When combined with ammonia this acid becomes a valuable re-agent, by the property of separating iron from its solutions, and not operating upon other metals.

Experiment 2. Pour a little of this succinate of ammonia to a solution of sulphate of iron, and a succinate of the metal will be precipitated. It may be calculated that every 100 grains of the precipitate contain 68 grains of iron.

SECTION XXIII.

OF MOROXYLIC ACID.

Experiment 1. If the saline exudation, which incrusts the bark of the white mulberry tree, be dissolved in water, and precipitated by means of acetate of lead, the precipitate afterwards digested with sulphuric acid, moroxylic acid will be disengaged.

Rationale. The saline exudation consists of the acid in question united with lime; the addition of acetate of lead, therefore, by double affinity, takes the moroxylic acid from the lime, forming a precipitate of moroxylate of lead, whilst the lime unites with the acetic acid. Sulphuric acid then decomposes the precipitate; sulphate of lead is formed, and moroxylic acid is disengaged.

Remark. This acid was discovered by Klaproth.. It crystallizes in needles. It is soluble in water and in alcohol. It is volatile, and may be sublimed.

SECTION XXIV.

OF CAMPHORIC ACID.

Experiment 1. Put into a retort one part of camphor and eight of nitric acid, distil the mixture, and repeat it three times on the same residue with a like quantity of acid; after the last distillation is accomplished, crystals will be found in the retort, which are camphoric acid; re-dissolve them in boiling water, and suffer the fluid to crystallize.

Rationale. The nitric acid is decomposed; a part of its oxygen goes to acidify the camphor, whilst the other part is disengaged in union with azote in the form of nitrous gas.

Remark. Camphoric acid exists in the form of white parallelopipedes which effloresce in the air. Its state is acid, slightly, and somewhat bitter. It strongly reddens vegetable blues. It is very volatile; it is sparingly cold; soluble in water, more soluble in alcohol, in sulphuric, nitric, and muriatic acid, and in volatile and fat oils. It is fusible, and sublimes by heat.

This acid was first accurately described by La Grange.

SECTION XXV.

OF OXALIC ACID.

Experiment 1. Put one part of white sugar into a retort, and pour over it four parts of nitric acid, of about 1.567 specific gravity, adapt a receiver, and make the solution boil. When the fluid in the retort acquires a brown colour, add three parts of acid more, and continue the boiling till it again becomes brown; then add two parts more of acid, and continue the heat till the

red fume almost disappears. Having done this, suffer the mixture to crystallize. After having removed the obtained crystallized acid, the residue may again be treated in a similar manner as before, until no more crystals are obtained. It may then be purified by dissolving it in water, and re-crystallizing it repeatedly.

Rationale. The sugar is converted into an acid by the nitric, which, by decomposition, imparts oxygen to it, forming therewith the oxalic or saccharinc acid.

Remark. Cxalic acid is always concrete; its crystals are colourless quadrilateral prisms, having their sides alternately broad and narrow, and terminating in two-sided summits, of a very acid taste. It is particularly distinguished by its strong attraction to lime, which is superior to that of any other acid. It is not altered on exposure to air. It acts on most of the metals. Exposed to heat it becomes decomposed into carbonic acid, and carburetted hydrogen gas. It contains more oxygen than any other vegetable acid. Oxalic acid is soluble in its own weight of water at 212, and in about two parts of water at 65°. It reddens vegetable blues readily. Boiling alcohol dissolves somewhat more than half its weight. It is composed of 64 oxygen, 32 carbon, and 4 hydrogen. This acid exists ready formed in many vegetable substances, as in the salt of sorrel.

Sal-acetosellæ, or the salt of sorrel of commerce, has usually been imported from Switzerland and the neighbouring countries, where it is prepared in large quantities from the juice of sorrel.

The oxalic radical appears to exist still more abundantly in insipid matters. Berthollet has obtained from wool more than half its weight of oxalic acid.

Two of its most striking applications may be exhibited in the following manner:

Experiment 2. Pour a few drops of the solution of oxalic acid into a neutral solution of muriate of lime, and an abundant precipitate of insoluble oxalate of lime will immediately appear. If there be any excess of muriatic acid in the solution, the lime will be re-dis

solved. Hence the superiority of oxalate of ammonia, to simple oxalic acid, as a test.

Experiment 3. Spot a piece of linen with common ink, and, when the spots are dry, rub them over with a solution of super oxalate of potash. This will dissolve the iron in the ink, and the stains will consequently disappear.

SECTION XXVI.

OF MELLITIC ACID.

Experiment 1. If the stone called mellite or honey stone be pulverised and boiled in seventy-two times its weight of water, the solution then filtered and evaporated, crystals of mellitic acid will be formed.

Remark. This acid was discovered by Klaproth. Few of its properties have been investigated.

SECTION XXVII.

OF TARTARIC ACID.

Experiment 1. To obtain tartaric acid dissolve thirty-two parts of acidulous tartrate of potash in water, and throw chalk into it gradually till it is completely saturated, a precipitate will be formed; decant the fluid, and put the precipitate into a matrass, pour over it nine parts of sulphuric acid and five of water; digest the whole for six hours, taking care to stir it from time to time; the tartaric acid will then remain free, and may be separated, by means of cold water, from the sulphate of lime which has been formed, and crystallized by suffering it to evaporate slowly.

Remark. To ascertain whether the tartaric acid contains sulphuric acid, let fall into it a few drops of acetite of lead: if the precipitate, which is formed, be entirely soluble in acetous acid, the fluid contains no sulphuric acid; if it is not soluble, sulphuric acid is present: to free it from this fluid it must again be digested over another quantity of the tartrate of lime.

Rationale. The carbonate of lime is decomposed; the tartaric acid in excess in the supertartrate, unites with the lime into a tartrate of lime. Sulphuric acid then decomposes the precipitate; sulphate of lime is formed, and tartaric acid is disengaged.

Remark. Tartaric acid exists in the juices of many vegetables, generally combined with lime.

It appears in the form of tabular crystals. Its specific gravity is 1.5962. Its taste is exceedingly sour. It is permanent in the air. It readily dissolves in water. The solution is not decomposed by evaporation nor on exposure to air, unless very diluted. It takes lime from the nitric, muriatic, phosphoric, and acetous acids. It has a strong tendency to unite to potash. In one proportion it forms a soluble salt (tartrate of potash) but when the acid is in excess it forms a salt of difficult solubility (acidulous tartrate of potash.) It is on this account that the presence of tartaric acid in any solution may easily be detected. It is decomposable by heat. It may be changed into oxalic acid, by the repeated use of nitric acid. Tartaric acid is composed, according to Fourcroy, of 10.5 oxygen, 19.0 carbon, 15.5 hydrogen.