hot water, from which it crystallizes in tufts of prisms with 2 H,. The ammonium salt crystallizes in voluminous plates and needles with H., and easily becomes red when heated. The potassium salt resembles it in composition and in appearance. Pseudo-uric is a monobasic acid, the molecule of which contains the elements of uric acid with one additional atom of water. When oxidized with peroxide of lead it does not, however, yield allantoin, but carbonic, oxalic, and oxaluric acids, whilst urea is liberated.

6

(1640) Allantoin (ЄH ̧Ñ‚Ð ̧).—This is a body which occurs in the allantoic fluid of the cow, or in the urine of the fœtal calf, but it may also be procured by the oxidation of uric acid. For this purpose, I part of uric acid must be suspended in 20 parts of water, and raised to the boiling point; finely-levigated peroxide of lead is then to be added in small quantities at a time to the boiling liquid, until the oxide ceases to change colour. The peroxide of lead is reduced to the state of protoxide, and a brisk effervescence occurs, owing to the escape of carbonic anhydride, whilst oxalate of lead is precipitated; the supernatant liquid is colourless, and on filtering it and allowing it to cool, hard, brilliant, rhombic prisms of allantoin are deposited. Upon further concentration of the solution, fresh crystals of allantoin are obtained, and when the mother-liquid has been evaporated until it acquires a syrupy consistence, crystals of urea are deposited.

Allantoin is a neutral, tasteless substance, sparingly soluble in cold water, but freely soluble in boiling water. It shows but small tendency to combine with other bodies; but a silver compound of allantoin may be obtained by mixing a boiling solution of allantoin with one of nitrate of silver, and adding ammonia drop by drop; a white precipitate (C,H,AgNO3) is thus occasioned. Allantoin undergoes fermentation in the presence of yeast, furnishing urea, ammonium oxalate, and an unexamined acid (Wöhler). When allantoin is boiled with solutions of the alkalies, it undergoes decomposition, ammonia being evolved whilst an oxalate of the alkali metal is formed:

Allantoin.

:

Potassic oxalate.

€_HN +H,O + 4 KHO = 4 HẠN + 2 K€,Đ.

61

3

+4

Allantoin is readily decomposed by simple elevation of temperature: when its aqueous solution is heated in a closed tube to about 284° (140° C.), it is resolved into a new acid, the allanturic acid of Pelouze (Є,H,N,,), and into ammonium carbonate; both these substances being produced from the elements of allantoin by the assimilation of the elements of water :

Allantoin also assimilates water and is transformed into allanturic acid by heating it gently with nitric acid, or with hydrochloric acid, and urea is at the same time formed:

Pelouze considers that the urea found in the mother-liquor, obtained during the preparation of allantoin from uric acid by means of peroxide of lead, is due to this secondary action; this, however, is very doubtful.

Allanturic acid is a white deliquescent substance, which gives white precipitates with nitrate of silver and with the acetates of lead; these precipitates are soluble in an excess of these salts, as well as in free allanturic acid. Baeyer regards allanturic acid as glyoxal urea [ЄH ̧(¤ ̧HÐ ̧)N ̧Ð].

Lantanuric Acid is the name given by Schlieper to a result obtained by adding the powdered uric acid to a solution of potassic ferricyanide and caustic potash at ordinary temperatures. Under these circumstances the ferricyanide is rapidly converted into the ferrocyanide of potassium, whilst nascent oxygen attacks the uric acid; 4 K,FeCу + 4 KH→ = 4 K ̧FeCy+ 2 H ̧бР̧. Allantoin and carbonic anhydride are first produced:

Uric acid.

6

Allantoin.

and the allantoin combining with an additional quantity of water is resolved into lantanuric acid and urea. It is probable that lantanuric acid is identical with the allanturic acid of Pelouze : it is a deliquescent substance, which forms a white insoluble salt with oxide of lead, and its properties agree very closely with those ascribed by Pelouze to allanturic acid, respecting the analysis of which he has hitherto published no details.

(1641) Hydantoin (Є ̧H ̧Ñ‚2).—There are several methods by which this body may be obtained: one consists in heating an excess of concentrated hydriodic acid with allantoin, then diluting, removing the excess of iodine by means of sulphuretted hydrogen, and the hydriodic acid by carbonate of lead. On evaporation

hydantoin is obtained in warty masses of crystals:—

Allantoin.

H.NO + 2 HI =

Hydantoin.

Urea,

824

GLYCOLURIL-GLYCOLURIC ACID-CYSTIN.

Hydantoin crystallizes indistinctly; it is moderately soluble in cold water, has a slightly sweet taste, and is neutral to litmus : it fuses at 403° (206° C.). When boiled with baryta water, it is converted with assimilation of an atom of water into hydantoic, or glycoluric acid. Baeyer has, indeed, succeeded in synthetically producing hydantoin by a process which shows it to be really glycolyl urea-by acting on urea with bromacetyl bromide he first obtains bromacetyl urea, and by heating this for some hours with an alcoholic solution of ammonia he obtains hydantoin

Bromacetyl brom.

Urea.

Urea hydrobrom.

Bromacetyl urea,

:

9

(1642) Glycoluril (Є,H.NO).-If a hot solution of allantoin, in about 30 parts of water, is acidulated with sulphuric acid, and treated with an amalgam of sodium, containing about 1 per cent. of sodium, glycoluril is deposited in octohedral crystals. This compound contains I atom of oxygen less than allantoin. If heated with baryta water, ammonia escapes, baric carbonate is deposited, and baric glycolurate is obtained in solution, from which glycoluric acid (HЄ,H,N) may be procured in transparent crystals after the removal of the barium by the cautious addition of sulphuric acid. This appears to be identical with the hydantoic acid of Schlieper and Baeyer. When dilute glycoluric acid is treated with silver oxide in excess, it furnishes an alkaline liquid, which gradually deposits a characteristic salt in fine pearly scales, and warty white tufts of needles; but on acidulating with nitric acid, or adding nitrate of silver, these pearly scales (Ag€,H,N ̧Ð ̧) are deposited immediately (Rheineck, Lieb. Annal. cxxxiv. 218). The formation of glycoluril and glycoluric acid from allantoin is easily traced by the following equations :

3

and

2

4 2

Glycoluric acid.

Urea.

The urea breaks up in the presence of baryta into carbonic acid and ammonia.

(1643) Two other substances which have been sometimes found in urine-viz., cystin and kynurenic acid, will be noticed here. Cystin, or Cystic Oxide (¤ ̧H ̧ч ̧§).—This substance constitutes a rare form of urinary calculus; its name is derived from

ALBUMINOID AND GELATIGENOUS PRINCIPLES.

825

KUOTIC, the bladder. Calculi composed of cystin are semitransparent and of a brownish-yellow colour, and crystalline texture. Cystin is insoluble in water, alcohol, and ether, but it is dissolved by the stronger acids, such as the sulphuric, nitric, hydrochloric, and phosphoric. It is also freely soluble in alkaline solutions, whether caustic or carbonated, from which it can be precipitated by the addition of an acid such as the acetic. It may readily be obtained crystallized in hexagonal plates, by allowing its ammoniacal solution to evaporate spontaneously. When heated it does not melt, but is decomposed, emitting a peculiar fœtid odour. Cystin contains 25'5 per cent. of sulphur.

(1644) Kynurenic Acid (from Kuwv, a dog) is the name given by Liebig to a peculiar acid found in the urine of the dog. It forms very light, silky, colourless, delicate needles, which are soluble in alkaline solutions, nearly insoluble in water, and insoluble in alcohol and ether. It is soluble in hot dilute acid solutions, and is deposited from them on cooling. With the metals of the alkalies it forms soluble crystalline salts. Kynurenic acid does not appear to contain nitrogen. Its composition has not been ascertained. When heated in a small tube it yields a crystalline sublimate, and leaves scarcely a trace of any carbonaceous residue.

CHAPTER XI.

ALBUMINOID AND GELATIGENOUS PRINCIPLES.

(1645) THE greater number of the compounds of organic origin which have hitherto occupied our attention are destitute of organic structure; they contain in each of their constituent or equivalent molecules only a moderate number of elementary atoms, in which respect they differ from the compounds which remain to be described, since the latter are of a much more complex constitution. These bodies enter into the formation of the organized textures, and are destitute of crystalline character. The most important of them-viz., fibrin and albumin, occur both in plants and in animals, and though they form but a small proportion of the solid and liquid components of the organs of plants, they are never entirely wanting in some portion or other of their organism. They are most abundant in the seed. These substances abound, however, in the animal tissues, and constitute their most

826 OXIDATION OF THE ALBUMINOID AND GELATIGENOUS GROUPS.

remarkable and distinctive ingredients. Owing to the complexity of their composition no satisfactory rational formula can at present be assigned to any of these azotised bodies; and, owing to their indisposition to crystallize, great difficulty is experienced in obtaining them in a state of purity, and of ascertaining when they are really free from foreign admixture. All of them contain sulphur amongst their components, though the proportion of this element never exceeds 2 per cent.

These azotised compounds may be subdivided into two groups: of these the more important is termed the albuminoid group, owing to the general resemblance of its members to albumin, or white of egg; it comprises albumin, fibrin, casein, and legumin, in which the proportion of carbon to nitrogen is that of four atoms of the former to one of the latter. The second group is the gelatigenous : it comprises gelatin, chondrin, and ossein.

(1646) Products of Oxidation of the Albuminoid and Gelatigenous Groups.-When these azotised substances are submitted to the gradual action of oxidizing agents, they furnish a great variety of products, which, however, belong to three principal groups; viz., to the acetic, the benzoic, and the cyanic series. Amongst the volatile bodies furnished by treating albuminoid substances with a mixture of potassic dichromate and sulphuric acid, or with a mixture of peroxide of manganese and sulphuric acid, Guckelberger (Liebig's Annal., Ixiv. 39) obtained the following products, besides others which have not been specially identified :

The volatile products of oxidation are the only ones which have as yet been fully examined. The most abundant of these products are the series of volatile acids: next to these the products of the benzoic series occur in the largest quantity, whilst the hydrocyanic is obtained in the smallest quantity. The proportion in which these substances are formed varies according as casein, fibrin, albumin, or gelatin has been the body submitted to oxidation. Gelatin yields the largest quantity of formic, acetic, and valeric acids (Schlieper, Liebig's Annal., lix. 1); fibrin gives the largest proportion of butyric acid, and casein yields the compounds of