558 PHYSIOLOGICAL CHEMISTRY 



consideration for the clinician inasmuch as urines which contain acetone and aceto- 

 acetic acid are generally those from which the ammonia data are also desired. The 

 procedure for the combination method is as follows: Arrange the ammonia appar- 

 atus as usual (see page 519), and to the aerometer of the ammonia apparatus attach 

 the acetone apparatus set up as described above. Regulate the air current with 

 special reference to the determination of acetone and at the end of 20-25 minutes 

 disconnect the acetone apparatus and complete the determination of the acetone 

 as just described. The air current is not interrupted, and after having run one 

 and one-half hours the ammonia apparatus is detached and the ammonia determina- 

 tion completed as described on page 519. 



If data regarding acetoacetic acid are desired, the result obtained by Folin's 

 method may be subtracted from the result obtained by the Van Slyke method 

 for acetone and acetoacetic acid. Under all conditions the determination of 

 acetone should be as expeditious as possible. This is essential, not only because 

 of the fact that any acetoacetic acid present in the urine will become transformed 

 into acetone, but also because of the rapid spontaneous decomposition of the alka- 

 line hypoiodite solution used in the determination of the acetone. It has been 

 claimed that alkaline hypoiodite solutions are almost completely converted into 

 iodate solutions in one-half hour. Folin states, however, that the transformation 

 is not so rapid as this, but he nevertheless emphasizes the necessity of rapidity of 

 manipulation. At the same time it should be remembered that the air current 

 must not be as rapid as for ammonia, inasmuch as the alkaline hypoiodite solution 

 will not absorb all the acetone under those conditions. 



Indican 



Ellinger's Method. Principle. This method for the quantitative 

 determination of indican is based upon the principle underlying Jaffe's 

 qualitative test for indican. The urine after removal of interfering 

 substances with basic lead acetate is treated with Obermayer's reagent 

 to oxidize the indican to indigo. The indigo is extracted with chloro- 

 form, the chloroform evaporated off and the residue titrated with 

 potassium permanganate. The method is not very accurate but is as 

 satisfactory as any. 



Procedure. To 50 c.c. of urine 1 in a small beaker or casserole add 5 c.c. 

 of basic lead acetate solution, 2 mi* thoroughly, and filter. Transfer 40 c.c. of 

 the filtrate to a separatory funnel, add an equal volume of Obermayer's reagent 

 (see page 405) and 20 c.c. of chloroform, and extract in the usual manner. This 

 extraction with chloroform should be repeated until the chloroform solution 

 remains colorless. Shake up the combined chloroform extracts two or three 

 times with distilled water in a separating funnel and complete the purification 

 by extracting with very dilute sodium hydroxide (i :iooo). Remove all traces 

 of alkali by washing with water. Now filter the combined chloroform extracts 

 through a dry filter paper into a dry Erlenmeyer flask. Distil off the chloro- 

 form, heat the residue on a boiling water-bath for five minutes in the open 



1 If the urine under examination is neutral or alkaline in reaction it may .be made 

 faintly acid with acetic acid before adding the basic lead acetate. 



2 For preparation of basic lead acetate solution see p. 629. 



