538 PHYSIOLOGICAL CHEMISTRY 



Interpretation. See page 534. 



Acetone 



Folin's Method. Principle. The preformed acetone is aspirated 

 from the urine mixture at room temperature to prevent decomposition 

 of acetoacetic acid. The acetone is collected in alkaline hypoiodite 

 solution as in the Folin-Hart method (page 533). lodoform is formed 

 quantitatively and the excess of iodine is titrated with sodium thio- 

 sulphate. 



Procedure. The same type of apparatus is used in this method as that 

 described in Folin's method for the determination of ammonia (see page 499). 

 Introduce 20-25 c.c. of the urine under examination into the aerometer cylinder 

 and add 10 drops of 10 per cent phosphoric acid, 1 8-10 grams of sodium chloride, 2 

 and a little petroleum. Introduce into an absorption flask, 3 such as is used in the 

 ammonia determination (see page 499), 150 c.c. of water, 10 c.c. of a 40 per cent 

 solution of potassium hydroxide, and an excess of a N/io iodine solution. Con- 

 nect the flask with the aerometer cylinder, attach a Chapman pump, and permit 

 an air current, slightly less rapid than that used for the determination of ammonia, 

 to be drawn through the solution for 20-25 minutes. All of the acetone will, at 

 this point, have been converted into iodoform in the absorption flask. Add 

 10 c.c. of concentrated hydrochloric acid (a volume equivalent to that of the strong 

 alkali originally added), to the contents of the latter and titrate the excess of 

 iodine by means of N/io sodium thiosulphate solution and starch, as in the Mes- 

 singer-Huppert method (see page 535). 



Folin has further made suggestions regarding the simultaneous determination 

 of acetone and ammonia by the use of the same air current. 4 This is an important 

 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 499), 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 500. 



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

 method may be subtracted from the result obtained by the Messinger-Huppert 

 method (see page 535), inasmuch as the latter method determines both 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 



1 Oxalic acid (0.20.3 gram) may be substituted if desired. 



2 Acetone is insoluble in a saturated solution of sodium chloride. 



3 Folin's improved absorption tube (see Fig. 128, p. 500) should be used in this connec- 

 tion inasmuch as the original type embracing the use of a rubber stopper is unsatisfactory 

 because of the solvent action of alkaline hypoiodite on rubber. 



4 These determinations may even be made on the same sample of urine if the sample is 

 too small for the double determination. 



