CHEMICAL BASIS OF THE ANIMAL BODY. 197 



acid 1 . When introduced into the animal body the three isomeric 

 kresols undergo distinctly different oxidational changes 2 . 



Reactions. On the addition of an excess of bromine water to its 

 solutions parakresol yields a brominated derivative, but the compound 

 is only obtained in a separate and crystalline form after prolonged 

 standing, differing characteristically from the analogous compound 

 of phenol which under similar circumstances is formed rapidly. It 

 yields a reddish yellow colouration with potassium nitroprusside 

 and caustic potash, which turns bright pink on the addition of an 

 excess of acetic acid 3 . Aceton gives a similar reaction. With furfurol 

 and sulphuric acid the reaction is closely similar to that which phenol 

 gives 4 . 



7. Pyrocatechin. C 6 H 4 (OH) 2 . Orthodioxybenzol. 



This substance occurs, in small amounts in human urine united 

 with sulphuric acid as a mono-ethereal compound OH . C 6 H 4 . O . S0 2 OH. 

 It is more plentifully present in the urine of herbivora, especially of the 

 horse, and is largely increased in amount by the administration of 

 benzol or phenol 5 . It is also stated to occur in cerebrospinal fluid 6 . 

 When present in urine it (together with hydrochinon) confers on this 

 excretion, especially if alkaline, the property of turning successively 

 greenish, brown and finally dark-brown or almost black on exposure to the 

 air, and of readily reducing solutions of metallic salts, a fact to be taken 

 into account when dealing with the presence or absence of sugar in the 

 urine. Solutions of pyrocatechin turn emerald green on the addition 

 of a few drops of very dilute solution of ferric chloride, avoiding all 

 excess of the reagent. If the green solution is now acidulated with 

 tartaric acid, it turns violet on the subsequent addition of a little 

 ammonia and purplish-red on the addition of excess. The green 

 colour may be restored by excess of acetic acid 7 . It may be distin- 

 guished from hydrochinon by yielding a precipitate with normal 

 acetate of lead which is soluble in acetic acid, whereas the latter 



1 Baumann u. Brieger; Ibid. Bd. m. (1879), S. 149. Baumann, Ibid. iv. S. 

 304. For the detection and separation of the kresols and phenol see Baumann 

 u. Brieger, Ber. d. d. chem. Gesell. Bd. xn. (1879), S. 804. Baumann, Zt. f. 

 physiol. Chem. Bd. vi. (1882), S. 183. Brieger, Ibid. vm. (1883), S. 311. 



2 Preusse, Ibid. Bd. v. (1881), S. 57. 



3 v. Jaksch., Zt.f. Uin. Med. Bd. vm. (1884), S. 130. 



4 Udranszky, cit. (sub. phenol). 



5 See Bauiriann, Pfliiger's Arch. Bd. xn. (1876), S. 63, Baumann u. Herter, Zt. 

 f. physiol. Chem. Bd. i. (1877), S. 248, Baumann u. Preusse, Ibid. Bd. m. (1879), S. 



156. Brieger, Arch. f. physiol. Jahrg. 1879, Suppl-Bd. S. 61. Nencki u. Giacosa, 

 Zt. f. physiol. Chem. Bd. iv. (1880), S. 325. Schmiedeberg, Arch. f. exp. Path. u. 

 Pharm. Bd. xiv. (1881), S. 288. 



Halliburton, Jl. of Physiol. Vol. x. (1889), p. 247. 



7 Ebstein u. Miiller, Virchow's Arch. Bd. LXV. (1875), S. 394. See also Jacque 

 min, Rev. Med. de VEst. T. vm. (1877), p. 90. 



