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PHYSIOLOGICAL CHEMISTRY. 



glycocholic acid is extremely difficult, hence in preparing it, it is best to 

 start with a bile which contains essentially only the one salt. Dog's bile 

 should therefore be employed. Treat it as described for the mixed salts, 

 and decompose finally with dilute sulphuric acid in presence of ether. 



Preparation of Cholalic Acid. Dissolve 200 grams of barium hydroxide 

 in 6 liters of water. In this solution saponify 50 gm. of glycocholic acid, 

 by boiling ten to twenty hours, replacing the water lost by evaporation. 

 Filter hot and to the cooled liquid add enough hydrochloric acid to decom- 

 pose the barium salt. The cholalic acid separates in the form of a granu- 

 lar precipitate. Wash with water and crystallize from hot, strong alcohol. 



Optical Properties of These Acids. The three acids and their sodium 

 salts are characterized by rather strong rotating power, which under some 

 circumstances may be used for measurement or identification. The fol- 

 lowing specific rotations have been found: 



CHEMICAL TEST FOR THE BILE SALTS. The three acids are characterized 

 by giving a certain reaction with furfuraldehyde, or sugar yielding fur- 

 furaldehyde, in presence of acid. The test is commonly made by adding 

 to a dilute solution of the salts, say 5 cubic centimeters, a few drops of 

 a dilute cane sugar solution and strong sulphuric acid in volume about 

 half that of the mixture. Let the acid flow down the side of the test- 

 tube so as to form a layer below the lighter liquid. A deep purple band 

 appears at the line of contact. On slowly mixing the liquids in the test- 

 tube the color becomes purple throughout. In this test any excess of 

 sugar must be avoided. 



With a trace of pure furfuraldehyde in place of sugar the reaction is 

 sharper, but certain proportions must be observed. A good mixture is 

 i cubic centimeter of weak alcoholic solution of the bile acid, i drop of 

 O.I per cent furfuraldehyde solution and I cubic centimeter of strong 

 sulphuric acid. The original test was devised by Pettenkofer; later it 

 was recognized that the reaction belongs to the group of " furfurol " reac- 

 tions, and the aldehyde was recommended in place of the sugar. The 

 test cannot be used with bile directly because of the presence of other 

 substances, which would give a strong color with the sulphuric acid. 



Preparation of Taurin. Use several hundred cubic centimeters of ox 

 bile. Add to it an excess of strong hydrochloric acid, about one-third 

 of the volume of the bile, and boil on the water-bath. A resinous mass 

 separates and when this becomes stringy enough to solidify, when a little 



