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 +20'0, for the sodium salt 4-25 -? 

 (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 powqy 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 26 H 44 KNS0 7 , and analyses of the sodium salt gave a corresponding 

 result, from which it follows that the formula of taurocholic acid 

 itself is C 26 H 45 NS0 7 . 



Hyoylycoclwlic acid 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 5 ), and 

 called hyocholalic acid (C 25 H 40 4 ). This acid differs from cholalic acid in not 

 being so easily crystallisable, and in having a difficultly soluble barium salt. 

 Severin John 3 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 /?). 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 a-hyoglycocholic acid. 



1 Loc. cit. 



2 Strecker and Grundelacli, Ann. d. Chem., Leipzig, 1847-9, Bd. Ixii. S. 205 ; Bd. Ixx. 

 S. 179. 



3 Ztschr. f. physiol. Chem., Strassburg, 1887-9, Bd. xi. S. 417; Bd. xii. S. 512; 

 Bd. xiii. S. 205. 



