that the acid of 
phofphorus thus formed acquires the weight loll by the 
diminiflied air ; finding that about three inches of air were 
abforbed by every one grain of phofphorus, w hen the ex¬ 
periment was tried with a receiver inverted in water; bur, 
when in quickfilver, the abforption was conflantly between 
2% and 2^ inches for each grain. Mr. Cavallo often re¬ 
peated the experiment of burning phofphorus in a glals 
tube inverted in water, by applying the clofed part of the 
tube, wherein the phofphorus was contained, to a pretty 
ftrong fire, when he always obferved that the utmoft dimi¬ 
nution of the inclofed air effected by this means was full 
one-fifth. 
In thefe experiments of burning combuftible bodies in a 
quantity of air, and meafuring the diminution, we Ihould 
be aware of two caufes.of miftake, viz. the abforption of 
air by the coaly refiduum of the burned matter, which 
fometimes is very confiderable, or by the fluid in which 
the receiver is inverted, and the production of elaftic flu¬ 
id. 
