A C I 
but I believe much depends on the degree of heat to 
which the tube is fubjected. But having diftilled man- 
ganefe, which yielded of itfelf fome fixed air with com¬ 
mon fpiritof fait, I obtained dephlogifticated marine acid, 
and not a particle of fixed air; which fhews that this laft 
combined with the dephlogifticated balls, and formed the 
dephlogifticated acid.” 
Several other experiments are related by Mr. Kirwan; 
but the following, he is of opinion, fully confirms his hy- 
pothefis, and fubverts that of the antiphlogillians. “Six 
cubic inches of inflammable air were mixed with as much 
dephlogifticated marine air over lime-water. In about 
ten minutes after the greater part of the diminution had 
taken place, a white cloud appeared on the furface of the 
lime-water, and by agitation it became flill more turbid. 
As it was poffible that the manganefe might be mixed 
with calcareous earth, fome dephlogifticated marine air 
was extracted from another portion of it, and received on 
lime-water; but it was wholly abforbed, without forming 
the leaft cloud, though there was lime enough ; for, on 
adding aerated water, a cloud appeared.” 
The other acids particularly treated of by Mr. Kirwan 
are the phofphoric and faccharine. In his treatife on the 
former, he adopts the analylis of M. Lavoilier, changing 
only his acid principle of dephlogifticated for fixed air. 
From this it appears, that the phofphoric acid conllfts of 
a peculiar balis united to 2-265 of its weight of the acid 
principle; or, in other words, 100 grains of dry phofpho¬ 
ric acid contain about 69 of fixed air and 31 of its peculiar 
bafis : ioo grains of the phofphoric balis take up 226-5 of 
fixed air, or 32-9 of phlogillon when it becomes phof- 
phorus; and 100 grains of phofphorus contain 75-24^ 
balis and 24-76 of phlogillon.—The bafis of this acid is 
the only one that can be procured free, both from the 
phlogillon and the acidifying principle; it is called, though 
improperly, as it is not foluble in water, the glacial phof- 
phoric acid. M. Lavoifier and others are of opinion, that 
phofphorus is a Ample fubftance containing no phlogillon, 
and that the acid confiftsof the oxygenous principle united 
to it. 
With regard to the acid of fugar, Mr. Kirwan ob- 
ferves, that fugar itfelf is a compound of fixed air with a 
much larger proportion of inflammable air, and fome wa¬ 
ter, all condenfed to a degree of which we are ignorant, 
but retaining, upon the whole, much more fpecific heat 
than either oil or charcoal; though he ieems inclined to 
the hvpothefis of M. Morveau, that this fubftance has 
for its bafis a fine ethereal oil, to which a large proportion 
of condenfed inflammable air is fuperadded. The acid of 
fugar, then, according to him, conlifts of this peculiar 
bafis deprived of its fuperftuous phlogillon, and united to 
a great quantity of fixed air in a concrete Hate. He is al- 
fo of opinion, that it does not exift ready formed in the 
fugar, but is produced in the operations that fubftance 
undergoes : that it derives moll of its acid principle from 
the nitrous acid employed ; the nitrous bafis taking up the 
phlogillon, and the fixed air of the nitrous acid combining 
with the faccharine bafis. He contefts ftrongly an opinion 
of M. Lavoifier, that fugar is a fort of charco'al, which 
uniting with the oxygenous principle of the nitrous acid, 
decompofes it, fets loofe the nitrous air, and forms the 
faccharine acid ; and that, towards the end of the opera¬ 
tion, the faccharine acid itfelf is decompofed ; the confe- 
quence of which is the production of fixed air, w hich, ac¬ 
cording to him, is only the oxynenous principle combined 
with charcoal. Among other objections, Mr. Kirwan 
fays, “ If the acid of fugar be diddled, it is wholly con¬ 
verted into water, fixed inflammable air, and not a parti¬ 
cle of coal or dephlogifticated air is found in it. It is not 
therefore reafonable to look on either of them as its con- 
ftituent principles ; but, as fixed air alone can be extracted 
from all vegetable acids, it feems to be the true acidifia- 
ble principle.” 
Having given a view of the prefent opinions relative to 
the original formation of acids, it remains to treat a little 
3, 
A C I *]T) 
more particularly of each of the different kinds. They 
are divided into three different claffes, expreftive of their 
origin, viz. the Mineral, Vegetable, and Animal. The 
mineral acids are, thofe of vitriol, nitre, fea-falt, borax, 
amber, fiuor, arfenic, tungften, molybdena, &c. The 
vegetable are, thofe of vinegar, tartar, fugar, benzoin, 
apples, citrons, lemons, tamarinds, forrel, cork, &c. 
The animal acids are, the microcofmic or acid of urine, 
and that of bones, both of which are alfo called the pkoj- 
phoric, though this might be accounted a vegetable acid, 
as it is procured by diddling milliard and l'ome other ve¬ 
getables by a violent fire. Befides thefe, there are the 
acids of ants, wafps, bees, filk-worms, milk, &c. It 
has alfo been difeovered, that the human calculus is form¬ 
ed for the mod part of a peculiar acid, which has received 
the name of lithiafic acid. Laftly, as an acid diftinCt from 
all thefe, we may now add fixed air, by fome called thear- 
rial and by others the cretaceous acid : the latter appella-. 
tion it derives from creta, chalk, becaufe it is found in 
that fubftance in great quantity. See Aerology. 
The general properties of acids have already been enu¬ 
merated ; the mod remarkable of which is their attrac¬ 
tion for alkaline falts, earths, and metals. Though this 
is common to all, yet very confiderable differences areob- 
ferved among them in this refpedt, and on thofe differ¬ 
ences depend almoft all the phenomena of that part 
of Chemistry which treats of falts. As thefe pheno¬ 
mena are particularly confidered under that article, we 
fhall here only in general take notice, that the three acids, 
named the vitriolic, nitrous, and marine, are the ftrongeft of 
them all ; that is, if any other acid be united to an alkali, 
earth, or metal, the union will be broken by adding to 
that compound any of the three acids juft mentioned. 
Neither are thefe equal in power among themfelves j for 
the vitriolic is ftronger than the nitrous, and the nitrous 
ltronger than the marine. The rule, however, is liable 
to certain exceptions and variations, depending chiefly on 
the circumftances of heat or cold, moifture or drynefs, and 
particularly on the Hate of the marine acid with regard to 
its being in the form of an aqueous fluid or reduced to a 
dry vapour. In this laft cafe it feems ftronger than either 
the vitriolic or nitrous ; and even when in an aqueous 
date, both the nitrous and marine acids, when added.in 
great quantity, feem to opprefs and overwhelm the ftrong¬ 
er vitriolic acid, fo that they will partly expel it from art 
alkaline fait. This does not depend on the mere quanti¬ 
ty of acidity they poffefs : for the acetous acid may be 
concentrated to fitch a degree as to become ftronger in this 
relpect than fpirit of fait; yet it will always be inferior in 
point of real ftrength, when tried with an alkali in com¬ 
petition with the latter. The aerial acid is the weakeft 
ot all; and may be expelled not only by vinegar, but by 
the acid juices of fruits, tartar, and the acids of tungfteni 
and molybdena. 
Sortie acids have the property of refilling the fire, and 
melting into a kind of glafs, fuch as that of borax and 
phofphorus. This circumftance gives them an advantage 
over the ftronger acids, which are volatile; and thus the 
two juft mentioned, as well as thofe of arfenic and tung'.- 
Iten, will, in a very llrong heat, expel the acid of vitriol 
itfelf, though the latter will, in the cold, expel any one o£ 
them with great eafe. 
Both the vitriolic and nitrous acids have a very ftrong 
attraction for phlogillon ; and unite with certain oily and' 
inflammable matter fo vehemently as to occalion great 
heat, and lometimes even violent and unextinguilhable 
flame. This is particularly the cafe with the nitrous acid, 
or with a mixture of the two ; and indeed the nitrous acid, 
though weaker than the vitriolic, Ihewsitfelf in everyin- 
(lance to be far more active, and to perform all its opera¬ 
tions with valtly greater rapidity, than the other. All; 
thefe however fall under the articles Chemistry, Sec. 
We owe to Scheelc- not only the difcovery of the oxyge¬ 
nated muriatic acid, commonly called dephlogifticated ma¬ 
rine acid ; but alfo.that of the effects which it produces upon. 
the 
