THE BILE ACIDS. 377 
The two hyocholalic acids show analogous differences to the two hyoglycocholic 
acids. The formula of a-hyoglycocholic acid is C._, 7 H 4r >X< ) SI that of /3-hyo- 
glycocholic acid is C II X< >-,. 
Taurochenocholic acid, 1 the principal bile acid of goose bile, has the 
formula C^H^NSOg, has not been crystallised, and is soluble in water and 
alcohol. From this acid Heintz and Wislicenus - prepared chenocholic acid 
(C. 27 H 44 4 ) ; this is itself crystallisable with difficulty, but yields a barium salt, 
which is insoluble in water and can easily be obtained in a crystalline form. 
Pettenkofers test for bile acids. 3 — When bile is gently warmed with 
concentrated sulphuric arid and cane-sugar, a beautiful purple or 
purplish-red colour develops, becoming deeper on standing. The colour 
is due to an interaction between the bile salts, or cholalic acid, and a 
substance called furfurol or furfuraldehyde developed by the action of 
the strong sulphuric acid on the cane-sugar; 4 hence the test may 
be more satisfactorily carried out where only traces of bile salts are 
suspected, by using a solution of furfurol (1 per 1000) instead of cane- 
sugar. 
To carry out the test in the ordinary manner, add to a drop or two of the 
bile, or fluid suspected of containing bile acids, a drop of strong sulphuric 
acid, taking care that any great rise in temperature does not occur; spread the 
mixture out in a thin film in a porcelain capsule, and either add a drop of a 
10 per cent, solution or a small crystal of cane-sugar ; if the violet colour does 
not appear at once, warm very gently. To carry out the test with furfurol, one 
drop of a solution of furfurol (1 per 1000) is added to 1 c.c. of an alcoholic 
solution of bile salts, and 1 c.c. of concentrated sulphuric acid is added 
cautiously to this, so as not to overheat. In this manner ^V - ;ro of a milligramme 
of cholalic acid may be detected. 5 
The test with sugar may be easily spoiled by overheating or when 
too much sugar is used, which favours carbonisation. The presence of 
sulphurous acids or nitrous fumes in the sulphuric acid is also unfavour- 
able to the reaction. Strong phosphoric acid may be used instead of 
sulphuric acid. 
Many other substances give a similar reaction. Pettenkofer himself 
was aware that proteids gave a similar colour, though much less easily. 
By subsequent observers 6 a large number of substances giving colour re- 
actions with furfurol have been described ; amongst these many phenols 
and aromatic bases are included, some of which are also found in 
the urine, v. Udranszky 7 gives a list of over forty substances which 
give colour reactions with furfurol, but none except a-naphthol show 
the reaction with the same delicacy as the bile salts. That the 
coloured substance so produced is not in all cases the same, is shown 
by the fact that some possess no absorption spectrum, and that the 
spectra of the others differ from one another. In this way the 
spectrum of the colour given by the bile salts may be distinguished 
1 Marsson, Arch. d. Pharrn., Bd. lvii. S. 138, 
2 Ann. d. Phijs. u. Chan., Leipzig, 1S59, Bd. cviii. S. 547. 
3 Ann. d. Chem., Leipzig, 1S44, Bd. Hi. S. 90. 
4 Mylius, Ztschr. f. physiol. Chem., Strassburg, 1887, Bd. xi. S. 492. 
5 v. Udrauszky, ibid., 1888, Bd. xii. S. 355. 
6 Baeyer, Per. d. deutsch. chem. Gesellsch., Berlin, 1872, Bd. v. S. 26 ; Stenhouse, 
Ann. d. Chem., Leipzig, 1870, Bd. clvi. S. 197 ; Schiff, ibid., Bd. cci. S. 355. 
7 Loc. cit. Drechsel, Journ. f. prakt. Chem., Leipzig, Bd. xxvii. S. 424. 
