a milk-white crystalline mass. By dry distillation it yields a red oil, which has the odour of the Tonka bean ("the pride and flower of the snuff-box"), ammonia, and benzoic acid (the latter two, perhaps, in part as benzoate of ammonia) and a large residue of charcoal. Sometimes the acid before charring evolves a cyanogen compound, having the odour of hydrocyanic acid. If the temperature during dry distillation be not raised above 482° F. (250° C.), benzoic acid is obtained, slightly reddened, a trace of hydrocyanic acid, and benzonitrile is collected in the receiver.

Hippuric acid is soluble in warm nitric acid, and hot hydrochloric acid, and from both solutions crystallizes on cooling; but when boiled for some time in either of these solutions it undergoes a decomposition, by which benzoic acid crystallizes out of the solution on cooling.

Combined with the nitric acid there remains glycine, or glycocoll, or sugar of gelatine. This decomposition may also be produced by sulphuric and oxalic acids, and by boiling with caustic soda or potash. From this mode of decomposition Dessaignes concluded that hippuric acid was a combination of benzoic acid and glycine, and that by the artificial combination of these two bodies hippuric acid might be produced. He succeeded in producing hippuric acid by exposing a combination of glycine with oxyde of zinc to the influence of chlorine-benzoyle.

Under the influence of a ferment, in the presence of an alkali, hippuric acid undergoes the same decomposition into benzoic acid and glycocoll. The disintegration of hippuric acid in putrefying urine is thus satisfactorily explained.

18 8

Hippuric acid is the amide of a new acid, benzoglycolic acid, which is free from nitrogen, and has the composition CHO. It is formed when hippuric acid is acted on by hyponitrous acid, and is obtained by conducting a current of oxyde of nitrogen through a solution of hippuric acid in nitric acid.

C18H2NO+NO, C1HO+2N + HO.

Hippuric acid.

Benzoglycolic acid.

Benzoglycolic acid crystallizes from the solution in colourless prisms, which are easily soluble in alcohol and ether, but sparingly soluble in water. It forms neutral salts with one equivalent of base, which are mostly crystallizable. The limesalt, CaO, CH,O,, crystallizes in colourless needles, and has a tendency to form oversaturated solutions.

Buchner, Ann. d. Chem. und Pharm.' Ixxviii, p. 203.

2 Socoloff and Strecker, 'Ann. d. Chem. und Pharm.,' lxxx, p. 17.

When benzoglycolic acid is treated with dilute acids it is decomposed to benzoic and glycolic acid after the formula.

This decomposition explains why hippuric acid, although it be the amide of benzoglycolic acid, does not yield that acid and ammonia when boiled with acids, but benzoic acid and glycocoll. The benzoglycolic acid is at first formed along with ammonia, but is immediately decomposed into benzoic and glycolic acid, and the latter, with the ammonia, forms its amide, glycocoll, and water.

Hippuric acid, when treated with oxydizing agents,' e. g., peroxyde of lead in water, yields benzamide, carbonic acid, and water, according to the following formula.

C18H9NO=C14H,NO2+4CO2+2HO.

Hippuric acid. Benzamide.

Compounds of Hippuric Acid.

Nitrohippuric acid.2 C8H8N2O10--To a solution of hippuric acid in cold fuming nitric acid, an equal volume of oil of vitriol is gradually added, care being taken not to let the mixture get hot. After two hours the reaction is completed. The fluid is now mixed with three times its volume of water, being continually kept at a low temperature. The mixture, after twelve hours, has deposited about one half of the hippuric acid employed in the form of nitrohippuric acid in needle-shaped crystals. The mother-liquor, when neutralized by carbonate of soda until it begins to get turbid, deposits another quantity of the acid. The impure acid is washed with cold water, combined with lime, and the solution of the lime-salt in lukewarm water is precipitated by hydrochloric

acid.

Nitrobenzoic acid may be taken internally, in quantities amounting to 6 grammes per diem, without injury to the system. It reappears as nitrohippuric acid in the urine, from which it may be obtained by the following proceeding. The acid urine is evaporated to a small bulk. It remains clear on the addition of hydrochloric acid; the fluid is now shaken Fehling, Ann. d. Chem. und Pharm.,' xxviii, p. 48. Bertagnini, Compt. Rend.,' xxxi, p. 490.

with ether and some alcohol, which take up nitrohippuric acid, and, on spontaneous evaporation, deposit it in brown warty crystals, which, when removed from the mother-liquor, dried on a brick, and recrystallized from hot water, appear as brownish needles. When boiled for five minutes with excess of milk of lime, colouring matter is removed, and the filtrate, on decomposition by hydrochloric acid, yields pure nitrohippuric acid, which is obtained in fine crystals by recrystallization from hot water.

Hippuric Acid Salts-Hippurates.

But as

The alkaline and earthy hippurates are soluble in water. Hippurate of soda seems to be a combination which occurs in human urine. But as hippuric acid in human urine, when present in larger quantities, crystallizes on simple evaporation on the surface of the fluid, there is, à priori, great probability that it may also be present in a free state. it cannot easily have existed as such in the blood, an explanation would be required of the agency by which, in the moment of secretion, or afterwards, it was deprived of its base. This must at present remain a subject for future inquiry. In the urine of the horse hippuric acid is combined with lime. Metallic hippurates are sparingly soluble. All hippurates yield their bases to hydrochloric acid, hippuric acid crystallizing from the solution in delicate silky needles.

The hippurates may be basic, neutral, or acid salts; that is, containing either one half, or one or two equivalents of acid to one of base.

Hippurate of baryta, neutral. C, BaH,NO+HO (crystals). By dissolving hippuric acid in excess of baryta water, and precipitating the excess of baryta by a current of carbonic acid, or by boiling an excess of carbonate of baryta in a solution of hippuric acid, a solution of neutral hippurate of baryta is obtained after filtration, which on evaporation yields the salt in crusts, consisting of microscopic quadratic prisms. Hippurate of lime. CCaH NO+3 HO.-By boiling an excess of carbonate of lime in a solution of hippuric acid, a filtrate is obtained, which on evaporation deposits this salt in rhombic prisms, or glistening scales. It is also obtained by boiling a solution of hippuric acid with excess of milk of lime, filtering, and passing a current of carbonic acid gas through the solution. The filtrate contains the salt. This compound is said to occur in the urine of the horse and cow. It is soluble in 18 parts of cold, and 6 parts of boiling water.

18

Hippurate of lead, neutral, C, PbH NO+3HO, is obtained by mixing the hot solution of an hippurate with solution of acetate of lead; on cooling the salt is deposited in lamina of the lustre of mother of pearl. If cold solutions of lead and hippurate are mixed, the salt precipitates at once in cheesy flakes, which are with difficulty soluble in boiling water. The precipitate may be washed on a filter, dissolved in boiling water, and after filtration while boiling hot, on a funnel, kept hot, is obtained from the cooling solution in silky groups of fine needles. These needles contain only two equivalents of water of crystallization, but frequently transform into the salt with three equivalents of water, by suddenly taking up one equivalent of water under circumstances not yet accurately known. A basic hippurate of lead is obtained by boiling hydrated oxide of lead in a solution of hippuric acid.

Hippurate of iron.-The soluble hippurates cause a rusty brown precipitate in salts of the oxyde of iron. Neutral sesqui-chloride of iron produces a light isabell yellow voluminous precipitate in a cold solution of hippurate of potash, which in hot water, or by drying at a temperature of 30° C., looses water, and forms a brown mass like Canada balsam. It is insoluble in water, easily soluble in spirits of wine, particularly in hot spirits, and from the solution separates on cooling, partly in amorphous masses, partly in groups of red oblique rhombic prisms.

The salts with cobalt, nickel, copper, mercury, and silver, present no peculiarities.

Deposits of Hippuric Acid.

As the type of hippuric acid deposits we may consider the crystals which form, on evaporation, in urine containing the acid in solution. They are the long needle-like rhombic prisms in a variety of combinations, the crystals forming in groups of a stellar arrangement. The characters which, I may say, distinguish the hippuric acid deposit at first sight from the uric, are the small amount of colouring matter it contains, the needle-like habitus, and the stellar arrangement. The hippuric acid crystals have a tendency to become club-shaped at their ends. This tendency eventually ends in the apposition of many acicular crystals to the end, or both ends, of a single prism.

Ι

Deposits of hippuric acid are by no means common. have seen only two instances of this kind; and in one of them benzoic acid had been administered as a medicine. The

second case was that of a young married lady, who suffered from a severe attack of colic. The observation is, however, not sufficiently accurate to be recorded at full length. Vogel' has observed several times that needle-like crystals of hippuric acid projected like spears from larger crystals of uric acid. In such a case it is best to collect the deposit on a filter, and afterwards to boil it in alcohol. The alcoholic solution leaves the crystals of hippuric acid on evaporation.

The deposits of hippuric acid are by no means due to the same individual causes as those of uric acid, though the same causes may co-operate to produce such deposits. For, hippuric acid being more soluble in water, it follows that the acid must be present in excess before any deposit can take place. This is known to be not requisite for a deposit of uric acid. Any sediment of hippuric acid can therefore only have been produced by the co-operation of two causes: 1, an acid present in the urine, to separate hippuric acid from its base; 2, an excess of hippuric acid over the saturating point of the urine at a certain temperature.

Quantity of Hippuric Acid secreted in twenty-four hours.

Beyond the assertion of Liebig that hippuric acid was present in human urine in about the same proportion as uric acid, we possess no observations on this point. These observations are the more necessary, as Duchek has negatived the opinion of Liebig, now generally received, that hippuric acid is a constant constituent of human urine.

Physiology.

Benzoic acid, introduced into the stomach, appears in the urine as hippuric acid. One or several drachms of benzoic acid in a glass of grog may thus be taken; and, after the slight irritation of the glottis has passed away, not the least inconvenience is experienced by the individual subjected to the experiment. I observed, however, that a strong feeling of sickness followed the ingestion of a dose of one drachm in a glass of grog. It disappeared in the course of half an hour. Benzoic acid appropriates to itself glycine. The question now arises, where that combination takes place, whether in the intestinal canal, in the portal blood, in the liver, or in any other part of the system? This question must be

1 Loc. cit., p. 201.