O X A
OX A
( 189 )
licular defcriptioli of the ores of each metal,of their analyfis, and the methods purfued intheir reduction, fee the firft, fecond, and thirdfeblions, in the account of each metal.
OXALIC ACID. Sauerkleesatire. Germ.
This acid is found frequently but not abun-dantly native, in various combinations, and itis alfo produced by the mutual action of thenitric acid upon a vaft number of vegetable andanimal fubftances. It is found native in a fewacid vegetable juices, and in tolerable abundancein the exprefled juice of the sorrel plant (OxalisAcetofella. Linn.) naturally united with aquantity of potafh not fufficient for compleatfaturation, forming an acidulum which has longbeen prepared for culinary and medicinal pur-pofes in fome parts of Europe , and fold as theEJfcntial Salt of Sorrel , long before its real naturewas difcovered. This acid is found in fomefpecies of urinary calculi.
The oxalic acid is artificially prepared byboiling a fufficient quantity of nitric acid witha variety of vegetable and animal fubftances,fuch as fugar, mucilage, alcohol, filk, animaljelly, &c. &c. and many of the other vegetableacids (tire acetous exceptedJ are convertibleinto the oxalic by the aftion of the nitric acid.
The oxalic acid as artificially prepared, wasfirft difcovered by Bergman, who has given avery valuable eflay on the fubjedl. This emi-nent chemift prepared it by diftiliing nitric acidfrom fugar, and hence he termed it the Acid ofSugar. But as the acid of the native fait offorrel was foon after difcovered by Scheele toidentical with the acid of fugar, the term OxalicAcid has been more commonly adopted, and thecombinations of this acid with the various bafes,have been termed Oxa/ats.
This acid is prepared from fugar, very limplyand eafily by tlle following procefs : put a fmallquantity of white fugar into a tall glafs matrafs,with a narrow neck, add thereto fix times itsweight of concentrated nitrous or nitric acid,°f moderate ftrength, apply heat, and bring itgradually to boil, during which the fugar fpeed-jly diflblves in the acid, and then decompofes
with evolution of abundance of nitrous va-pour. Continue the boiling for about tenjrunutes, then fet the liquor by to cool, when» will depofit regular cryftals of oxalic acid.
apovatc the remaining liquor conficierably,3 ^ cooling another crop of cryftals may be
procured, and fometimes' a third. Rediffolve
all the cryftals in as much water as will takethem up when boiling, and by cooling flowlythe cryftals will again feparate in a more regularform, and freed from the adhering nitric acid.Dry thefe cryftals on blotting paper, and theyare the pure oxalic acid. A retort and receivermay be ufed for the procefs inftead of a mat-trafs, when it is an object to fave the fuperflu-ous nitrous acid. About 58 parts of oxalicacid may thus be obtained from 100 of fugar.
The oxalic acid when in a regular form,cryftallizes in four-fided prifms, the faces ofwhich are alternately broad and narrow, andterminating in dihedral fummits. Thefe cryf-t?.ls do not deliquefce, but by expofure to theair they fall into a white powder.
This acid has a very pungent, and when-diluted, a very grateful fournefs. The cryftalsdiflblve in their own weight of boiling water,and twice their weight of cold water. a Thefpecific gravity of a cold faturated folution isabout 1.06, This acid has all the commonproperties of acids, of changing vegetablecolours, and forming neutral falls with thealkaline, earthy, and many metallic bafes. Italfo forms acidula with all the alkalies, whenthe proportion of acid predominates.
This acid, like all the other vegetable acids,is decompofed, and its acid properties deftroyedby heat, more or lefs com pleat! y in proportionto the degree of heat. If heated in a retortwith a gentle fire the water of the cryftals firftcomes over, amounting to about of. thewhole, and the acid fufes. On encreafingthe fire, the acid grows brown, and part of it isfublimed as a white faline cruft, but the greaterpart is refolved into carbonic acid, and carbu-retted hydrogen, which come over in largequantity, having a pungent empyreumatic fmell.The refidue in the retort entirely burns away inthe open air, without leaving any afb.
Alcohol when boiling readily d ill dives fome-what more than half its weight of oxalic acid.On cooling, a fmall portion is depofited in fmall-fcaly cryftals, but the greater part remains infolution. The alcoholic folution when heatedyields a portion pf alcohol holding fome of the.acid diffolved, and alfo a very, fmall quantity of.an imperfefft ether.
Sulphuric ether diffolves oxalic acid, thoughwith difficulty..
Sulphuric acid heated upon the- oxalic black-ens it j and the two fubftances are mutually,decompofed in part.
The nitrous or nitric acid readily diffalvea
* Bergman, on the Acid of Sugar.