URINE 415 



examination, and heat the mixture to boiling. Now introduce 10 c.c. of a 3 per 

 cent solution of potassium hydroxide and gently shake the tube and contents. If 

 the urine under examination contains glucose the liquid in the tube will assume a 

 red color. One per cent glucose yields an immediate color whereas 0.05 per cent 

 yields the color only after the lapse of a period of one-half hour from the time the 

 alkali is added. If the color appears after the 30-minute interval the color change 

 is without significance inasmuch as sugar-free urines will respond thus. The reac- 

 tion is given by all aldehydes and therefore the test cannot be safely employed in 

 testing urines preserved by formaldehyde. Albumin does not interfere with the 

 test. 



4. Bottu's Test. 1 To 8 c.c. of Bottu's reagent 2 in a test-tube add i c.c. of the 

 urine under examination and mix the liquids by gentle shaking. Now heat the 

 upper portion of the mixture to boiling, add an additional i c.c. of urine and heat 

 the mixture again immediately. The appearance of a blue color accompanied by 

 the precipitation of small particles of indigo blue indicates the presence of glucose 

 in the urine under examination. The test will serve to detect the presence of o.i 

 per cent of glucose and is uninfluenced by creatinine or by ammonium salts. 



5. Reduction Tests. To their aldehyde or ketone structure many 

 sugars owe the property of readily reducing the alkaline solutions of the 

 oxides of metals like copper, bismuth, and mercury; they also possess 

 the property of reducing ammoniacal silver solutions with the separa- 

 tion of metallic silver. Upon this property of reduction the most widely 

 used tests for sugars are based. When whitish-blue cupric hydroxide in 

 suspension in an alkaline liquid is heated it is converted into insoluble 

 black cupric oxide, but if a reducing agent like certain sugars be present 

 the cupric hydroxide is reduced to insoluble yellow cuprous hydroxide, 

 which in turn on further heating may be converted into brownish-red or 

 red cuprous oxide. These changes are indicated as follows: 



OH 

 Cu ii Cu = O+H 2 0. 



\ Cupric oxide 



\ (black). 



OH 



Cupric hydroxide 

 (whitish-blue). 



OH 



Cu 



OH 



- 2Cu-OH-|-H 2 O-f O. 



OH Cupro ( ? s ell ^ rcxide 



Cu 



\ 

 OH 



1 Bottu: Compt. rend. soc. bioL, 66, p. 972. 



2 This reagent contains 3.5 grams of o-nitrophenylpropiolic acid and 5 c.c. of a freshly 

 prepared 10 per cent solution of sodium hydroxide per liter. 



