376 CHEMISTRY OF THE DIGESTIVE PROCESSES. 
rotate the plane of polarised light to the right ; in alcoholic solution the 
specific rotatory power for the acid is +20 o- 0, for the sodium salt -f25 0, 7 
(Hoppe-Seyler). The salts of the alkalies and alkaline earths are 
soluble both in water and in alcohol, those of the heavy metals are 
mostly much more insoluble in water, so that addition of salts of such 
metals as lead, copper, iron, or silver, causes precipitation of the corre- 
sponding glycocholates. The lead salt is soluble in rectified spirit, from 
which it is precipitated on the addition of water. The acid and its 
salts possess a peculiar taste, sweetish at first, but afterwards intensely 
bitter. 
Taurocholic acid (C 26 H 45 NS0 7 ), also a monobasic acid, is crystallisable 
with difficulty, forming fine deliquescent needles. It is very easily soluble 
in water, and also possesses the power of carrying glycocholic acid into 
solution when that acid is simultaneously present. It is exceedingly 
soluble in alcohol, but insoluble in ether. In solution it possesses a 
bitter-sweet taste, which is shared by its alkaline salts. The salts are 
generally easily soluble in water, and a solution of an alkaline tauro- 
cholate, unlike that of a glycocholate, is not precipitated by the usual 
salts of the heavy metals, such as copper sulphate, silver nitrate, or 
neutral lead acetate ; basic lead acetate does, however, precipitate it, and 
the compound so formed is soluble in boiling alcohol. 
Taurocholic acid is not nearly so stable a compound as glycocholic 
acid, it decomposes on boiling in aqueous solution, or in evaporating to 
dryness ; hence the dry pure acid has never been prepared or analysed, 
and its formula has been deduced from analogy with glycocholic acid, 
and from analyses of its more stable salts. Its solutions rotate the 
plane of polarisation to the right, like glycocholic acid. The specific 
rotation of the alcoholic solution of the sodium salt is +24° - 5. Potassium 
taurocholate occurs in the bile of many fishes ; it possesses the peculiar 
property of being completely thrown out of solution in water by the 
addition of solution of caustic potash, and so may be prepared by adding 
this reagent to an aqueous solution of an alkaline taurocholate. 
Analyses of this salt by Strecker 1 established its formula as 
C^H^KNSO;, and analyses of the sodium salt gave a corresponding 
result, from which it follows that the formula of taurocholic acid 
itself is C 2(! H 45 XS0 7 . 
Hyoglycocholic arid is an acid found in pig's bile, 2 which yields on decom- 
position glycocoll, like ordinary glycocholic acid, but an acid differing in 
composition and behaviour from ordinary cholalic acid (C 24 H 40 O ; ,), and 
called hyocholalic acid (C 25 H 40 O 4 ). This acid differs from cholalic acid in not 
being so easily crystallisable, and in having a difficultly soluble barium salt. 
Severin John J states that pig's bile contains, as principal bile salts, the sodium 
salts of two different hyoglycocholic acids, each of which yields on decomposi- 
tion glycocoll and a hyocholalic acid (a and ft). The two hyoglycocholic acids 
are distinguished by the different solubilities of their sodium salts in neutral 
salt solutions. The /3-salt is present in much greater quantity ; but the 
distinguishing character of pig's bile, that it is precipitated by saturation with 
various neutral salts, is not due to the /3- but to the adiyoglycocholic acid. 
1 Loc. cit. 
2 Strecker and Grundelach, Ann. d. Chem., Leipzig, 1847-9, Bd. lxii. S. 205 ; Bd. lxx. 
S. 179. 
3 Ztschr. f. physiol. Chem., Strassburg, 1887-9, Bd. xi. S. 417 ; Bd. xii. S. 512 ; 
Bd. xiii. S. 205. 
