THE TAR ACIDS. 
§ 232 .] 
of phenol or cresol continually increasing, the amount of sulphates natur¬ 
ally in the urine (as estimated by simply acidifying with hydrochloric 
acid, and precipitating in the cold with chloride of barium) continually 
decreases, and may at last vanish, for all the sulphuric acid present is 
united with the phenol. On the other hand, the precipitate obtained 
by prolonged boiling of the strongly acidified urine, after filtering off 
any BaS0 4 thrown down in the cold, is ever increasing. 
Thus, a dog voided urine which contained in 100 c.c., -262 grm. of 
precipitable sulphuric acid, and -006 of organically combined sulphuric 
acid ; his back was now painted with carbolic acid, and the normal 
proportions were reversed, the precipitable sulphuric acid became 
•004 grm., while the organically combined was -190 in 100 c.c. In 
addition to phenyl-sulphuric acid, it is now sufficiently established 1 
that hydroquinone (^C 6 H 4 ^j^ (paradihydroxyl phenol) and pyro-cate- 
chin 
r xr OH\ 
6 4 OH/ 
(orthodihydroxyl phenol) are constant products of a 
portion of the phenol. The hydroquinone appears in the urine, in the 
first place, as the corresponding ether-sulphuric acid, which is colourless ; 
but a portion of it is set free, and this free hydroquinone (especially in 
alkaline urine) is quickly oxidised to a brownish product, and hence the 
peculiar colour of the urine. Out of dark-coloured carbolic acid urine the 
hydroquinone and its products of decomposition can be obtained by 
shaking with ether ; on separation of the ether, an extract is obtained, 
reducing alkaline silver solution, and developing quinone on warming 
with ferric chloride. 
To separate pyro-catechin, 200 c.c. of urine may be evaporated to an 
extract, the extract treated with strong alcohol, the alcoholic liquid 
evaporated, and the extract then treated with ether. On separation 
and evaporation of the ether a yellowish mass is left, from which the 
pyro-catechin may be extracted by washing with a small quantity of 
water. This solution will reduce silver solution in the cold, or, if treated 
with a few drops of ferric chloride solution, show a marked green colour, 
changing on being alkalised by a solution of sodic hydro-carbonate to 
violet, and then, on being acidified by acetic acid, changing back again to 
green. According to Thudichum, 2 the urine of men and dogs, after the 
ingestion of carbolic acid, contains a blue pigment. 
§ 232. The Action of Carbolic Acid considered physiologically.— 
Researches on animals have elucidated, in a great measure, the mode in 
which carbolic acid acts, and the general sequence of effects, but there is 
still much to be learnt. 
1 E. Baumann and C. Preuss, Zeitschrift f. phys. Chemie, iii. 156 ; Anleitung zur 
Ham-Analyse, W. F. Lobisch, Leipzig, 1881, pp. 142, ICO ; Schmiedeberg, Chem. 
Centrbl. (3), xiii. 598. 2 On the Pathology of the Urine , Lond., 1877, p. 198. 
