CHAP. VIII.] METHODS FOR THE ANALYSIS OF BILE. 395 



and evaporating the ethereal "solution to dryness. The aqueous 

 solution of barium cholalate, &c. is concentrated to a small volume, 

 the solution not being filtered x from the precipitate which separates; 

 ether is added to it and then dilute hydrochloric acid, which throws 

 down cholalic acid. The liquid is allowed, however, to remain 

 exposed to the air for some days so as to permit of the evaporation 

 of the ether. The cholalic acid which has then separated is collected 

 on a weighed filter, washed, dried at 120 C. and weighed. If 

 desired, the filtrate may be freed-from barium by means of ammonium 

 carbonate and the amount of ammonia and the sulphur in it 

 (representing the taurine) determined. 



Knowing the amount of sulphur, we may calculate firstly the 

 amount of taurocholic acid which it represents, and secondly the 

 amount of cholalic acid which would result from its decomposition, 

 seeing that 100 parts of taurocholic acid, when decomposed, yield 

 72'22 parts of cholalic acid. If we deduct this quantity of cholalic 

 acid from the total amount which is obtained as a product of the 

 decomposition of the mixed bile acids, we naturally find the amount 

 of cholalic acid which must have existed as glykocholic acid, seeing 

 that 100 parts of cholalic acid represent 113'98 parts of glykocholic 

 acid. 



The determination of the rotatory power of the alcoholic solution 

 previously recommended serves to control the results obtained by 

 the method just described. 



If a be the observed rotation expressed in degrees for the line D 

 of a column of the solution 1 decimeter thick, and m the amount of 

 taurocholic acid calculated from the weight of the barium sulphate 

 (the Sp. Rot. (a)D of sodium taurocholate in alcoholic solution being 

 = 4- 25'3 and of sodium glykocholate + 27 0> 6), then the amount x of 

 glykocholic acid in the fluid will be found by the following equa- 

 tion : 



100. a -m. 25-3 



Determinations of the Colouring Matters of the Bile. 



These are only possible by the method of spectro-photometry. 

 As we know the optical constants, of which a knowledge is needed, 

 both of bilirubin and biliverdin, it is perfectly possible to determine 

 the absolute and relative amounts of bilirubin and biliverdin in a 

 bile containing one or other or both of these constituents. The 

 methods of spectro-photometry will be described in all detail in the 

 2nd edition of Vol. I. 



