URINE 541 



the whole has been added. 1 Should the liquid become markedly green the 

 bichromate must be added at correspondingly shorter intervals and in amount 

 sufficient to maintain a slight red-yellow color of the chromic acid which may be 

 detected even in the presence of the green. Continue the distillation with moder- 

 ate boiling for from two to three hours. The distillate which should be collected 

 in a liter flask to avoid transference is again distilled for about 20 minutes 

 after adding 10 c.c. of 10 per cent sodium hydroxide and 25 c.c. of 3 per cent 

 hydrogen peroxide. The flask must be heated cautiously until the peroxide has 

 been decomposed. This final distillate is titrated with standard iodine and 

 thiosulphate in the usual manner (see page 536) and the result expressed as 

 hydroxybutyric acid. One c.c. of N/io iodine solution is equivalent to 1.736 

 mg. of hydroxybutyric acid. One c.c. of the 1.035 N/io iodine which is recom- 

 mended for acetone titrations is equivalent to 1.793 m S- of hydroxybutyric acid. 

 About 10 per cent should be added to the results for /3-hydroxybutyric acid as 

 obtained by this method as the yield of acetone is only about 90 per cent of 

 the theoretical. This error appears to be practically constant, so that satisfactory 

 results may be obtained by correction. 



Interpretation. /3-Hydroxybutyric acid may occur in normal human 

 urine to the extent of 20-30 mg. per day. In fasting or on a carbo- 

 hydrate-free diet very large amounts may be excreted (up to 20 grams 

 per day). In severe diabetes mellitus the largest amounts are found. 

 Excretions of 50 or even 100 grams or over per day have been noted. 

 It is always present in the urine when large amounts of acetone are 

 present. In severe diabetes it is usually the most abundant of the 

 acetone bodies making up from 60-80 per cent of the total. The 

 ratio is, however, by no means constant and it should be borne in mind 

 that in rare cases large amounts of ^-hydroxybutyric acid may be 

 eliminated although the acetone excretion is very low. (See Acetone 

 and Acetoacetic Acid.) 



2. Nephelometric Methods for Acetone, Acetoacetic Acid, and 

 0-Hydroxybutyric Acid. Folin and Denis 2 have suggested nephelo- 

 metric methods for the determination of the acetone bodies in urine. 

 The methods are similar to those used by Marriott for blood analysis t 

 (see Chapter XVI) but the air current is used instead of distillation. 



^-Hydroxybutyric Acid 



i. Black's Method. Principle. The urine is mixed with plaster 

 of Paris to form a coarse meal and extracted with ether to obtain 

 the hydroxybutyric acid which is then determined by means of the 

 polariscope. 



1 From 0.5 gram to i gram of bichromate will usually be sufficient, and not more than 

 i gram should be added unless the liquid turns green indicating a great reduction to 

 chromium sulphate. Very rarely 2 or 3 grams of bichromate may be necessary, especially 

 if the sugar has not been completely removed. 



2 Folin and Denis: Jour. Biol. Chem., 18, 263, 1914. 



