

212 THE BILE. 



found in appreciable quantity. Other tests are therefore necessary in 

 investigations for the biliary salts proper. 



The ordinary characters of the biliary salts are that they are soluble 

 in water and in absolute alcohol, and insoluble in ether ; and that they 

 will gradually crystallize in the form of radiating needles, if precipitated 

 from their alcoholic solution by the addition of ether in excess. Fur- 

 thermore, they are both precipitable from their watery solutions by the 

 tribasic lead acetate, while the sodium glycocholate is also precipitable 

 by the neutral acetate of the same metal. 



Pettenkofer's Test. The biliary salts accordingly, when in consider- 

 able quantity, may be recognized by the above-named properties ; but 

 when present in smaller proportions they are to be detected by the 

 reaction known as *' Pettenkofer' l s test." This consists in the production 

 of a red color, changing to a purple or violet, on the addition of cane 

 sugar and sulphuric acid. The test is applied in the following way : 

 One part of^cjine sugar is dissolved in four parts of water. Of this 

 saccharine liquid, one drop is added to each cubic centimetre of the solu- 

 tion of biliary salts. The sugar should not be used in larger quantity, 

 because it might in that case give a perceptible brown tinge under the 

 action of sulphuric acid and heat. The admixture of the sugar pro- 

 duces no visible change in the solution of biliary salts. On adding a 

 few drops of pure sulphuric acid, the biliary acids are decomposed, form- 

 ing cholic acid. If the biliary salts were originally present in the solu- 

 tion in a proportion of not more than one part in 500, the fluid remains 

 clear ; if in larger quantity, the cholic acid is precipitated, forming a 

 whitish turbidity. This turbidity is again cleared up on the continued 

 addition of sulphuric acid ; and in the course of a few minutes, a cherry- 

 red color appears, which rapidly changes to a violet, and subsequently, 

 if the biliary salts be present in the proportion of one part in 500, or 

 over, to a deep rich purple. In very dilute solutions, the violet or purple 

 color may not be distinctly visible before the end of an hour. 



The precautions necessary to observe in using this test are as follows : 

 First, the liquid to be examined should be free from other organic sub- 

 stances, particularly albuminous and coloring matters, which might 

 themselves cause discoloration of the mixture. For this purpose, the 

 suspected fluid should always be first evaporated to dryness, the dry 

 residue extracted with absolute alcohol, the alcoholic solution decolorized, 

 if necessary, with animal charcoal, then precipitated with ether in excess, 

 and the ether precipitate finally dissolved in water. This gives a clear, 

 colorless solution, free from other organic contamination. Secondly, 

 as the liquid becomes heated by the liberal admixture of sulphuric acid 

 with the watery solution, its temperature should not be allowed to rise 

 above 70 (158F.) nor to fall much below this point. The test-tube 

 may therefore be cooled by occasionally moistening it in cold water. 

 Thirdly, the addition of the sulphuric acid should be made slowly, and 

 should be stopped as soon as a red tint begins to show itself, the mix- 



