The oxalic acid is mostly prepared in Switzerland and Germany from the expressed juice of sorrel, from which it cristallizes by being left long at rest; in this state it is partly saturated with potash, forming a true acidulous oxalat of potash, or salt with excess of acid. To obtain it pure, it must be formed artificially by oxygenating sugar, which seems to be the true oxalic radical. Upon one part of sugar pour six or eight parts of nitric acid, and apply a gentle heat; a considerable effervescence takes place, and a great quantity of nitrous gas is disengaged; the nitric acid is decomposed, and its oxygen unites to the sugar: By allowing the liquor to stand at rest, cristals of pure oxalic acid are formed, which must be dried upon blotting paper, to separate any remaining portions of nitric acid; and, to ensure the purity of the acid, dissolve the cristals in distilled water, and cristallize them afresh.
| Bases. | Neutral salts. | Names of the resulting neutral salts according to the old nomenclature. |
| Barytes | Acetite of barytes | Unknown to the ancients. Discovered by Mr de Morveau, who calls it barotic acéte. |
| Potash | —— potash | Secret terra foliata tartari of Muller. Arcanum tartari of Basil Valentin and Paracelsus. Purgative magistery of tartar of Schroëder. Essential salt of wine of Zwelfer. Regenerated tartar of Tachenius. Diuretic salt of Sylvius and Wilson. |
| Soda | —— soda | Foliated earth with base of mineral alkali. Mineral or crystallisable foliated earth. Mineral acetous salt. |
| Lime | —— lime | Salt of chalk, coral, or crabs eyes; mentioned by Hartman. |
| Magnesia | —— magnesia | First mentioned by Mr Wenzel. |
| Ammoniac | —— ammoniac | Spiritus Mindereri. Ammoniacal acetous salt. |
| Oxyd of zinc | —— zinc | Known to Glauber, Schwedemberg, Respour, Pott, de Lassone, and Wenzel, but not named. |
| —— manganese | —— manganese | Unknown to the ancients. |
| —— iron | —— iron | Martial vinegar. Described by Monnet, Wenzel, and the Duke d'Ayen. |
| —— lead | —— lead | Sugar, vinegar, and salt of lead or Saturn. |
| —— tin | —— tin | Known to Lemery, Margraff, Monnet, Weslendorf, and Wenzel, but not named. |
| —— cobalt | —— cobalt | Sympathetic ink of Mr Cadet. |
| —— copper | —— copper | Verdigris, crystals of verditer, verditer, distilled verdigris, crystals of Venus or of copper. |
| —— nickel | —— nickel | Unknown to the ancients. |
| —— arsenic | —— arsenic | Arsenico-acetous fuming liquor, liquid phosphorus of Mr Cadet. |
| —— bismuth | —— bismuth | Sugar of bismuth of Mr Geoffroi. Known to Gellert, Pott, Weslendorf, Bergman, and de Morveau. |
| —— mercury | —— mercury | Mercurial foliated earth, Keyser's famous antivenereal remedy. Mentioned by Gebaver in 1748; known to Helot, Margraff, Baumé, Bergman, and de Morveau. |
| —— antimony | —— antimony | Unknown. |
| —— silver | —— silver | Described by Margraff, Monnet, and Wenzel; unknown to the ancients. |
| —— gold | —— gold | Little known, mentioned by Schroëder and Juncker. |
| —— platina | —— platina | Unknown. |
| Argill | —— argill | According to Mr Wenzel, vinegar dissolves only a very small proportion of argill. |
From the liquor remaining after the first cristallization of the oxalic acid we may obtain malic acid by refrigeration: This acid is more oxygenated than the oxalic; and, by a further oxygenation, the sugar is convertible into acetous acid, or vinegar.
The oxalic acid, combined with a small quantity of soda or potash, has the property, like the tartarous acid, of entering into a number of combinations without suffering decomposition: These combinations form triple salts, or neutral salts with double bases, which ought to have proper names. The salt of sorrel, which is potash having oxalic acid combined in excess, is named acidulous oxalat of potash in our new nomenclature.
The acid procured from sorrel has been known to chemists for more than a century, being mentioned by Mr Duclos in the Memoirs of the Academy for 1688, and was pretty accurately described by Boerhaave; but Mr Scheele first showed that it contained potash, and demonstrated its identity with the acid formed by the oxygenation of sugar.
Sect. XXXIII.—Observations upon Acetous Acid, and its Combinations.
This acid is composed of charcoal and hydrogen united together, and brought to the state of an acid by the addition of oxygen; it is consequently formed by the same elements with the tartarous oxalic, citric, malic acids, and others, but the elements exist in different proportions in each of these; and it would appear that the acetous acid is in a higher state of oxygenation than these other acids. I have some reason to believe that the acetous radical contains a small portion of azote; and, as this element is not contained in the radicals of any vegetable acid except the tartarous, this circumstance is one of the causes of difference. The acetous acid, or vinegar, is produced by exposing wine to a gentle heat, with the addition of some ferment: This is usually the ley, or mother, which has separated from other vinegar during fermentation, or some similar matter. The spiritous part of the wine, which consists of charcoal and hydrogen, is oxygenated, and converted into vinegar: This operation can only take place with free access of air, and is always attended by a diminution of the air employed in consequence of the absorption of oxygen; wherefore, it ought always to be carried on in vessels only half filled with the vinous liquor submitted to the acetous fermentation. The acid formed during this process is very volatile, is mixed with a large proportion of water, and with many foreign substances; and, to obtain it pure, it is distilled in stone or glass vessels by a gentle fire. The acid which passes over in distillation is somewhat changed by the process, and is not exactly of the same nature with what remains in the alembic, but seems less oxygenated: This circumstance has not been formerly observed by chemists.
Distillation is not sufficient for depriving this acid of all its unnecessary water; and, for this purpose, the best way is by exposing it to a degree of cold from 4° to 6° below the freezing point, from 19° to 23° of Fahrenheit; by this means the aqueous part becomes frozen, and leaves the acid in a liquid state, and considerably concentrated. In the usual temperature of the air, this acid can only exist in the gasseous form, and can only be retained by combination with a large proportion of water. There are other chemical processes for obtaining the acetous acid, which consist in oxygenating the tartarous, oxalic, or malic acids, by means of nitric acid; but there is reason to believe the proportions of the elements of the radical are changed during this process. Mr Hassenfratz is at present engaged in repeating the experiments by which these conversions are said to be produced.
The combinations of acetous acid with the various salifiable bases are very readily formed; but most of the resulting neutral salts are not cristallizable, whereas those produced by the tartarous and oxalic acids are, in general, hardly soluble. Tartarite and oxalat of lime are not soluble in any sensible degree: The malats are a medium between the oxalats and acetites, with respect to solubility, and the malic acid is in the middle degree of saturation between the oxalic and acetous acids. With this, as with all the acids, the metals require to be oxydated previous to solution.