METHOD OF ANALYSING IT. 73 



extracted with anhydrous ether, a process requiring much time, 

 because we cannot pulverise it like the residues of other animal 

 fluids, in order to submit to further analysis a newly dried and 

 weighed quantity. The etherial extract contains fat, and not un- 

 frequently also a little of the resinous biliary matters, which may 

 be separated from the fat by aqueous spirit. The residue insoluble 

 in ether, which contains the essential constituents of the bile, must 

 be dissolved in absolute alcohol; we must then remove the greater 

 part of the alcohol by distillation or evaporation, and treat the 

 concentrated fluid with ether as long as any turbidity is observable ; 

 there then generally only remains a very little alkali in combination 

 with a fatty acid, and some chloride of sodium in the ethereo- 

 alcoholic fluid ; the fluid with its precipitate must, however, stand 

 for a considerable time in a cool place, because the alkaline glyco- 

 cholate only separates very slowly. The salts of the biliary acids 

 which are thus separated, are unfortunately always mixed with 

 bile-pigment, from which they can only rarely be separated by the 

 addition of chloride of calcium to their alcoholic solution (namely, 

 when the pigment consists of true cholepyrrhin). By dissolving 

 in alcohol a portion of the mixed giycocholates and taurocho- 

 lates precipitated by ether, and by adding sulphuric acid to the 

 solution, we can determine the quantity of the soda or potash in 

 combination with these salts and with pigment, and we can ascertain 

 whether or not ammonia be present. Unfortunately the determi- 

 nation of the alkali in this way is not strictly accurate, since a 

 little chloride of sodium and soda in combination with a fatty acid, 

 always occur in the precipitate thrown down by the ether, and 

 thus contribute their alkali to that with which the biliary acids 

 were combined. An exact separation of the taurocholic and glyco- 

 cholic acids is impossible (as indeed is obvious, from what has 

 been stated in vol. i. p. 232) ; consequently the best method of 

 calculating the amount of the biliary acid yielding taurine, is by 

 determining the quantity of sulphur in the biliary salts* which 

 have been precipitated by ether; for this purpose we oxidise a 

 weighed portion of them with potash or soda and nitre in the dry 

 way, and determine the sulphuric acid that is formed. As, even 

 if sulphates had been present, no sulphuric acid could have got 

 into the alcoholic extract, it is obvious that all the sulphuric acid 

 that is found, must have been derived from the sulphur which was 

 in combination with organic matter; and taurocholic acid is the 

 only sulphurous substance contained in the alcoholic extract. 

 * [The alkaline taurocliolates and giycocholates. G. E. *>'] 



