When urine is allowed to percolate through animal charcoal in the manner described in the preceding Paper, several organic substances are absorbed and separated by the charcoal in addition to the fatty acid there referred to. The liquid obtained by treating the charcoal with boiling alcohol yields on evaporation a syrupy residue, of which a great part dissolves in water, the fatty acid being left undissolved. The filtered liquid on being again evaporated leaves a brown syrup, among which a quantity of yellowish crystals is formed on standing. On treating the mass with cold alcohol, the syrupy portion, consisting of urinary extractive matter, is removed, the crystals being left undissolved. The latter are filtered off, washed with alcohol, and then dissolved in boiling water. The solution, which has a slightly yellow colour, is evaporated to a small volume, and the crystals, which separate on standing, are pressed between blotting-paper 'and then dissolved in a little boiling water to which a small quantity of animal charcoal is added. The filtered solution, if tolerably concentrated, becomes on cooling almost solid, from the formation of a quantity of white crystalline needles, which, after the liquid has been drained off, only require drying. The substance as thus prepared consists of pure oxalurate of ammonia, since it is found to possess both the properties and the composition of that salt, as I shall now proceed to show. The crystals of which it consists are mostly small, and exhibit, even when magnified, few well-defined forms. When a few drops of the watery solution are allowed to evaporate spontaneously on a slip of glass, the residue, when viewed under the microscope, is found to consist mainly of groups of crystals arranged round centres in various irregular forms, the larger ones being composed of prisms, which are acuminated, jagged at the edges, and transversely striated, the smaller ones of needles arranged in star-shaped, double fan-shaped, or circular masses. Occasionally isolated crystals are seen, having the form of rhombic plates, some of which have two of their opposite angles truncated. I have not yet had an opportunity of comparing these forms with those exhibited by the oxalurate of ammonia obtained; directly from uric acid. The substance is tolerably soluble in boiling water, but very slightly soluble in boiling alcohol, the little which dissolves in the latter being deposited, on the solution cooling, in fine needles arranged in stars. The watery solution is neutral to test-paper; but on allowing a drop to fall on blue litmus-paper, and exposing the latter to the air for some hours, the spot will appear quite red. The watery solution, on being mixed with hydrochloric or nitric acid, yields a white crystalline deposit (oxaluric acid), which, on being left in contact with the acid liquid, gradually disappears. If nitric acid has been employed and the solution, after the deposit has dissolved, be spontaneously evaporated, amass of crystals is left, some of which have the well-known form of nitrate of urea, while the others are prismatic, and consist doubtless of oxalic acid. If the solution, after the addition of any strong acid, be boiled, oxalic acid may after a few moments be detected in it. The watery solution gives no precipitate with chloride of calcium, not even on the addition of ammonia; but on boiling, an abundant precipitation of oxalate of lime takes place. If a tolerably concentrated solution be mixed with chloride of calcium and left to stand, it deposits after some time a quantity of prismatic lustrous crystals, consisting doubtless of oxalurate of lime. The watery solution gives no immediate precipitate with nitrate of silver; but after a few moments it begins to deposit white crystalline needles, which, if the solution was concentrated, increase to such an extent as to fill the whole liquid. These needles are silky in appearance, and do not blacken on exposure to the light, but only become slightly yellow; they dissolve easily in ammonia, but no reduction takes place on boiling the solution. The watery solution of the substance gives with acetate of lead a copious crystalline deposit, and if this.be filtered off, the solution yields on standing a crop of small lustrous crystals. These crystals, when examined under the microscope, are found to have very regular forms, consisting of elongated four-sided prisms, with six terminal faces, Whether this form is the same as that of the oxalurate of lead, prepared with acid obtained from the usual source, I cannot say, as I have been unable to find any description of the salt in the books. The watery solution gives no precipitate with perchloride of mercury; but on the addition of chloride of zinc it deposits after some time a quantity of white, hard crystalline grains, which, after being filtered off and washed, are found to contain no chlorine, and on being heated, melt and burn, leaving a white residue of oxide of zinc. If the substance is dissolved in dilute hydrochloric acid, and the solution, after the addition of bichloride of platinum, is evaporated to dryness, the residue on being treated with cold alcohol dissolves partly, a quantity of shining yellow crystals, consisting of chloride of platinum and ammonium, being left undissolved.
β-l-Aspartyl-l-histidine, a Normal Constituent of Human Urine
