cohol of 98 per cent. strength (Zollikofer). It is insoluble in ether, even when boiling. The presence of acetic acid and acetate of potash increases the solubility of leucine in alcohol and water. When heated cautiously in a glass tube, open at both ends, it is completely volatilized in the form of thick white fumes, appearing like oxyde of zinc, without previously melting. When heated suddenly it fuses, and leaves a mass of charcoal. It is easily soluble in dilute acids, and forms combinations, assuming readily a crystalline form. It is also easily soluble in ley of caustic potash, and in ammonia. Decompositions.-When fused with caustic potash, it is decomposed into valerianate of potash, cyanide of potassium, and water, free hydrogen escaping.

C12H12NO+2KO, HO=C,H,KO ̧ + KC2N + H2 + 3HO.

13

Leucine.

10

Under the influence of nitrous acid, leucine is transformed into leucic acid (Strecker),' nitrogen escaping.

2(C12H13NO4) + 2NO3 = C2H2O12 + 4N + 2HO.

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Zollikofer (1852) found that the watery solution of leucine is not precipitated by salts of metals, not even by the nitrates of the protoxyde and suboxyde of mercury, nor by corrosive sublimate; basic acetate of lead being the sole exception to this rule. This has been confirmed by Goessmann (1854). It is therefore a great oversight on the part of authors of systematic treatises on organic and medical chemistry, to continue to state in 1854 and 1857, what in 1852 had been proved to be incorrect.

Salts of Leucine.2-The combinations of leucine with acids may be produced in a direct manner.

Hydrochlorate of Leucine (C12HNO, HCl) forms crystals easily soluble in water.

Nitrate of Leucine, or Leuconitric Acid (C12H1NO NO,H), appears in colourless concentric groups of needles. It forms a salt with lime, crystallizing in small warts, and containing water of crystallization; and another salt with magnesia, appearing in small granular crystals.

1 Ann. d. Chem. und Pharm.,' lxxii, p. 89.

Gerhardt, Laurent, and Cahours, Compt. Rend.,' xxvii, pp. 256, 265.

With nitrate of silver, leucine forms a crystallizable compound.

Leucine enters into combination with the oxydes of several metals.

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Leucine and Oxyde of Copper. C12HNO C12HINO CuO.-Hydrated oxyde of copper, when just precipitated, dissolves in a solution of leucine, easily, and in large quantities, forming a blue fluid. When this solution is evaporated on the waterbath, blue crystals of the above compound are obtained, which are very similar to the ammonio-sulphate of copper. If a solution of leucine is boiled with an excess of hydrate of oxyde of copper, the above soluble compound and an insoluble one are formed.

Leucine and Oxyde of Mercury. It may be prepared like the copper compound, or by neutralizing with potash a mixture of solution of nitrate of protoxyde mercury and solution of leucine. It contains one equivalent of protoxyde of

mercury.

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Leucine and Oxyde of Lead. C2H3NO, PbO.-When to a boiling mixture of solution of leucine and neutral acetate of lead ammonia is carefully and gradually added, little scales of the lustre of mother-of-pearl are deposited (Strecker).

If a solution of leucine is boiled with an excess of oxyde of lead, or if to a boiling mixture of solutions of leucine and acetate of lead ammonia is added in excess, an insoluble compound of the formula C12H13NO4, (PbO), is produced (Goessmann).

Mode of obtaining Leucine from Urine.

The above tests with lead may perhaps be made available for that purpose. I have obtained leucine as a deposit by concentration of the urine. The deposit may be washed with cold alcohol, and purified by lime, charcoal, and so on; or in one of the ways indicated above. All this will only serve to prove its presence: we have, as yet, no means for determining its quantity.

TYROSINE.

Elementary composition: C8H11NO6.

The occurrence and mode of obtaining tyrosine have already been described. It was discovered by Liebig as a product of the decomposition of cheese by fused caustic potash.

Physical and Chemical properties.

It crystallizes in voluminous white needles, which on drying contract to a silky film of white colour and some lustre. As such I obtained it from the inspissated watery extract of the liver. It is without taste or odour.

In cold water it is scarcely soluble, easily in boiling water. It is insoluble in alcohol and ether. It dissolves rapidly in mineral acids and alkalies, yielding compounds which are even soluble in alcohol. From a solution in ammonia, it crystallizes unchanged, but in larger crystals on spontaneous evaporation of the fluid. From the alkaline solution it is precipitated by acids. Heated on the platinum foil, it burns without leaving any residue, emitting the odour of burnt horn.

When tyrosine is dissolved in strong nitric acid, the solution, after a short time, yields brownish-yellow crystals of nitrate of nitrotyrosine, CH10XNO6, HO, NO5.

From its formula, tyrosine may be considered to be a copulated compound of glycocoll and saligenine.

C18H11NO6 = C1H ̧ÑO + C1H ̧О—2HO.

Under the influence of boiling nitric acid, tyrosine is decomposed, oxalic acid being one of the principal products. Nitrate of protoxyde of mercury causes a precipitate of red flakes in a solution of tyrosine while boiling. The precipitate subsiding to the bottom, leaves a clear fluid above it, which has an intensely pink or dark rose-red colour. This test is so nice, that it is obtained even when the watery solution of tyrosine, saturated at the ordinary temperature of the air, is diluted several times with its own volume of water (R. Hoffmann).

If some tyrosine and one or two drops of sulphuric acid are placed on a watch-glass, covered, and allowed to stand for about half an hour, and the mixture is then diluted with water, neutralized with carbonate of lime and filtered, and if to the filtrate a solution of chloride of iron is added, containing no free acid, a rich violet colour is immediately produced. Neutral chloride of iron will produce this test with all neutral salts of the tyrosino-sulphuric acid.

Tyrosine was discovered in the urine of typhus patients by Frerichs and Städeler. It is most probably formed in the liver, together with leucine.

2

XANTHINE, or xanthic oxyde, was discovered by Dr. Marcet,' in 1819, and was first analysed by Wöhler and Liebig, afterwards by Laugier. It has as yet been found in three instances only, forming calculi from the urinary bladder of man. It contains one equivalent of oxygen more than hypoxanthine, from which, in its reactions, it is only distinguished by its insolubility in water.

Urinary calculi consisting of xanthine are light or dark yellowish-brown in colour, of even surface, hard in substance, of the hardness of the ordinary uric acid calculi, constructed of concentric layers without fibrous or crystalline texture. On friction the calculi assume the glistening appearance of

wax.

Mode of obtaining Xanthine from Calculi.

The calculus is dissolved in caustic potash, and the filtrate precipitated by a current of carbonic acid. The precipitate, which is white and pulverulent, is washed, and on drying

1 'Essay on the Chemical History and Medical Treatment of Calculous Disorders,' London, 1819.

·

2 Poggend. Annal.,' xli, 393. Ann. d. Pharm.,' xxvi, 340.

3Journ. de Chim. Med.,' v, 513. See Gmelin, Handb. d. Organ. Chem.,' 4to edit., 1852, vol. ii, p. 514, whence the article is transcribed.

forms into hard yellowish pieces, which become wax-like on friction, and are free from potash.

Chemical properties.

Subject to dry distillation, the xanthine calculus yields much prussic acid, and a sublimate of carbonate of ammonia, but no urea. Heated before the blowpipe, it breaks into pieces, blackens, emits a peculiar weak odour of burning animal matter, which is different from that of burning uric acid, and more like that of burnt horn, and then is burned, leaving only little ashes.

Its solution in nitric acid, on evaporation, leaves a lemonyellow dry residue, which is partly soluble in water; this solution is yellow, becomes discoloured with acids, reddened by the addition of caustic potash, and then yields a carmine mass on evaporation, which is soluble in water with a yellow tinge. The solution in caustic potash gives a yellow precipitate with hydrochlorate of ammonia, and is decomposed by liquor soda chlorinatæ, the solution becoming dark at first, then colourless, under evolution of nitrogen gas.

Xanthine is slightly soluble in boiling water, from which solution it is precipitated on cooling in the form of a thin membranous layer.

It is soluble in oil of vitriol, and is not precipitated from this solution by the addition of acids. In dilute acids it is very little soluble. It is insoluble or scarcely soluble in hydrochloric acid.

It is more easily soluble in ammonia than uric acid, and the solution on evaporation leaves a yellowish lamellated mass, containing yet some ammonia.

It readily dissolves in caustic potash, and is precipitated from the solution by acids. The solution is dark greenishbrownish-yellow, like bile, and deposits xanthine immediately, when a current of carbonic acid gas is being transmitted through the fluid. The addition of hydrochlorate of ammonia to the solution also causes a precipitate, but only on evaporation, during which ammonia is being evolved.

Xanthine is soluble in a watery solution of carbonate of potash, insoluble in bicarbonate of ammonia, potash, or soda.

It is a little soluble in acetic acid.

It is insoluble, or scarcely soluble, in oxalic acid.

It is insoluble in spirits of wine and ether.