(1616) Alanine (,H,NO).—The interest attaching to this base arises from its homologous relation to glycocine, and to its connexion with lactic acid. It is isomeric with lactamide, with sarkosine, and with urethane, but is perfectly distinct from all of them, being, in fact, amidopropionic acid [HE,H,(H,N)→]. Alanine, as it was arbitrarily named by Strecker, is obtained by distilling an aqueous solution containing two parts of aldehydammonia (1249) and one of hydrocyanic acid with an excess of hydrochloric acid. Traces of hydrocyanic and formic acids pass over with the excess of hydrochloric, but no aldehyd. The liquid in the retort is concentrated by evaporation, and a considerable proportion of ammonia hydrochlorate is separated in crystals. The mother-liquor retains alanine hydrochlorate it must be boiled with hydrated oxide of lead, which is to be added in small portions to the boiling liquid until it ceases to occasion a disengagement of ammonia. The liquid is then to be decanted from the precipitate, treated with sulphuretted hydrogen to remove the excess of lead, filtered and evaporated. Alanine crystallizes out, and if the mother-liquor be mixed with alcohol, it furnishes an additional quantity. The reaction by which alanine is formed may be thus represented :

Aldehyd-ammonia,

Alanine.

Sal ammoniac.

Í ̧Ñ‚¤‚Í ̧Ð + HЄN + HCl + H2→ = ¤ ̧μ‚NÐ ̧ + H ̧NCI.

Alanine crystallizes in groups of colourless prisms, which are soluble in between 4 and 5 parts of cold water, but are very sparingly soluble in alcohol, and insoluble in ether. Its aqueous

solution has a very sweet taste: it is without action upon testpapers. Alanine may be partially sublimed at a temperature a little above 401° (205° C.). If heated suddenly, it melts and is decomposed, becoming converted into ethylia and carbonic anhydride when heated on platinum foil it burns with a violet flame. Caustic potash decomposes it, ammonia and hydrogen are disengaged, whilst potassic acetate and cyanide are obtained. When distilled with dilute sulphuric acid and peroxide of lead, carbonic anhydride, aldehyd, and ammonia are formed. But its most interesting metamorphosis is that which it undergoes when the aqueous solution is treated with nitrous acid, in which case lactic acid is formed, whilst nitrogen is liberated :—

Alanine, like glycocine, forms numerous compounds both with

acids and with bases; many of them may be obtained in crystals, but they are all very soluble.

11

The compounds (EH,NO2) and (ЄH1NO), intermediate between alanine and leucine, in the glycocine series, and corresponding to the aldehyd ammonias of propionic and butyric acids, have not as yet been prepared, but according to Gorup Besanez the butyric compound accompanies leucine in the pancreas of the ox.

6 13

(1617) Leucine, Caseous Oxide, or Aposepedine (¤ ̧H1NO2).— Various decompositions give rise to the formation of this body, which may be viewed as amido-caproic acid [H¤ ̧H10(H2N)→2]. It is one of the products of the putrefaction of casein, or of cheese, of muscle, and of gluten, in the presence of water; and it is also amongst the compounds obtained by the action either of sulphuric acid diluted with 3 or 4 parts of water, or of caustic potash, upon gelatin, muscular tissue, the yellow elastic tissue of the ligamentum nucha, white of egg, horn, and wool. One of the best methods of obtaining leucine consists in fusing dried casein or any other albuminoid substance with its own weight of caustic potash; during this operation ammonia is evolved, and a disgusting fæcal odour is emitted: as soon as hydrogen begins to come off, which is indicated by the change of colour from dark brown to yellow, the mass must be allowed to cool; and on treating it with hot water, a highly alkaline liquid is obtained, which contains in solution leucine and tyrosine (Bopp, Liebig's Annal. Ixix. 21). On slightly supersaturating the liquid with acetic acid, tyrosine is deposited in concentric groups of needles; and on further evaporation of the mother-liquid, leucine is obtained in pearly colourless plates, which may be purified by washing them with alcohol, and recrystallizing the residue from boiling dilute alcohol. Limpricht has also succeeded in obtaining leucine artificially, by boiling the compound of valeric aldehyd and ammonia with an excess of hydrocyanic and hydrochloric acids, until the oily liquid produced by the fusion of the valeraldehyd-ammonia has disappeared in this manner sal ammoniac and leucine are obtained :—

The excess of hydrochloric acid may be removed by means of oxide of lead, and the traces of lead may be separated by hydrosulphuric acid, after which the liquid is evaporated in a water-bath: boiling dilute alcohol then dissolves leucine from the residue, and deposits it in plates as it cools.

Cloetta has made the interesting observation that leucine is one of the normal constituents of the pulmonary tissue; and by operating upon considerable masses of bullocks' lungs he procured it associated with taurin, inosin, and uric acid. It has also been found as a normal constituent of the spleen (Stædeler) and pancreas, and has been obtained from the urine in cases of typhus and affections of the spinal cord.

Leucine somewhat resembles cholesterin in appearance, and derives its name from Aɛuкòs, white; it has an unctuous feel, and is lighter than water. When heated cautiously, leucine may be sublimed before it melts, without undergoing decomposition, and may be collected in the form of woolly flocculi. At a higher temperature it becomes brown, and melts at about 338° (170° C.), and when heated a little beyond this point it furnishes a distillate composed of a yellow oily liquid, containing free ammonium carbonate, whilst a brown resinous substance remains in the retort. The oily distillate consists chiefly of amylia. Leucine is sparingly soluble in cold water, but freely so in boiling water. The presence of acetic acid or of potassic acetate favours its solution both in water and in alcohol. Cold absolute alcohol dissolves it very sparingly, and it is insoluble in ether. It is, however, easily soluble in dilute solutions of the acids, with many of which it forms crystallizable compounds; leucine hydrochlorate (H1NO2,HCl) is very soluble in water; the nitrate or nitroleucic acid (H1NË,,HNƏ ̧) crystallizes in colourless needles. An aqueous solution of leucine occasions a white precipitate with basic acetate of lead; and if to a boiling solution of leucine mixed with the normal acetate of lead, ammonia be cautiously added, pearly scales (Pbе, 2 ЄH1NO) are deposited. Leucine also precipitates mercurous nitrate (Braconnot), but no other metallic solutions.

6 131

6 131

Leucine, when distilled with peroxide of lead, furnishes ammonia and butyric aldehyd. If it be distilled with dilute sulphuric acid and peroxide of manganese, valeronitrile with carbonic anhydride and water is produced :

If a solution of leucine be treated with chlorine in excess, carbonic anhydride is liberated, and a mixture of valeronitrile and chlorvaleronitrile is obtained, which is separated in the form of volatile oily drops, whilst a quantity of leucine hydrochlorate is formed in the retort (Schwanert).

If leucine be fused with caustic potash it yields potassic valerate and carbonate, whilst ammonia and hydrogen are liberated :—

Pure leucine is stated also to undergo a similar decomposition when caused to ferment, by the addition of a small quantity of muscular fibre, or of albumin. When an aqueous solution of leucine is submitted to the action of nitrous acid, the leucine is decomposed with liberation of nitrogen and the formation of leucic acid (H,H), just as glycolic and lactic acids are formed from glycocine and alanine under similar circumstances.

(1618) Tyrosine (Є,H,,NO,; Hinterberger).-This substance was obtained by Liebig from the products of the fusion with caustic potash of well-dried fibrin, albumin, or cheese (hence its name, from Tupòs, cheese): the process must be conducted in the manner described when treating of the preparation of leucine. The crude crystals of tyrosine must be redissolved in a solution of potash, and precipitated with acetic acid. If coloured it must be converted into hydrochlorate, digested with animal charcoal, and the filtered liquid whilst boiling must be mixed with potassic acetate; potassic chloride is thus formed, and tyrosine, free from acetic acid, is deposited in long fibrous crystals. Tyrosine is also found among the products of the putrefaction of albumin, fibrin, and casein; and it is produced, together with leucine, when these albuminoid bodies are boiled for some hours with dilute sulphuric or hydrochloric acid. Horn, feathers, and hair, also yield it by this treatment:-one part of horn, 4 of oil of vitriol, and 12 of water, if boiled for forty hours, furnish a dark brown fluid, which at the end of that time must be rendered alkaline by the addition of milk of lime, then heated and filtered: sulphuric acid must now be added to neutralization, and on evaporation, crystals of tyrosine will be deposited; they may be purified in the manner already directed.

Tyrosine in certain cases is a direct product of the chemical actions in the living animal; it was found by De la Rue ready formed in the cochineal insect, and has been met with in the pancreas and other internal organs of the higher animals, as well as in the urine in typhus, and in certain spinal affections.

Tyrosine forms long fibrous crystals, which are very sparingly soluble in cold water, and nearly insoluble in alcohol and in ether ; boiling water dissolves it in considerable quantity. Although its solutions are neutral to test paper, it is freely soluble both in acid

9 9

3

URIC, OR LITHIC ACID.

801

and in alkaline solutions; it combines with two atoms of a monad or one of a dyad, forming compounds like that with barium (¤‚Í‚Bа”NÐ ̧‚H,O). With sulphuric acid it forms a colligated crystallizable acid; if this be neutralized with lime, and mixed with ferric chloride, it gives a characteristic violet solution. By cautious distillation tyrosine may be almost wholly converted into ethyloxyphenylia and carbonic anhydride (Schmitt and Nasse) :

:

When treated with hot nitric acid, tyrosine yields oxalic acid; and if cold dilute nitric acid be employed, nitrotyrosine nitrate [Є,H10(NO)NO,,HNO3] is formed. A very delicate test of the presence of tyrosine is afforded by the formation of a red flocculent precipitate when its solution is heated with a nearly neutral solution of mercuric nitrate, and if the solution be very dilute a rose-red colour is developed in the liquid (R. Hoffman). Tyrosine is probably the ethylo-amidic acid of paroxybenzoic acid (Barth). The potassic paroxybenzoate may be obtained by fusing tyrosine with an excess of caustic potash. The relation between tyrosine and paroxybenzoic acid is seen by comparing the formula which follow :

:

5 ༡༤ 4

4

(1619) URIC, OR LITHIC ACID (H,H ̧Ñ‚Ð ̧, or C1H,N,O= 168). This important excrementitious product occurs in small quantity in human urine. It is much more abundantly contained in the white, semi-solid excretions of birds; and, in combination with ammonia, it constitutes almost the whole of the excrement of serpents, such as the boa. The beds of guano found in the rainless islands of the Pacific, which are formed of the accumulated excrements of countless generations of sea-fowl, consist chiefly of ammonium urate, which has undergone decomposition more or less extensive. When uric acid is secreted in excess in man, it is often deposited from the urine in the form of hard crystalline grains, forming what is commonly termed red gravel; or it collects into larger masses which, if retained in the bladder, generally acquire considerable size, and constitute the most usual variety of urinary calculus. In gouty patients also uric acid not unfrequently accumulates around the joints affected: