AEROLOGY, 
* 5 * 
vitriolic acid ; but 1 learned from Mr. Methrie, that this 
is peculiar to the vitriolic acid, the remains of which, 
•diffufed through the inflammable air procured by it, he 
conjectures, may actually decompofe the fixed air produ¬ 
ced in the procefs. For, as I have hinted before, when 
the inflammable air is produced from iron by means of 
fpirit of fait, there is a very perceivable quantity of fixed 
air when it is united with dephlogifticated air. When I 
decompofed thefe two kinds of air in equal quantities, they 
were reduced to about o - 5 of a meafure, and of this not 
more than about one-fortieth part was fixed air. This 
experiment ought, however, to be added to the other 
proofs of fixed air being produced by the union of de¬ 
phlogifticated air and phlogifton. 
“ The laft inftance which I (hall mention of the gene¬ 
ration of fixed air from phlogifton and dephlogifticated 
air, is of a much more ftriking nature than any that I 
have yet recited. Having made what I call charcoal of 
copper , by parting the vapour of fpirit of wine over copper that 
was red-hot, I heated a piece of it in different kinds of 
air. In common air, obferving neither increafe nor de- 
creafe in the quantity, I concluded, perhaps too haftily, 
that no change was made in it; for, when I repeated the 
experiment in deplogifticated air, the charcoal burned 
very intenfely; and, when part of it was confirmed, (which, 
like common charcoal in the fame procefs, was done with¬ 
out leaving any fenfible refiduum,) I found that no heat 
which I could apply afterwards had any farther effeft on 
what was left of the charcoal. Concluding, therefore, 
that fome change mud be made in the quality of the air, 
I examined it, and found about nine-tenths to be the pu- 
reft fixed air; and the refiduum was fuch as would have 
been made by feparating the abfolutely-pure part of the 
dephlogifticated air, leaving all the impurities behind. 
Having afcertained this fa£l, I repeated the experiment, 
weighing the piece of charcoal very carefully before and 
after the procefs ; and then found, that by the lofs of one 
grain of charcoal, I-reduced four ounce-meafures of de¬ 
phlogifticated air till one-ninth only remained unabforb- 
ed by water ; and again, with the lofs of a grain and a half 
of the charcoal, 1 reduced fix meafures and a half of de¬ 
phlogifticated air till five meafures and a half were pure 
fixed air. In this procefs there was a diminution of bulk 
after the experiment, as might have been expected from 
the change of the air into one of a heavier kind, by means 
of a fubftance or principle that could not add much to the 
weight of it. In one of the experiments, 4-3 ounce-mea¬ 
fures of dephlogifticated air were reduced about one-thir¬ 
tieth part of the whole; and, in this cafe, when the fixed 
air was feparated by water, there was a refiduum of 0-75 
of a meafure of the ftandard of i - o, whereas the dephlo¬ 
gifticated air, before the experiment, had been of the 
ftandard of o - 2. 
“ That dephlogifticated air aftUally enters into the com- 
pofition of the fixed air, in this experiment, is evident 
from the weight of the latter, which far exceeds that of 
the charcoal difperfed in the procefs. For, in this, laft 
experiment, the weight of the fixed air produced was 
4-95 grains. Confequently, fuppofing the charcoal to be 
wholly phlogifton, as it is very nearly fo, fixed air may be 
faid to conlift of 3-45 parts of dephlogifticated air, and 
i'; of phlogifton; fo that the dephlogifticated air is more 
than three times the proportion of phlogifton in it. I muft 
not conclude, however, without obferving, that, in one 
experiment, I never failed to produce fixed air; though 
it is not eafy to fee how one of its fuppofed elements, viz. 
dephlogifticated air, could enter into it. This is by heat¬ 
ing iron in vitriolic acid air. In one of thefe experiments, 
four ounce-meafures of the vitriolic acid air were reduced 
to 0-65 of an ounce-meafure; and of the quantity loft 
three meafures and a half were fixed air abforbed by lime- 
water, and the remainder weakly inflammable.” 
Pure fixed air is remarkably altered by the eleftric 
fpark. Dr. Prieftley, having taken the eleftric fpark for 
about two hours in a fmali quantity of fixed air, found 
that one-fourth of it remained immi-fcible with water; 
though, before it, only one-twentieth part had remained 
unabforbed. The infide of the tube had become very 
black; which, in fimilar experiments with vitriolic acid 
air, he had obferved to arife from the adhefionof a fmali 
quantity of mercury fuperfaturated with phlogifton. Pur- 
fuing this experiment, by taking the eledlric fpark three 
hours in a fmali quantity of fixed air, he obferved that it 
was firft increafed, and then diminifhed about one-eighth 
of the whole ; the infide of the tube being very black on 
the upper part, and below the mercury very yellow, for 
the fpace of one-fourth of an inch all round the tube; 
but this fpace had been above the mercury in the begin¬ 
ning of the operation. . One third of the air remained un¬ 
abforbed by water; but fo impure, that the ftandard of 
it was i-8, or almoft completely phlogifticated. Varying 
the procefs, by uiing water impregnated with fixed air in- 
ftead of mercury, the quantity of air was much augment¬ 
ed by that which came from the water; but thus the far 
greater part of it was incapable of being abforbed by 
lime-water; and, on this occalion he obferved, that water 
impregnated with fixed air is a much worfe conductor of 
electricity than the fame fluid impregnated with mineral 
acids. On (till varying the circumftances of the experi¬ 
ment, by ufing common water inftead of that which had 
abforbed fixed air, he found that the quality of the refi¬ 
duum was evidently better than that of the original fix¬ 
ed air. 1 
In order to difcover whether the heat or light of the 
electric (park were the circumftances which effected the 
change, the doCtor threw a ftrong light, by means of a 
lens, for fome hours, on a quantity of pounded glafs con¬ 
fined in fome fixed air; but thefe and other trials proved 
unfatisfaCtory, though the quantity of air was increafed 
after the operation. By heating iron, however, in fixed 
air, part of it was evidently converted into phlogifticated 
air. On heating turnings of malleable iron for fome time 
in fixed air, one-tenth part of it was rendered immifcible 
with water; and, on repeating the procefs with the re¬ 
mainder, there was a refiduum of one-fourth of the whole. 
There was alfo a fmali addition to the quantity of air af¬ 
ter the firft part of the procefs, but none after the fecond ; 
nor could he, after a third and fourth procefs, render 
more than one-fourth immifcible with water. In two ex¬ 
periments, the refiduum was inflammable, and burned 
with a blue flame. 
Witli regard to the quantity of fixed air which may be 
expelled from different fubftances, Dr. Prieftley obferves, 
that from feven ounces of whiting, the pureft calcareous 
fubftance we are acquainted with, he expelled by heat 630 
ounce-meafures of air; by which means the whiting was 
reduced to four ounces. One-third of this was fomewhat 
phlogifticated, the ftandard being 1-36 and 1*38. Repeat¬ 
ing the experiment, he obtained 440 ounce'-meafures of 
air from fix ounces of whiting; about half of which was 
fixed air, and the remainder of the ftandard of 1-4. On 
moiftening fome calcined whiting with water impregnated 
with vitriolic acid air, he obtained ninety ounce-meafures; 
of w'hich the firft portions were three-fourths fixed air, 
and the ftandard of the refiduum 1-5; the latter had lefts 
fixed air, and the ftandard of the refiduum was 1 -44. 
The whiting was rendered black and hard, but became 
foft and white with fpirit of fait. Three ounces and a 
quarter of lime fallen in the air yielded 373 ounce-mea¬ 
fures; of which about one-fifth was fixed air, and tire 
ftandard of the refiduum 1-4. Four ounces of white lead 
had yielded 240 meafures of air when the retort melted. 
The refiduum of the firft procefs was one-third, the ftand¬ 
ard 1*36; and of the laft the ftandard was 1-28, that with 
the common atmofphere being 1 ‘23. Two. ounces and 
three-quarters of w'ood-aflies yielded, in a. very ftrong 
heat, 430 ounce-meafures of air; of the firft portion of 
ivhich one-tenth, of the fecond one-third, and of the 
third one-half, was fixed air. The ftandard of the refi¬ 
duum of the firft portion was r6j and of the fecond 1-7. 
