alcohol leaves undissolved is a bright blue powder, having the properties of indigo blue. It dissolves in an alkaline solution of protoxyde of tin, and the solution on exposure to the air becomes covered with a blue film. It is soluble in concentrated sulphuric acid, forming a blue solution, which remains blue even after dilution with water. It imparts to boiling alcohol a bright blue colour, and the solution on cooling and standing deposits blue flocks. When heated in a tube, it gives a purple vapour, which forms on the colder parts of the tube a blue sublimate.

Metamorphoses of Indigo blue.

I have already mentioned the most important metamorphoses of indigo blue, when detailing the modes of obtaining it pure and the evidence of the identity of indigo blue and uroglaucine. It may be well to recapitulate theoretically these metamorphoses, and to add those not yet mentioned.

By the reduction of indigo blue, indigo white is obtained. This process is effected according to the following formula:

By the oxydation of indigo blue, we obtain in the first instance isatine, which contains two equivalents of oxygen more than indigo blue.

Under the continued influence of oxydizing agents, such as nitric acid, isatine is transformed into nitro-salicylic acid, lastly into picric acid. The compounds obtained from isatine by chemical substitution are very numerous. Under the influence of ammonia it forms a series of remarkable amides.

Under the influence of a concentrated solution of caustic potassa and boiling, giving free access to the air, or adding manganese to the mixture, anthranilic acid is being formed. The substance having the composition of this acid was obtained by Schunck from urine, by the action of strong acids. It remains to be ascertained whether this substance is identical, or only isomeric with anthranilic acid.

The formation of anthranilic acid from indigo blue takes place after the following formula:

C16H2NO2+ 2HO +40=C14H,NO4 + 2CO2.

Schunck has succeeded in obtaining indigo blue from urine in so great a number of instances, that it is probable that indican will in future have to be placed among the normal constituents of urine. It certainly occurs more frequently than any of the abnormal ingredients of urine. Urines containing this substance exhibit no remarkable or peculiar appearance whatever; they are acid, clear, and of the usual colour. Its occurrence, at least if its quantity is moderate, is not to be considered as a pathological phenomenon. presence is not attended by any symptoms of ill health, or feelings of discomfort. The state of health and the appearance of the urine do not permit any conclusions to be drawn as to the presence or absence of this indigo-producing sub

stance.

Its

A small number of samples of urine from patients, which Schunck had an opportunity of examining, yielded, with one exception, no more indigo blue than the generality of healthy urines. Heller, however, found more uroxanthine to be present in the urine from persons labouring under diseases of the serous membranes, the kidneys, and the spinal marrow. Perhaps concentration is mainly the condition upon which the success of a search for indigo in urine depends. Virchow could obtain indigo blue from every concentrated urine. Now, as the urine of patients is mostly a fluid of a much higher specific gravity than the urine of healthy individuals, these different observations would herein find a reconciliation.

The physiological quantity of the chromogen in urine must be exceedingly small. By working for several weeks on the urine of two individuals, which contained a comparatively large quantity of chromogen, Schunck obtained one grain of indigo blue.

The urines of forty different individuals, all of whom were apparently in a good state of health, yielded, with one exception only, more or less indigo blue, when examined in the manner described. These individuals belonged to both sexes, and they were of ages varying from seven to fifty-five. The

majority were persons of the working classes. The largest quantity of indigo blue was obtained from the urine of a man above the age of fifty, a publican by trade. The urine of a young man, aged thirty-two, a servant, yielded almost as large a quantity. Among the rest, the urine of a young man, aged twenty-five, an engraver; that of a clerk, aged twenty-three; and that of a girl, aged twelve, who had been a cripple from infancy, were alone remarkable for the amount of indigo blue which they yielded. In all these cases, the indigo blue was accompanied by the substance imparting to alcohol a purple colour, indirubine or urrhodine. The other specimens afforded much less, sometimes mere traces. all cases, however, in which the urine of the same individual was examined at different times, the amount of indigo blue obtained from it was found to vary exceedingly, it being sometimes considerable, and occasionally dwindling down to a mere trace. It was only very rarely, however, that none was found. In the case of the individual first referred to, the urine gave on one occasion not a trace, and this took place when he was engaged in performing labour, unusual for him both in its nature and amount. In Dr. Schunck's own case, as well as in that of his assistant, the amount varied most capriciously from a tolerable quantity to a mere trace, occasionally even none at all being obtained.

Several experiments with different kinds of diet, in order to ascertain the effect on the amount of indigo blue yielded by the urine, led to no very decisive results.

Of two samples of urine from patients with albuminuria, one gave a small quantity of indigo blue, the other not a trace. Several specimens of diabetic urine yielded it, and one of them a much larger quantity than had been obtained from any other specimen of human urine.

The urine of the horse and the cow, when tried in the same way as human urine, gave comparatively very large quantities of indigo blue, especially that of the horse.

CHAPTER XL.

PHENYLIC OR CARBOLIC ACID.

Formula: C12HO2.

History and Occurrence.

PHENYLIC acid was discovered, by Runge, in tar obtained by the distillation of coal. It is now an article of wholesale manufacture, and passes in commerce by the name of creosote. It occurs in castoreum together with salicine, both substances probably resulting from the barks of poplars and willows, the common food of the beaver (Wöhler). Städeler obtained it in small quantities from the urine of man, the horse, and the cow. After the internal or endermatic application of creosote, or substances containing it, such as tar, phenylic acid appears in the urine. Such urine frequently is black, or deposits a black precipitate of tarlike matter, a part of which may, perhaps, have some relation to indigo.

Mode of obtaining it pure.

a. From coal tar. Coal tar is subjected to distillation, and the products, which pass over at a temperature of from 150° to 200° C. (302° to 392° F.), are collected, mixed with a concentrated solution of potassa, in which phenylic acid is soluble. From this salt the acid is separated by means of hydrochloric acid, and by distillation over chloride of calcium is obtained anhydrous.

14 'Poggend. Annal.,' xxxi, p. 69; xxxii, p. 308.

2 Annal. d. Chem. und Pharm.,' lxvii, p. 360; lxxvii, p. 17.

3 See the cases by Dr. McLeod, Medical Gazette,' vol. ii, 1834-35, p. 599. Elliotson, Med.-Chir. Transact.,' vol. xix, p. 237. H. M. Hughes, Guy's Hospital Rep.,' 3d series, vol. ii, p. 52, where also several observations of Dr. Hermann Weber are quoted.

b. From urine of cows. Städeler obtained phenylic acid from this fluid by first removing hippuric acid in the usual way, with lime and hydrochloric acid. The mother-liquor he subjected to distillation, and the distillate to repeated rectification. The rectified fluid was distilled over hydrate of potassa, the residue was partly saturated with sulphuric acid, again distilled, the distillate rectified by chloride of sodium, and saturated with carbonate of soda. The oily matter thus separated was taken up with ether, the ether evaporated, and the residue again distilled over potassa; the rest of the acid was evolved from the potassa by the addition of bicarbonate of potassa. By continued fractional distillation almost pure phenylic acid was obtained.

c. From human urine, after the endermic administration of tar, or the internal use of creosote. In two cases of psoriasis, tar was rubbed over the whole surface. Three hours after the first inunction, the urine, which before had been clear and straw-yellow, became amber-yellow, and deposited uric acid in colourless plates. The urine which was passed after twelve hours was dark brownish-black, deposited a large sediment of coloured uric acid, and emitted the characteristic odour of tar. These peculiarities the urine retained during the entire course of the tar treatment.

When the brownish-black urine was left to spontaneous decomposition, which generally ensued on the fifth or sixth day, it assumed a dark-green (lauchgrün) colour, on the appearance of alkalescence, and then went through all the stages of ordinary decomposition.

The fact of the urine depositing uric acid so completely, that hydrochloric acid did not produce any further precipitate, suggested the probability of the presence of an abnormal acid in the urine. After the addition to the urine of some sulphuric acid, it was subjected to distillation, whereby an acid distillate was obtained, which emitted a strong odour of tar, was milky, but cleared up gradually, and deposited darkbrown drops, which were like creosote. A chip of pinewood, moistened with hydrochloric acid, and dipped into the clear watery fluid, gradually assumed a bluish-green colour. The addition of chloride of iron to this fluid produced a dark-brown mixture, and an excess of the chloride produced a brown adhering precipitate. Nitrate of silver produced a white precipitate, which, on the addition of ammonia, or simply on warming, was reduced to metallic silver. Neutral acetate of lead produced a white precipitate. When chlorine

1 Petters, W., Prager Vierteljahrschrift,' 1855, vol. iii, p. 126.