7 8 A C I 
a mixture of putrid air and common air, or putrid and 
dephlogifticatedair; but, if the putrid air be palled through 
lime-water, it is never generated ; and that it is rarely 
produced by the expofure of quick-lime orfixed alkalies to 
thefe airs. The reafon that alkalies, though aerated, are 
not fo proper, is, that they do not combine with phlogif¬ 
ticated air as calcareous earths do. Mr. Cavendifh, in¬ 
deed, produced nitrous acid without any apparent mix¬ 
ture of fixed air; but the atom of it necefiary for the for¬ 
mation of the fmall quantity of nitrous acid he produced 
(about one-third of a grain), might well be contained in 
the phlogifticated air he employed, or perhaps formed in 
the operation.” 
We (hall now notice i'ome experiments made by Mr. 
Watt, in order to determine whether the dephlogifticated 
air produced from nitre really proceeds from a decompo- 
fition of the acid, or what quantity of the latter is re¬ 
quired to conftitute a determinate quantity of the former. 
To afcertai.n this, 240 grains df mercury were put into a 
glafs retort with 480 grains of diluted dephlogifticated ni¬ 
trous acid, which was the quantity necefiary to diffolve 
the whole of the mercury ; and, as foon as the common 
air was expelled, a proper veffel was applied to receive the 
air produced in the operation. Sixteen ounce-meafures 
of nitrous air came over during the folution, and on chang¬ 
ing the receiver, a quantity of dilute, but highly phlo¬ 
gifticated nitrous acid, was obtained. The air receiver 
being again applied, four ounce-meafures of ftrong and 
pure nitrous air were obtained, which, by the dephlo- 
gifticated air that arofe immediately after, were reduced 
to half an ounce-meafure. The production of dephlo¬ 
gifticatedair continued very rapid, the mercury being all 
the while revived, until the operation was ended by the 
diftillation or fublimation of the w hole of the mercury. 
Two hundred and eighteen grains of the metal were ob¬ 
tained in its running form, and 22 remained in the form 
of an orange-coloured fublimate in the upper part of the 
retort. The 16 ounce-meafures of nitrous air, firft ob¬ 
tained, were then converted into nitrous acid by the gra¬ 
dual admiftion of common air, and then added to the wa¬ 
ter in the bafon in which the receiver had been inverted ; 
the whole quantity being about two quarts, and very acid 
to the tafte, fparkling at the fame time with nitrous air. 
To determine the quantity of acid thus recovered, as well 
as that which remained in the fublimate, a folution of al¬ 
kali of tartar was made ; and by experiment it was found 
that 120 grains of the acid, originally employed in dif- 
folving the mercury, faturated 352 grains of this folution; 
the orange-coloured fublimate and all the acid liquor re¬ 
covered being faturated by 1395 grains of the fame. 
Hence it appears, by the rule of proportion, that, out of 
480 grains of nitrous acid originally employed, only five 
were loft ; “ a fmaller quantity (as Mr. Watt juftly ob- 
ferves) than what might reafonably be fuppofed to be loft 
in the procefs by the extreme volatility of the nitrous 
acid.” His concluiion therefore is, that “the nitrous a- 
cid does not enter into the compofition of dephlogifticated 
air : it feems only to ferve to abforb phlogifton from the 
watery part of the mercurial nitre.” 
This experiment was repeated with cubic nitre, and 
only 30 ounce-meafures of air diftilled from an ounce of 
the mineral alkali exactly faturated with nitrous acid. 
The water through which the air paffed was acid, and the 
refiduum in the retort alkaline ; but, on mixing the two 
together, the folution was found to be exaCtly neutral by 
every poftible teft. 
Not fatisfied with thefe experiments, Mr. Watt engaged 
in others which appeared to be ftill more decilive, but to 
which, as well as the foregoing, Mr. Kirwan replies—. 
“ This opinion is expofed to infurmountable difficulties. 
For, in the firft place, nitre affords dephlogifticated air at 
the rate of 146-125 cubic inches for every 100 grains of 
nitre, which, by the proper allowances for phlogifticated 
air, fhould weigh 46-77 grains; but then dephlogifticated 
air is only one of the conftituent parts of water, for it 
A C I 
contains 13 per cent, of inflammable air, that is to fay, 87 
grains of dephlogifticated air : to form too grains of wa¬ 
ter requires an addition of 13 grains of inflammable air; 
confequently 46-77 grains of dephlogifticated air require 
nearly 7 of inflammable air, and would then form 53-77 
grains of water, which exceeds half the weight of the ni¬ 
tre; a quantity of water, as Mr. Watt owns, certainly in- 
admiffible. Mr. Watt found, that the water, over which 
the air proceeding from the decompoiition of 960 grains 
of nitre had been received, contained only the acid be¬ 
longing to 120 grains of nitre ; and even this fmall quan¬ 
tity he inferred only from my experiments. But my ex¬ 
periments are totally inapplicable in this cafe ; for I ufed 
only the dephlogifticated nitrous acid : and alkalis are fa- 
turable by a much fmaller quantity of phlogifticated than of 
dephlogifticated acids, as is evident in the cafe of the dc. 
phlogifticated marine acid, as Stahl long ago obferved ; for 
he fays, that the volatile acid of fulphur faturates ten 
times as much alkali as the fixed. Mr. Bergman and Mr. 
Scheele obferve, that melted nitre is ftill neutral, though 
it be phlogifticated ; therefore it is air, and not water, 
which it wants. Accordingly Dr. Prieftley found it to in¬ 
jure common air by attracting its dephlogifticated part : 
but, if it be kept in fuiion for fome time, it lofes its acid, 
and becomes alkaline ; and the air it receives muft furely 
be deemed rather to recompofe the acid than to form wa¬ 
ter; of whofe formation, in the temperature of the at- 
mofphere, we have no fort of proof. On the contrary, 
the impofiibility of accounting for the lofs of acid in 
this cafe is an evident proof of the fallacy of that hypo- 
thefis.—By M. Lavoifier’s analyfis, 100 grains of nitre 
contain 57 of cauftic alkali ; by Mr. Bergman’s, 49 ; by 
Mr. Wenzel’s, 52; by Mr. Wiegleb’s, 46^; by mine, 
63: the mean of all which is, 53^; which leaves 46-5 for 
acid and water, which is very nearly the weight of the ait- 
expelled. The different quantity of acid aftigned by dif¬ 
ferent perfons to nitre, is in part owing to its degree of 
phlogiftication in nitre. I believe at prefent, that 100 
grains of nitre contain 34 of acid and about 12 of water, in¬ 
cluding the water in the acid and that of cryftallization.” 
Mr. Kirwan next proceeds to confider the compofition of 
the other acids.—The marine acid, according to him, con- 
lifts of a peculiar bails united to phlogifton, and a certain 
quantity of fixed air; to both of which the bafts feems to 
have a ftrong affinity. 
M. Lavoifier, and other philofophers, who deny the 
exiftence of phlogifton, are of opinion, that the common 
marine acid conftfts of a peculiar bafts united to a fmall 
proportion of pure air, or oxygenous principle, and the 
dephlogifticated marine acid differs from it only by con¬ 
taining an excefs of this principle.—This opinion they are 
chiefly induced to maintain, becaufe the acid in its dephlo¬ 
gifticated ftate is procured by diftilling common marine 
acid from manganefe ; and the manganefe, if diftilled by 
itfelf, before the acid is diftilled from it, affords dephlo¬ 
gifticated air ; but, after the acid is diftilled from it, it 
yields none.—“ This experiment, however, (fays Mr. 
Kirwan,) proves no more but that the manganefe contains- 
fome air which is dephlogifticated during the calcination'. 
And that this air is fixed air, appears from the following 
confiderations : The black calx of manganefe almoft al¬ 
ways gives out fixed air at firft, before any dephlogifti¬ 
cated air appears ; whence it is natural to think, that the 
dephlogifticated air proceeds from the dephlogiftication of 
the fixed. And hence, if it be diftilled with filings of 
iron, or in a gun-barrel, it fcarcely gives out any other than 
fixed air ; if at any time it gives out dephlogifticated air 
with little or no mixture of fixed air, this is owing to a 
very perfect deplogiftication of the calx, and to its con¬ 
taining very little moifture. Thus Dr. Prieftley, having 
paffed the fteamof boiling water through manganefe heat¬ 
ed in an earthern tube, obtained a very, large quantity of 
fixed air, and fcarcely any other ; though, on repeating this 
experiment with manganefe well freed from calcareous 
earth* I obtained a large portion of dephlogifticated air; 
