TAUROCHOLIC ACID. 233 



ammonia. This precipitate must be decomposed with carbonate 

 of soda, and we must extract the solid residue of the filtered fluid 

 with alcohol. On the addition of ether to the alcoholic solution, a 

 tolerably pure taurocholate of soda is immediately precipitated in 

 the form of a resinous, semifluid, yellow mass. If this be dissolved 

 in a small quantity of water, and all that is precipitable by acetate 

 of silver be thrown down, and if the fluid after filtration be pre- 

 cipitated with basic acetate of lead, and the precipitate, after being 

 thoroughly diffused in a little water, be treated with sulphuretted 

 hydrogen, we obtain tolerably pure taurocholic acid after evapo- 

 rating in vacua. 



Tests. No great weight can be attached to any of the differ- 

 ences in the reaction of the salts of glycocholic and taurocholic 

 acids, when the quantity of the substance presented to us for exa- 

 mination is very small. If, however, we have sufficient material, 

 we must obtain the acids from the alcoholic extract with precisely 

 the same precautions as we have indicated in the preceding pages 

 in reference to each of these acids ; from the ratio of the precipi- 

 tate caused by the sugar of lead to that caused by the acetate of 

 lead, we must draw our conclusions regarding the relative quan- 

 tities of the two acids, and then, by treating the alcoholic solution 

 of the soda- salt with ether, we can determine this point with cer- 

 tainty ; indeed, we shall always be most decisively convinced of 

 the presence of taurocholic acid by the exhibition of the taurine, 

 which, even if obtained in only very small quantities, may be 

 recognised with certainty by crystallometric examination under the 

 microscope. Unfortunately, however, the quantities of taurine are 

 so minute, unless when we are acting directly on bile, that it cannot 

 be distinguished and recognised with certainty either by the above 

 means or by its relation towards nitrate of silver and other metallic 

 salts. Nothing further remains for us but to determine the pre- 

 sence of sulphur; having ascertained by Pettenkofer's test that 

 biliary matter is present in the substance under examination, we 

 must extract the spirituous extract with cold absolute alcohol, con- 

 centrate this solution, and treat it with ether. A precipitate then 

 falls, which cannot contain any other known sulphurous substance, 

 and which we must fuse and deflagrate with nitrate of potash and 

 caustic potash free from sulphuric acid; if sulphuric acid be found 

 in the residue, we may regard the presence of taurocholic acid as 

 almost certain. 



Unfortunately, substances in which it is of interest to detect 

 small quantities of taurocholic acid, are seldom obtained in a state 



