THE BILE. 63 



water-bath. Keep this for preparing an alcoholic solution 

 of the bile salts. 



(b.) Take some of the dry charcoal-bile mixture, and add 

 five times its volume of absolute alcohol. Cork the flask 

 or test-tube in which the mixture is placed. Shake up the 

 mixture from time to time, and after half an hour, filter. 

 To the filtrate add much ether, which gives a white precipi- 

 tate of the bile salts. If no water be present, sometimes the 

 bile salts are thrown down crystalline ; but not unfrequently 

 they go down merely as a milky opalescence, which quickly 

 forms resinous masses. It is best to allow the mixture to 

 stand for a day or two, to obtain the large glancing needles 

 which constitute Plattner's Crystallised Bile. 



3. Pettenkofer's Test for Bile Acids and Cholic Acid. 



(a.) Place some bile in a test-tube, add a drop or two of 

 syrup of cane sugar, and mix. Pour in concentrated sul- 

 phuric acid, and at the line of junction of the two fluids a 

 purple colour is obtained. 



The white deposit seen above the line of junction is pre- 

 cipitated bile acids. They are insoluble in water. 



(6.) Or, after mixing the syrup with the bile, add the 

 strong sulphuric acid drop by drop, mixing it thoroughly. 

 Heat gently, and the fluid becomes a deep purple colour. 

 Take care not to add too much syrup, and not to overheat 

 the tube. If the requisite amount of sulphuric acid be 

 added, the temperature becomes sufficiently high (70 C.) 

 without requiring to heat the tube. 



(c.) A better way of doing the test is as follows : After 

 mixing the bile and syrup, shake the mixture until the upper 

 part of the tube is filled with froth. Pour sulphuric acid 

 down the side, and a purple-red colour is struck in the 

 froth. 



(d.) It may also be done by mixing a few drops of bile in 

 a porcelain capsule, with a small crystal of cane sugar, and 

 after the sugar is dissolved, adding sulphuric acid drop by 

 drop. 



(e.) Strasburg's Modification (e.g., for bile in urine). To 

 the urine add a little syrup and mix. Dip filter-paper into 



