212 TAUKOCHOLIC ACID. 



This is next washed, suspended in alcohol, and decomposed by 

 sulphuretted hydrogen. After removal of the sulphide of lead 

 by filtration the alcoholic filtrate is concentrated and the tauro- 

 cholic acid precipitated by an excess of ether. This yields a sirupy 

 mass which may become partly crystalline on standing : the 

 crystals at once deliquesce on exposure to the air. 1 As dog-bile 

 is not readily obtainable in large quantity at any one time, it may 

 be desirable sometimes to obtain taurocholic acid from the mother 

 liquor left in the preparation of glycocholic acid. The separation 

 is effected by the addition of a little ammonia and normal lead 

 acetate. This precipitates both glycocholic and cholalic acid, but 

 not taurocholic. After the removal of this precipitate the tauro- 

 cholic acid is prepared as already described by the addition of 

 basic lead acetate to the filtrate. 



This acid, as already stated, is extremely soluble in water and 

 in alcohol, but not in ether ; so also are its salts with the excep- 

 tion of the one formed on the addition of basic lead acetate in 

 presence of ammonia, which is insoluble in water and in alcohol. 

 The acid and its salts are dextro-rotatory ; for the sodium salt 

 in alcoholic solution (a) D = -f 24'5. If dissolved in water the 

 rotatory power is less, and in this respect it resembles glycocholic 

 acid. 



When hydrolised it readily takes up a molecule of water and is 

 decomposed into taurin and cholalic acid : 



Taurin Cholalic acid. 



C 26 H 45 NS0 7 + H 2 = NH 2 . CH 2 . CH 2 . S0 2 OH + C 24 H 40 5 . 



This decomposition may, as in the case of glycocholic acid, be 

 brought about by the action of dilute acids or alkalis, but even 

 mere boiling of an aqueous solution of the acid also suffices, 

 a fact which demonstrates how unstable a substance it is, 

 both absolutely and as compared with glycocholic acid. Tau- 

 rocholic acid has not as yet been observed in the urine in 

 icterus, but since cholalic acid does occur together with glyco- 

 cholic acid, it is probable that the non-appearance of taurocholic 

 acid is due to its decomposition before excretion as a result of its 

 instability. 



Taurocholic acid possesses a remarkable power of effecting the 

 complete precipitation of ordinary proteids from their solutions, 

 whereas peptones if present at the same time remain unprecipi- 

 tated. This is possibly of some not inconsiderable importance in 

 connection with the changes which proteids undergo in the small 

 intestine, since it leads to the retention of the peptones in a state 

 of solution and hence facilitates their absorption, while the less 

 completely altered proteids are precipitated and thus further ex- 



1 Parke, Hoppe-Seyler's Med.-chem. Unters. Hft. 1. (1866), S. 160. 



