This acid ie also distributed throughout the animal kingdom, being found in the mucous mem brane of the impregnated uterus, in blood, as a characteristie conetituent of the mulberry calculus, frequently in urine, and in the mucus of the gall-bladder of man, the ox, the dog, and the pike, as well ae in the liquor allantadis of the cow and iu the secretions of the caterpillar. In guano, too, it is found in combination with ammonia.
Even in the mineral kingdom this acid is not unknown ; three varieties of oxalate of lime have been named respectively Whewellite, Thierschite, aud Conistenite. Thicrschito was (lb.covured by Liebig as a grey, warty incrustation on the marble of the Athenian Parthenon, and is considered to have been formed by tho action of some plaut ou the marble. Grey found the conistonite to con sist of Oxalic acid .. 28.02 Magnesia and soda .. . 82 99'04 — Rarely, the acid occurs as a ferrous salt iu lignite beds, especially at Koloseruk, Bohemia, which, analysed by Rammeleherg, shows:— Oxalic acid .. .. 42.40 Protoxidc of iron .. 41.13 16'47 100.00 — MArturAcrrnma. 1. Prom Plants.—The extraction of oxalic acid from vegetable growths origi nated in Germany, and was carried on in Swabia. Only two plants appear to have been used—the wood sorrel, containing, according to Savary, 0'255 per cent. of hinoxalate of potash, and the first to bo employed, and the common sorrel, yielding by Bannaeh's analysis 0.764 per oent. of the salt. The large percentage contained in the latter plant led to its being cultivated for the express purpose of producing the binoralate of potash, the plant being sown in March and reaped in June. The leaves were reduced to e. pulpy condition in large niortars made of wood, when it was transferred to other vessels, and there treated with water. Allowed to stand for five or six days, the li.guid was removed, and the solid residue was pressed and again treated with water. All the solutions thus obtained were mixed together and run into wooden cisterns for purification, having been carefully filtered from the undissolved mass. A small quantity of pure whiteclay, added while the liquor was kept constantly stirred, effected its purification and chuifieation, after the liquid had been allowed to stand for twenty-four hours, that the sediment might completely fall to the bottom. Tee clear liquid was decanted iuto copper pans, and then evaporated till a pellicle or thin saline film com menced to appear on the surface, when it was run into coolers made of glazed stoneware, and then permitted to crystallize. A crop of crystals of binoxalate of potash was thus procured, and these were again dissolved and re-crystallized in order to remove all possible traces of colouring matters from the salt.
2. From Guano.—Though tbe extraetion of oxalic acid from gnano is not now in practical opera tion in this country, under certain conditions and in certain localities it may be profitably con ducted ; and we shall therefore notice the main features of the process.
It is essential to divide guano into two classes in their relation to this manufacture—(1) those in which the products of avine urine are intact and in a perfect state ; and (2) those in which chemical changes have produced various substances not originally present in the urine of birds, the latter being by far the more common. The class to which any sample of guano belongs may be easily ascer
tained by treating it with cold water, when the solution formed will give an acid reaction (like fresh urine) if it be of the former kind, but an alkaline reaction if it be referable to the latter species.
The treatment to which the former kind of guano is subjected is as follows. The mineral must first be reduced to a fine powder, and then be steeped and well washed in cold water, to remove the soluble urine salts, consisting essentially of sulphates and muriates of soda and potash and super-phosphates of calcium. These can be recovered by boiling the solution to dryness, and possess valuable manuring qualities. The insoluble matters remaining after the treatment with cold water must be digested in a strong solution of carbonate of potash or soda, in the cold, in order to remove from the guano all colouring matters that it may contain. The next step is to separate the uric acid from the urate of ammonia and bone earth which form the now remaining residuum. This may be effected in several ways. By treating the compound with dilute sulphuric acid, the uric acid will be liberated, and brought into a condition that will enable it to be acted upon by peroxide of lead, care being taken that the sulphuric acid present shall always be a little in excess of the proportion actually required to neutralize the ammonia. A second, and perhaps better method consists in boiling the compound in a dilute solution of soda or sodic carbonate, whereby a solution of urate of sodium is obtained, about 32 lb. of soda being required for every 168 lb. of uric acid present. This operation entails the evolution of large quantities of ammonia, which may be collected and economized by conducting the process in a still of sufficiently large dimensions to accommodate the frothing of the ammonia. The water used in separating the urate of soda from the residual earthy matters must be as hot as possible, on account of the slight solu bility of the salt in cold water, and the residue should be carefully washed free of urate of soda by boiling water. The strong solutions of urate of soda must be again treated with carbonate of soda in the same quantity as before, and then evaporated until a deposit commences to form. Left to cool, it forms a crystalline mass, from which the liquid must be pressed and drained, and the solid residue be washed with cold water. This plan enables a pale, lemon-coloured oxalate of soda to be produced even from dark-coloured guanos of the second species. Occasionally, however, the guano is so deeply coloured that the sodic urate thus obtained does not yield a sufficiently colour less oxalic acid, in which case tho salt should be once more boiled in a strong solution of sodic carbonate, thus dissolving the colouring matter, and the little urate taken up by the carbonate need not be lost, as the carbonate used in decolorising one crop may be employed to dissolve the uric acid out of a fresh sample of guano. The urate of soda is now to be added to boiling sulphuric or hydrochloric acid, the acid being in such excess as to ensure the complete separation of the soda, and the ebullition to be continued for 15 to 20 minutes.