URINE. 333 



urine under examination to one-third or one- fourth of its original 

 volume in an evaporating dish at a gentle heat. Acidify the resi- 

 due with a few drops of concentrated hydrochloric acid, add suffi- 

 cient plaster of Paris to make a thick paste and allow the mixture 

 to stand until it begins to " set." It should now be stirred and 

 broken up in the dish by means of a stirring rod with a blunt end. 

 Extract the porous meal thus produced twice with ether by stirring 

 and decantation. Any /3-ox)fbutyric acid present will be extracted 

 by the ether. Evaporate the ether extract spontaneously or on a 

 water-bath, dissolve the residue in water and neutralize it with 

 barium carbonate. To five to ten c.c. of this neutral fluid in a test- 

 tube add two to three drops of ordinary commercial acid hydrogen 

 peroxide. Mix by shaking and add a few drops of Black's reagent. 1 

 Permit the tube to stand and note the gradual development of a 

 rose color which increases to its maximum intensity and then 

 gradually fades. 2 



In carrying out the test care should be taken to see that the 

 solution is cold and approximately neutral and that a large excess 

 of hydrogen peroxide and Black's reagent are not added. In case 

 but little /3-oxybutyric acid is present the color will fail to appear or 

 will be but transitory if the oxidizing agents are added in too great 

 excess. It is preferable to add a few drops of the reagent and at 

 intervals of a few minutes repeat the process until the color under- 

 goes no further increase in intensity. One part of /?-oxybutyric 

 acid in 10,000 parts of the solution may be detected by this test. 



2. Polariscopic Examination. Subject some of the urine (free 

 from protein) to the ordinary fermentation test (see page 313). 

 This will remove dextrose and laevulose, which would interfere with 

 the polariscopic test. Now examine the fermented fluid in the 

 polariscope and if it is laevorotatory the presence of /3-oxybutyric 

 acid is indicated. This test is not absolutely reliable, however, 

 since conjugate glycuronates are also Isevorotatory after fermenta- 

 tion. 



3. Kulz's Test. Evaporate the urine, after fermenting it as 

 indicated in the last test, to a syrup, add an equal volume of con- 

 centrated sulphuric acid and distil the mixture directly without cool- 

 ing. Under these conditions a-crotonic acid is formed and is 

 present in the distillate. Allow the distillate to cool slowly and 



1 Made by dissolving five grams of ferric chloride and 0.4 gram of ferrous 

 chloride in 100 c.c. of water. 



"This disappearance of color is due to the further oxidation of the diacetic 

 acid. 



