3 jo C H £ M 
ammoniac and potafh, the nitrat of barytes is poured. 
A precipitate is formed of oxalat of barytes, and the 
nitric acid retains the alkalis. The barytic oxalat, when 
well wafhed, is decompofed by the addition of fulplniric 
acid, which combines with'the barytes, and remains in- 
i'oluble at the bottom. The fluid being decanted, is to 
be afl'ayed by the addition of a fmall quantity of barytic 
oxalat, dilfolved in Toiling water, to feparate the por¬ 
tion of fulphuric acid which may be contained in it; and, 
when no more precipitate is affoi-ded, the liquid, which 
contains the pure oxalic acid, may be decanted. This 
being duly evaporated, affords, by cooling, the cryftal- 
lized fait in quadilateral prifins, whole faces are alternate¬ 
ly broad and narrow', and are terminated by dihedral 
fummits. Thefe cryffals often have the form of fquare 
or rhomboidal plates. 
To procure this acid in laboratories, it is extrafted 
-■from fugar, by combining the oxygen of nitric acid with 
one of its conllituent principles. For this purpofe, pour 
eight parts of nitric acid over one part of fugar ; put the 
whole into a retort, which place on a fand-bath ; adapt 
a receiver, and give a gentle heat to help the aftion of 
the acid. Some nitrous gas is difengaged ; and, when 
the decompoftion is finifhed, continue the diftillation 
in a find-heat till the refidue be fufficiently concentrated; 
then, by cooling, cryffals will be formed in the liquor, 
which are to be feparated by decantation; fpread them 
on blotting paper to dry ; after which diflblve them afrefli 
in diftiiled water, and evaporate for more cryffals. 
This acid is always concrete; it has a very penetrating 
four tafte ; feven grains give to two pounds of w’ater a 
fenflble degree of acidity; it reddens all blue colours : 
one grain of the fait gives to 3600 grains of water the 
property of reddening paper tinged with turnfole. The 
concrete oxalic acid, expofed to a mild heat, becomes 
dry, and covered with a white crult; foon afterwards it 
is reduced to powder, with the lofs of three tenths of its 
weight. By diffillation in a retort with a ftronger heat, 
though ftili moderate, it liquefies, becomes brown, boils 
tip, affords an acidulous phlegm, fublimes in part with¬ 
out alteration, at the fame time that a mixed gas, con¬ 
fiding of carbonic acid ami hydrogen gas, is difengaged. 
If a very ffrong heat be applied, more gas, lefs of con¬ 
crete fubiimed acid, and more acidulous phlegm which 
is not cryltallizable, are afforded : there remains at the 
bottom of the retort, a grey or brown mafs, forming -J 5 
cf the acid employed. If laid upon ignited charcoal in 
the air, it exhales in a very acrid white fume, which 
Irrongiy irritates the lungs, and leaves only a white refidue 
without any coaly matter. Such is the refult of the de- 
compofition of the oxalic acid by heat, as obferved by 
Bergman. 
The concrete oxalic acid, expofed to a moiff air, re¬ 
mains deliquefcent, but it rather becomes dry in a dry 
atmoiphere : cold water difl'olves half its weight. When 
the cryffals of this acid are thrown into cold water, they 
produce a flight noife, which indicates a fudden breaking 
of the particles. The fpecific gravity of this cold folution 
is 1-0593, according to Morveau. If the water of folu¬ 
tion be evaporated, no acid vapour aril'es, even by ebul¬ 
lition. Boiling water difl'olves its own weight of this 
concrete acid fait. One half is precipitated in cryffals 
by cooling. This acid combines with all the faline bales, 
forming oxalats. 
The affinity of this acid for lime is fuch, thaj it takes 
it from every other; and Bergman propofes it as a teft 
to dilcover the prefence and quantity of lime in mineral 
waters. At any rate, this peculiar property is fufficient 
to diftinguifh it from all other acids. 
The third genus of the vegetable clafs, confiffs of acids 
by the aftion of fire. Pyro , from the Greek Trup, fire, 
is prefixed to the name of each. There are only three at 
prefent well known, the pyro-tartarous, pyro-mucous, 
and pyro-lignous, acids. 
I S T R Y. 
PYRO-TARTAROUS acid. 
Fill a glafs retort about half way with the pulverifed 
acidule of potafh 5 adapt a tubulated receiver, commu¬ 
nicating by a tube with a jar in the pneumatic apparatus. 
By graduating the fire, an empyreumatic acid liquor, 
mixed with oil, is obtained; fepai'ate the two produfts 
by means of a funnel, and the acid liquor is what we 
call pyro-tartarous acid. This acid is not quite pure; 
it always contains fome oil, which it were to be wifhed 
could be feparated ; but the rectification, or fecond dif¬ 
tillation, of this acid, which has been recommended by 
a great number of authors, exhibits a very great difficul¬ 
ty, according to the academicians of Dijon, namely, that 
the rapid elevation of the liquid always burft the veffels, 
in fpite of every care they took to moderate the heat, 
and leave room for the vapours. They attribute this ele¬ 
vation to the gas produced by the decompofition of the 
acid, and comprefl'ed by the oil, againft the preffure of 
which it-prevails at laft by its great dilatation. However, 
this rectification may be difpenfed with ; and the acid, 
feparated from the oil by means of the funnel, is fuffici¬ 
ently pure to exhibit all its diltinftive characters. 
The pyro-tartarous acid has an empyreumatic fmell 
and tafte; it does not redden violets, but it does turnfole 
and blue pap'er; it difengages the carbonic acid from its 
bafis, with a ffrongeffervefcence. With earths and alkalis 
it forms falts, which are very different from thofe con- 
llituted by the tartarous acid. Chemiits, before they 
arrived at the knowledge that hydrogen, carbon, and 
oxygen, appear to be the true principles of all the vege¬ 
table acids, which differ from each other only in the pro¬ 
portions, had adopted opinions very remote from truth, 
concerning the acid obtained by diffillation from tartar. 
Vennelaffinnedjthatitwastheacidofnitre. Monnet.upon 
more politive experiments, imagined this acid to be the 
muriatic acid, difguifed by oil and mucilage. But though 
Scheele found a fmall portion of muriatic acid in tartar, 
yet the cubic form of the neutral lklt, produced by ad¬ 
ding the pyro-tartarous acid to foda, and the precipitation: 
of the nitrat of mercury, are not at prefent fufficient for 
chemifts to afeertain the identity. 
PYRO-MUCOUS ACID. 
All faccharine, gummy, and farinaceous, matters, pro¬ 
duce this acid by diftillation. Put the fugar into a retort, 
(it fhould be a very large one, becaufe the matter fwells 
up,) and adapt a receiver large enough to condenfe the 
vapours. When the heat firft begins to aft, a large quan¬ 
tity of carbonic acid and hydrogen gas are difengaged.' 
A brown liquor is found in the receiver, of which the 
greater part is a weak acid, reddening blue paper, and 
coloured with a portion of oil, a fpongeous coal remain¬ 
ing in the retort. Guyton obtained the acid lefs coloured 
by a fecond diffillation. 
Schrickel obtained, from fixteen ounces of fugar, fix 
drachms of phlegm, paifing in white vapours, and con- 
denfed in oily ffreams, of a penetrating fmell of horfe- 
raddifh, or roafted bitter almonds, of an acid and bitter 
tafte, and of a yellowifh-red colour. He reftified it from 
clay; the acid pafled clear with a mild fmell and a fourer 
tafte. The acid, thus purified, did 110c cryftalbze; but, 
when expofed to cold, the aqueous part froze, and the 
portion which remained liquid was much more concen¬ 
trated. Morveau obferved, in preparing the pyro-mucous 
acid by the diftillation. of fugar, that the bottom of the 
retort was corroded. He does not attribute this corrofion 
to the acid, which exhibits not that property when rec¬ 
tified, or when left a long time in the glafs, but to the 
aftion and adherence of the carbure of iron, which exifts 
in the relidual charcoal left by the fugar, and which he 
had heated very ftrongiy. Tnis acid cannot be concen¬ 
trated by the volatilization of the water which is united 
to it, becaute it is itielf as volatile as that fluid. It is 
this acid which exifts in melalfes, and according to Mor- 
veau. 
