33 PHYSIOLOGICAL CHEMISTRY. 



upon this acid solution. At the zone of contact a blackish-gray 

 ring of precipitated mercuric sulphide, HgS, will form. Alde- 

 hyde also responds to this test. Aldehyde, however, has never 

 been detected in the urine and could only be present in this instance 

 if the acidified urine was distilled too far. 



6. Taylor's Test. To 10 c.c. of the urine or distillate in a test- 

 tube add a few drops of a freshly prepared aqueous solution of 

 sodium nitroprusside and stratify concentrated ammonium hydrox- 

 ide upon the mixture. The production of a magenta color at the 

 point of contact indicates the presence of acetone in the urine or 

 distillate under examination. Normal urine yields an orange-red 

 color when subjected to this technique. 



CH 3 



,.{= 



CH> 



DIACETIC ACID, = 



COOH. 



Diacetic or acetoacetic acid occurs in the urine only under patho- 

 logical conditions and is rarely found except associated with acetone. 

 It is formed from /3-oxybutyric acid, another of the acetone bodies, 

 and upon decomposition yields acetone and carbon dioxide. Dia- 

 ceturia occurs ordinarily under the same conditions as the patholog- 

 ical acetonuria, i. e. } in fevers, diabetes, etc. (see p. 328). If very 

 little diacetic acid is formed it may all be transformed into acetone, 

 whereas if a larger quantity is produced both acetone and diacetic 

 acid may be present in the urine. Diaceturia is most frequently 

 observed in children, especially accompanying fevers and digestive 

 disorders ; it is perhaps less frequently observed in adults, but when 

 present, particularly in fevers and diabetes, it is frequently followed 

 by fatal coma. 



Diacetic acid is a colorless liquid which is miscible with water, 

 alcohol, and ether, in all proportions. It differs from acetone in 

 giving a violet-red or Bordeaux-red color with a dilute solution of 

 ferric chloride. 



EXPERIMENTS. 



i. Gerhardt's Test. To 5 c.c. of urine in a test-tube add ferric 

 chloride solution, drop by drop, until no more precipitate forms. 

 In the presence of diacetic acid a Bordeaux-red color is produced; 

 this color may be somewhat masked by the precipitate of ferric 

 phosphate, in which case the fluid should be filtered. 



